Fluid Power World Handbook June 2015

www.fluidpowerworld.com

June 2015

2015

Fluid Power

HANDBOOK

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Fluid Power

OVERVIEW

FP

HANDBOOK

WELCOME

2

to the fourth edition of the Fluid Power Handbook.

Once again this year, we’ve given the sections an updated feel, and I look forward to your feedback on these changes. You will find updated sections on many components and other areas of fluid power interest, along with several all-new topics, and a fascinating trends piece on the Internet of Things’ impact on fluid power technology.

This first year of Fluid Power World has been immensely successful, and I’m thrilled to see so many engineers return again and again for our unique, highvalue editorial content online. You can always visit www. fluidpowerworld.com for the latest and greatest news, application stories, technical features and more.

Fluid power is, quite simply, the use of a liquid or a gas to move a load and accomplish work. The technology is used in countless industrial as well as everyday environments, from automobile assembly lines to passenger airliners and from packaging equipment to huge earth-moving pieces of equipment.

Fluid power can be used for extremely tough tasks, such as boring new underground mining tunnels—or for very gentle operations, such as lifting and stacking large sheets of glass. Through various components and actuators, fluid power systems can push, pull, lift, rotate or grip almost any load.

While fluid power has been around for centuries, its heyday was undoubtedly sparked by the end of World War II, when countless soldiers returning to their home countries brought back their mechanical expertise and real-world experiences. The founding of many famed domestic fluid power component manufacturing companies—many still around today—can be traced to this era. In the years thereafter, some of the associations that have so shaped the industry were begun, most notably the National Fluid Power Association (1953) and the International Fluid Power Society (1960).

Fluid power systems are comprised of a myriad of components, including pumps, cylinders, valves, hose, fittings, gauges, sensors, filters, seals and reservoirs.

Some components are considered absolute necessities, while others are optional and used to refine the system for more precise operation or to increase the lifespan of the system or its individual parts. Throughout this handbook, we will detail many of the more

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common and widely used components, explaining their operation, their place in the system, and how an engineer should correctly specify them.

While fluid power can be used in most any industry or application, it is commonly seen in markets that include packaging, off-highway, mining, offshore/marine, medical, material handling, construction, aerospace, automation, robotics and entertainment.

And fluid power is an important technology. A 2012 study by the Department of Energy discovered that between 2.0% and 2.9% of the United States’ energy is transmitted through fluid power equipment.

While that is an impressive statistic, the study also found that the efficiency of fluid power averages 22%.

While that percentage is low, it also illustrates how much improvement there is to make. The study concludes that a 5% improvement in efficiency over 5 years is possible by instituting best practices in industry.

Or, even better, a 15% improvement over 15 years is possible with a strategic R&D program. Doing this would save the U.S. an amazing $37 billion.

While some say that fluid power is a static, mature technology, there’s still a lot in store for the technology.

As the Internet of Things continues to dominate the engineering news, we’re slowly seeing hydraulic and pneumatic components become more Internetfriendly, wireless and capable of being monitored and controlled from distant locations. We’re eagerly watching to see what the coming years will bring to the world of fluid power.

FPW

Pa u l J . H e n e y — Edi to ri al Di re cto r p h e n e y @ w t w h m e d i a . c o m — @DW_Edi t or

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02 Fluid Power Overview 06 SMART TECHNOLOGY 14 Gauges 18 Safety 24 Shock Absorbers and Linear Dampers

Smart

Technology

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26 Pneumatics Overview 27 Air Brakes 28 Air Compressors 32 Air Springs 34 Compact Cylinders - Actuators 36 Cylinders - Pneumatic Actuators 39 Cylinder Slides/Rodless Cylinders - Pneumatic 41 FRLs 44 Grippers - Pneumatic 47 Miniature Pneumatics 50 Vacuum Components 52 Valves - Pneumatic 57 Hydraulics Overview 58 Accumulators 61 Bar Stock 62 Clutches and Brakes 64 Cylinders - Hydraulic 71 Filters - Hydraulic 74 Filtration Systems 78 Fittings and Flanges - Hydraulic 86 Fluids - Hydraulic 88 Grippers - Hydraulic 90 Hose - Hydraulic 94 Hose Couplings - Hydraulic 99 Manifolds - Hydraulic 104 Motors - Hydraulic 108 Pressure Transducers 112 PTOs and Gearboxes 116 Pumps - Hydraulic 122 Replacement/Rebuilds 126 Rings 128 Rotary Actuators - Hydraulic 132 Seals 136 Valves - Hydraulic fluidpowerworld.com

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We don’t just sell the high end materials your company needs, we cut to order, so you are never stuck with wasted material again

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FLUID POWER WORLD does not pass judgment on subjects of controversy nor enter into disputes with or between any individuals or organizations.

FLUID POWER WORLD is also an independent forum for the expression of opinions relevant to industry issues. Letters to the editor and by-lined articles express the views of the author and not necessarily of the publisher or publication. Every effort is made to provide accurate information. However, the publisher assumes no responsibility for accuracy of submitted advertising and editorial information. Non-commissioned articles and news releases cannot be acknowledged. Unsolicited materials cannot be returned nor will this organization assume responsibility for their care.

FLUID POWER WORLD does not endorse any products, programs, or services of advertisers or editorial contributors. Copyright© 2015 by WTWH Media, LLC. No part of this publication may be reproduced in any form or by any means, electronic or mechanical, or by recording, or by any information storage or retrieval systems, without written permission from the publisher.

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The HyQ or Hydraulically actuated Quadruped robot helps humans during search and rescue operations. Moog developed the Highly Integrated Smart Actuator, which is integrated into the legs of the robot, to aid it in navigating rough and uneven terrain.

The custom-designed hydraulic actuator incorporates a sensor network, onboard loop closure for force, position and velocity control and EtherCat interface into one unit.

Smart Technology: It’s closer than you think Michelle DiFrangia • Assistant Editor

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WE ARE IN THE MIDST OF ANOTHER INDUSTRIAL

REVOLUTION, BUT THIS ONE

HAS US WITH OUR HEADS IN THE

CLOUDS AND OUR HANDS READY

TO CUT THE WIRES.

We

all know fluid power is a multifaceted technology, but it is also a mature one. Changes are coming, however, as companies look to tie fluid power components and systems into the Internet of Things, also referred to as Industry 4.0. In fluid power, the Internet of Things (IoT), refers to the concept of using data analytics on information coming from a multitude of sensors to increase productivity. Products can be embedded with wireless sensing technology that communicates to other devices or the operator through the Internet, or in some cases, the Ethernet.

While the IoT has only recently been receiving a lot of press, some companies have already recognized its importance and how it can affect the future of fluid power.

Gonzalo Rey, director of research and technology for Moog, identifies two categories of the IoT: device connectivity and the applications that exploit this connectivity. “Today, networking and device level connectivity and addressability are part of the typical fluid power installation landscape. The applications that exploit this fine grain connectivity themselves can be categorized as those that address device-level value added and those that aggregate this information to provide installation-level value,” he said.

“Moog products have connectivity; this is the extent to which we have implemented the IoT at this time,” he continued.

It seems the main focus for many companies implementing the IoT is on increasing uptime, productivity, efficiency and product quality. “By capturing data that exists within components and systems and making it available, we can create not only information, but actionable knowledge—from when a hose will fail to how a pump can be run more efficiently,” said Ben Hoxie, manager, Engineering Centers of Excellence, Eaton Hydraulics.

Beyond connectivity, Frank Langro, director of marketing and product management at Festo, said his company is “investigating technologies that support concepts such as de-centralized processes and customized manufacturing.” Bosch Rexroth is taking a similar approach. “We are combining hydraulics with digital controls and decentralized intelligence,” said Karl Tragl, president of the Executive Board. “We have developed a complete range of motion controls for hydraulics replacing valve functions by software.”

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SMART TECHNOLOGY

WHO

MAHKAETS W

EATON HYDRAULICS

PRODUCT: LifeSense Hydraulic Hose Condition Monitoring System

HANDBOOK

How it Works: The system consists of a hose diagnostic unit (HDU), sensor, hose and web portal. Wireless configuration that electronically monitors length of hose assemblies keeps track of data in real time and interprets the health of each assembly. The system will warn a user of impending hose failure immediately, giving time to repair or replace the hose before it fails.

FP

This brings up an important component of IoT, “Big Data” and cloud-based software, which allow the amount of data available to increase tenfold. But it’s not about how much data is gathered, rather what you do with it, said Jeremy King, product marketing manager, Bimba Manufacturing. “[We] take the knowledge of our products and combine it with ‘Big Data’ to provide real insights into how the actuator and system is performing.

These insights are the real value of Big Data.”

“As software services continue to grow and customers become more comfortable putting their business data on the cloud, they will start to see the value of moving manufacturing data there as well,” he continued.

Hoxie echoed King’s sentiments, adding that engineers are actively researching how future iterations of these products may be delivered through the cloud. “With data available in the cloud, information can be better tracked and used, giving customers needed information, as well as providing companies insight to how customers are using products,” he said.

But what about the risk factors associated with storing information on “the Cloud”? Alex Edwards, manager, Software, Electronics and Controls Center of Excellence at Eaton Hydraulics, offered

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this response: “There are real and perceived concerns over the security of products, which customers can mitigate by ensuring that safety measures are taken as integration occurs.”

Vast quantities of data can be overwhelming. Training is key to getting the most out of an IoT integration, said Edwards. “It is important to train staff to handle the increase of software and electronics on these products, and the data and analytics they provide.

This will allow customers to take true advantage of the opportunities the IoT offers.”

Successful integration Another key for successfully integrating IoT is adding it where it will be valuable without distracting from what is important, added Hoxie.

So where will IoT hold the most value? Are certain components better suited for integrating this technology? Some say yes, while others aren’t as ready to call out specifics.

“I think the natural progression is the use of sensor technology to facilitate the exchange and transmission of data,” said Langro.

Hoxie also points to components that are naturally more sensing oriented, such as control elements, as being more compatible.

However, he also said that components that have not historically seen controls, like hoses, can now be incorporated into the IoT and offer significant value.

Alternatively, King doesn’t think any one component of fluid power is more compatible than another. “It’s not the component that is important, but what that component does that matters,” he said, echoing his thoughts on Big Data. “If the component is critical to the customer’s operations, it should be connected to the IoT so new insights can be derived that help improve the user’s experience.”

Along the same wavelength, Rey said there is no barrier to incorporating the IoT. “As a device-level issue, they [components] are fluidpowerworld.com

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HANDBOOK

all more or less equally suited from a technology standpoint, provided electronics have bought their way into them already.

As far as ‘better suited,’ with respect to adding value to have a device as part of the IoT, it is hard to say because the IoT experience base is so limited at this time.”

Regardless of experience base, the advantages of integrating the IoT are numerous. Most notably is its ability to increase uptime and remote diagnostic capabilities. However, advantages vary based on who is looking at the data, said King. “From Bimba’s perspective as a component manufacturer, we now have our products telling us how they perform in a given situation … From the perspective of an OEM, IoT opens up many new business opportunities and allows them to differentiate on something besides prices. An MRO can increase uptime through predictive analytics,” he said.

Similarly, application also determines the types of data captured and its benefits to the end user. For example, said Edwards, the end goal in industrial equipment is typically automation, and so IoT becomes most important for simplifying configuration. “Knowing the energy consumption of an industrial machine can help customers make design changes to maximize efficiency,” he said.

On the other hand, in mobile applications, IoT is used to find component efficiencies and actionable items to maximize machine operator productivity. According to Hoxie, this is prevalent in large fleets of mobile equipment. “The data mining capabilities of the IoT are helping fleet managers remotely manage equipment and spot problems before they occur,” he said.

Perception versus reality With technology continuing to advance as rapidly as it has in the past decade, it’s easy to get caught up in the thrill of it all. When talking about the IoT in particular, this notion is exacerbated when the media is involved.

“The media is roughly 10 years too late to the topic,” said Rey, “and in a desire to ‘catch-up,’ it is generating a large volume of publications as it re-discovers the many facets of the IoT. This gives a sense of velocity that it is overblown.”

Tragl sees two possible misunderstandings about the IoT. First is that integrating the IoT is something only large corporations can afford. “Our experience at Bosch Rexroth is completely the opposite,” he said. “We follow an iterative approach where we decentrally realize many ideas on a small scale to gather experience. Step-by-step we expand successful

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pilot projects and introduce Industry 4.0 organically. I think this is also a good template for small- and medium-sized companies to start with.”

The second, but possibly most important misconception, is that plant floors will become fully automated and devoid of humans. This is not the case, said Tragl. “In the future, we will see a lot of people working together with machines. But their role will be different; they will more likely coordinate and control processes, which means that they will need different skills than today.”

This is not to say that the IoT will not affect fluid power in a big way. “Fluid power is typically a slowly changing market, so the changes the IoT makes may not feel sudden and dramatic, but rather steady and continuous,” said Hoxie. “It [the IoT] is a significant, longWHO

MAHKAETS W

BOSCH REXROTH

PRODUCT: Hydraulic Power Pack How it Works: Continuously monitors all relevant system states of the power unit. With its own intelligence, the HPU transforms this data into knowledge using condition monitoring and predictive maintenance functions to improve the uptime of machine efficiency.

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fluidpowerworld.com

ELECTRONICS VERSUS FLUID POWER: Some industry professionals might argue that electronics has an advantage over fluid power when it comes to implementing the IoT. What are your thoughts?

Jeremy King, Bimba Manufacturing It is as easy to get data from a fluid power device as it is from an electronic device. One has to simply integrate the sensors and connect them up. Providing data to the IoT is trivial; it is having people who understand what that data means that is important. In many ways, fluid power engineers have the advantage of knowing a lot more about the entire system so they can derive deeper insights from the data.

term trend, one which we may not fully understand the impact of until we are using the next generation of hydraulic products and components.”

“In 10 years, it will completely transform how people will interact with machines. A great place to see this is agriculture, whether it is smart tractors that help optimize planting and crop selection, or grain bin sensors to reduce spoilage,” added King.

Langro pointed out that some industry experts predict complete implementation of manufacturing facilities in 15 to 20 years, while others expect to see the transition sooner.

Regardless of timeframe, one thing is certain: Once the full economic value of the IoT is realized, implementation on some level will become almost mandatory.

“Any piece of equipment shipped from now on that is not able to upgrade itself to support the IoT technology evolution will be removed from service before the end of its design life and replaced by something that can support the up-to-date IoT standards and functionality,” said Rey. It looks like it’s safe to say that if you’re not actively researching the IoT, you should be, and your customers probably already are.

FPW

Ben Hoxie, Eaton Hydraulics We see electronics and fluid power as integrated solutions. Machines will continue to need the power and efficiency hydraulics provides, but with powerful intelligence electronics software provides. The future is in coupling these capabilities together for maximum configurability, efficiency, intelligence and power.

Frank Langro, Festo I tend to agree that the electronic-based products have a “leg-up,” so to say, in that they have an

WHO

MAHKAETS W

BIMBA MANUFACTURING PRODUCT: IntelliSense

How it Works: A remote monitoring platform for Bimba products, IntelliSense collects 2,002 data points per second from a single pneumatic actuator. Customers can then use the data to enhance uptime, product quality and machine efficiency.

inherent ability to transfer data that a purely pneumatic product might not have. However, the integration of pneumatics and electrics has evolved and will continue to evolve, making it feasible to integrate sensors and communications into traditionally “dumb” products like air supply units or cylinders.

Gonzalo Rey, Moog It is hard today to find a piece of a fluid power kit that does not have electronics. If … the question means “pure” electronics … then one element of their advantage is that their obsolescence horizon is much shorter than for a fluid power installation.

That makes it easier to keep the installed base up-to-date with the IoT, and therefore, a lot easier to support. To combat this, fluid power devices must support safe and convenient field upgrades.

fluidpowerworld.com

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CREDITS

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HANDBOOK

Special thanks to the following companies who helped supply editorial content and images for this edition.

R

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with custom scales are more common and digital pressure gauges with customizable firmware allow process measurement of pressure-based measurement of leaks or other parameters like torque, load, force and hardness.

Pneumatic and compressed air systems are also rife with gauges, as pressure is also measured in many locations throughout the system. Pressure is measured at the receiver(s), as well as at every FRL or stand-alone regulator in the system. Sometimes pressure is measured at pneumatic actuators as well. Typically, pneumatic pressure gauges are rated for not much more than 300 psi, although typical systems run around 100 psi.

Pressure is measured in three ways—absolute, gauge and vacuum.

Absolute pressure is a measure of actual pressure including ambient air, which is zero-referenced with a perfect vacuum, but can be as high as 14.7 psi at sea level. Absolute pressure readings are considered in applications interacting with ambient air, such as the compression ratio calculation for flow (cfm) requirements. Gauge pressure is zero-referenced against ambient pressure and is used in most applications operating in, but not with, ambient air, such as in fluid power systems. Disconnected from equipment, gauge pressure will read zero. Finally vacuum “pressure” is expressed in Torr, or referenced against ambient pressure,

pressure gauge is a fluid intensity measurement device. Pressure gauges are required for the set-up and tuning of fluid power machines, and are indispensable in troubleshooting them. Without pressure gauges, fluid power systems would be both unpredictable and unreliable. Gauges help to ensure there are no leaks or pressure changes that could affect the operating condition of the hydraulic system.

The hydraulic system is designed to work in a set pressure range so the gauge must be rated for that range. Hydraulic pressure gauges are available to measure up to 10,000 psi, although maximum hydraulic pressure is typically in the 3,000 to 5,000 psi range. Hydraulic gauges are often installed at or near the pump’s pressure port for indication of system pressure, but can be installed anywhere on the machine where pressure needs to be monitored—especially if sub-circuits operate at a pressure rate different from pump pressure, such as after a reducing valve. Often, pressure-reducing valves have a gauge port to tap into, allowing you to directly monitor its downstream pressure setting.

Pressure gauges have been used in fluid power systems for well over a hundred years, so it might be a surprise that pressure gauge designs continue to evolve. The evolution of pressure gauges for fluid power applications has, generally, been an increase in application specific features. For instance, pressure gauges are now more routinely designed with hydraulic friendly pressure connections (such as SAE/Metric straight threads) to prevent system leaks. Analog gauges

psi

as with “in.-Hg” (inches of mercury) units, which measures pressure below ambient.

The hydraulic gauge can withstand different pressure ranges based on what type of gauge style it is and what material it is made out of. Because of this, the gauge style and the material make up two of the most important selection criteria for gauges.

They are many types of gauge styles, the most common being Bourdon tubes and bellow gauges. Bourdon tubes function by taking the pressure and converting it into mechanical energy.

This energy moves a dial in the gauge, displaying the current amount of pressure in the system. Bourdon tube gauges are currently some of the most common gauges and have different configurations such as curved, helical and spiral. The different style of tubing, the size of fluidpowerworld.com

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the tube and the material it is made out of all vary based on the pressure range. One important characteristic to note is the cross section of the tubing changes with increasing pressure. Generally, as the working pressure of the gauge increases, the shape of the cross section of the tube’s design will gradually change from an oval shape to a circular shape.

Bourdon tube operation is simple. They consist of a semicircular and flat tube of metal, fixed at one end and attached to a sensitive lever mechanism at the other. As pressure increases inside the tube, the force of the fluid attempts to straighten out the curved tube. The tube then pulls away from the lever, which being connected to the needle on the display, shows the pressure at the fluid port.

While bellow gauges function similarly to Bourdon tubes, they differ in the fact that they use a spring to judge the amount of energy to push the dial. The spring is expanded and compressed by the pressure in the tubes and the energy created by that movement is transferred into gears that move the pressure dial.

The pressure range at which the gauge will be working is a primary selection factor for the type of material used to make the gauge. Gauges operating at higher pressures generally tend to be made of materials such as steel; when operating at lower pressures, they tend to be made of bronze.

Most pressure gauges in North America come with a 1⁄4-in. NPT male, but SAE thread is gaining popularity. The use of test-point adapters at various locations on the hydraulic system allows for measurement during troubleshooting without having to purchase dozens of pressure gauges. The test-point fitting attaches to the gauge, which can be screwed onto the test points throughout the circuit, allowing you to connect under pressure to measure at various points in the system. Most gauges are 21⁄2 in. in diameter, and can be either top-mount or panel-mount styles, but gauges are available in every size, material and construction imaginable.

Whether used for testing equipment or operating machinery, the right pressure gauge helps reduce costly downtime. In mechanical gauge applications for hydraulic systems, the common threats to gauge reliability are vibration, pulsation and pressure spikes.

Therefore, it’s best to look for gauges designed specifically for hydraulic applications. These features include: a forged brass case to prevent resonant frequencies from destroying internal components; a liquid-filled case to protect the gauge from vibration and extreme pressure cycles; and a restrictor to prevent damage to the gauge from pressure spikes. Although the liquid used in the gauge varies from application to application, glycerin is commonly used and performs well in many conditions. The higher the viscosity of the liquid, the more it dampens the vibrations. When choosing between a dry, wateror glycerin-filled gauge, it is also important to consider the following: temperature range, needle response time required, changes in pressure and the amount of vibration expected from the application.

Finally, depending on the demands of the application, gauge accessories, such as specialized restrictors, piston snubbers or even diaphragm seals, may be needed to prevent premature gauge failure.

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SAFETY SAFETY

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HANDBOOK

is a critical aspect to any fluid power system, not just from the basic level of keeping components plumbed properly, but also in overall levels of machine safeguarding. It is critical to evaluate the entire system, including the electrical portion, to minimize exposure to unnecessary risk. Systems are rated based on the weakest link in the control chain.

Several standards (including ISO 138491:2006, ANSI/ASSE Z244.1-2003 [R2008] and ANSI/ PMMI B155.1-2011) define the control system as including not only input, sensing and interlock devices, but also output devices such as pneumatic and hydraulic valves.

The function of a fluid control valve mimics that of an electrical-control relay and, therefore, is subject to the same rules for classifying safety integrity. Thus, properly specified machine safeguarding systems include provisions for pneumatic valves, including: • must be functionally redundant • must be monitored for faults (including diminished performance faults, which may create the loss of redundancy), without depending on external machine controls or safety circuitry • must return to a safe position in the event of a loss of pressure or other such event • must be able to inhibit further operation upon detection of a fault condition until such condition is corrected

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• should have a dedicated, specific functionreset input and should prohibit the ability to perform a reset by simply removing or reapplying pneumatic or hydraulic power, and • must not automatically reset.

Providing control reliability with fluid power is not quite the same as with electrical controls, however. For instance, plain redundancy in a safety circuit requires the equivalent function of four valve elements, not just two. Two of the four valve elements handle the inlet function while the other two elements handle the stop function (energy release). Many self-designed systems risk

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having hidden, potential flaws, which can lead to unsafe conditions because they are unseen, unexpected and, therefore, excluded from design and safety reviews. A good example is the spool cross-over conditions or ghost positions of a valve, which are usually not shown on schematics.

Two general abnormal conditions can affect valve safety. The first is similar to an electrical-control fault, such as when a relay might be stuck in the open or closed position. The second abnormal condition is when a valve develops diminished performance, as when it becomes sticky or sluggish.

In such cases, the valve reaches the proper position, but slower shifting affects safe stopping distances or precise timing. The ANSI B11.192010 standard mandates a monitoring system that detects these conditions for critical applications and the ANSI/ PMMI B155.1-2011 standard requires diminished performance monitoring if stopping time can be affected. An easy solution is to use a self-monitoring, Category-3 or -4 valve, designed to detect both conditions.

The use of double valves remained relatively unheard of for many years, except in a few select industries, such as stamping presses, which first initiated control reliability requirements.

Double valves provide dual internal functions (redundancy) so that an abnormal function of one side of the valve does not interfere with the overall normal operation. At the same time, the double valves sense abnormal operation on either side of the valve and then inhibit further operation until the problem has been corrected and the valve deliberately reset. This sensing and inhibiting function is commonly referred to as monitoring.

Two standard air valves, whether in parallel or in series, cannot perform the same safeguarding function as a fluidpowerworld.com

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HYDRAULIC SAFETY:

FP 

FLUID POWER SAFETY

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HANDBOOK

Safe hydraulics involves the consideration of a safe machine, first and foremost, and this is regardless of the form of motivation.

The two most critical considerations in hydraulic safety are with control of flow and pressure. Safe control of loads being manipulated by hydraulics is often primary. However, the safe containment of pressurized fluid often means loads are also stable, as a catastrophic leak of fluid could cause a failure of the system to control the load.

Safe control of a hydraulic load involves ensuring fluid is accurately metered. The potential for pressure and/or load-induced pressure to impart energy into oil is high. As such, the oil wants to give up that energy to the ambient surroundings, but is prevented from doing so by only the integrity of the components and conduits of the hydraulic system. The pressure either wants to escape past flow control or directional valves, or it attempts to exit to atmosphere through seals or plumbing failure points.

When fluid is well controlled through some sort of metering device, such as a flow control, counterbalance or proportional valve, the actuators and loads are prevented from running away. For example, when a cylinder is installed rod down, and loads are typically in tension, it is often installed with a meter-out configuration to prevent the load from running away with the cylinder. Although it is a safe method to prevent a runaway load, rodside pressure intensification can be a risk. If intensification blows out piston seals, then the load can drop regardless, which is counterproductive to the meter-out philosophy.

To avoid the pitfalls of metering out, a counterbalance valve can be used instead. The counterbalance valve is considered a pressure valve, but in reality, it controls the speed of an actuator. These valves ensure a cylinder will only

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HYDRAULIC SAFETY CONTINUED:

move as rapidly as pump flow is dictating, regardless

FP

HANDBOOK

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load-induced movement as the latter valve is.

of load-induced pressure or intensification. If a pilot

Pressure is the very essence of a hydraulic system,

signal is not seen from the opposite work port, the

and it is required to provide the force density that

valve remains shut, preventing the load from dropping.

makes a hydraulic system so effective. But pressure can

Often mounted directly to the cylinder work port, the

easily rise through intensification, load spikes, “water-

counterbalance valve also prevents dropping loads

hammer,” and thermal expansion, to name a few. If

when hose or tube failures occur.

pressure isn’t controlled and limited, components can

A leak in the cylinder hose or tube can also

fail, seals can give way and either example can render a

cause catastrophic failure and personal harm. When

machine unsafe. For this reason, hydraulics uses many

fluid is free to exit the actuator at a broken conduit,

types of pressure control valves.

it can no longer hold a load up. The counterbalance

Relief valves are used to limit pressure, preventing

valve prevents the load from dropping should there

damage and limiting power requirements. A relief

be a conduit failure. A pilot-operated check valve will

valve is often used to control main system pressure

provide the same safety function of a counterbalance

or isolated sub-circuits. Some circumstances require

valve, but is designed for static load-holding. It will hold

sub-circuits to operate at different pressures than

a load indefinitely, but is not as smooth at controlling

others, and the pressure-reducing valve can achieve

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this. It limits pressure downstream of itself, and in some cases, can be a reducing-relieving valve as well. This type of valve can control downstream pressure spikes or thermal expansion, where heated fluid increases in pressure. Some hydraulic systems can use a combination of various pressure valves to ensure circuit pressure is safely limited at every part of the machine.

So by controlling both pressure and flow in a hydraulic system, best practices of safety can be observed. A machine failure is unsafe in the best scenarios, so ensuring a hydraulic circuit is designed for safety will prevent injury to operators.

double valve providing this critical function.

By simply incorporating two standard air valves into the circuit, no provision is made to sense the abnormal operation of one side of the valve or, even more preferable, diminished performance such as slow shifting.

In addition, there is no provision for inhibiting further operation of the circuit until the valve is repaired. If one valve actuates abnormally, the second one continues to function and redundancy is lost. The circuit doesn’t recognize lost redundancy, nor would it halt operations as a warning that redundancy has been compromised. Then, if the second valve also actuates abnormally, there is no back up, and control integrity no longer exists.

Double valves are appropriate for pneumatic and hydraulic equipment anytime reliability is an issue. Typical applications include e-stop, two-hand-control, light curtains, safety gates, pneumatic locking devices for safety gates, hydraulic brakes, air brakes, amusement rides, hoists, elevators, pinch-point applications, or any other application where control system integrity depends on valve operation.

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Shock Absorbers &

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HANDBOOK

LINEAR DAMPERS

24

USE AND WHAT IT IS Shock Absorbers and dampers work to provide smooth deceleration of a given payload. A pneumatic or hydraulic shock absorber will use fluid or gas power for deceleration, and a spring to return the piston to its initial position. However, linear dampers typically do not. They facilitate the smooth closing of hinged doors, such as garage doors.

Important parameters for the proper selection of a linear damper can be broken up into general, dimensional, performance, material and features.

WHAT ARE THE SELECTION CRITERIA? The general criteria when selecting a shock absorber are the dampening method and damping direction.

The dampening method can be elastomeric, pneumatic or hydraulic. The damping direction can be either in compression or extension.

When choosing a shock absorber, one must specify the stroke length, compressed length, extended length, cylinder diameter, and rod diameter. The stroke length is the distance between the compressed and extended length. The cylinder diameter is an important factor in determining whether the cylinder will fit into the desired housing, or what housing to use. The rod diameter is used to determine how the shock absorber will be affixed to a given component.

The performance of the shock absorber can be determined from the maximum force, energy per cycle

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and maximum cycles per minute. The maximum force, also called the P1 force, is the greatest rated force that the shock absorber can supply. The energy per cycle is the amount of energy that the component can absorb, and will also depend on the stroke length.

The maximum cycles per minute is a measure of how quickly the shock absorber can return to its unstretched length.

Shock absorbers may be made from aluminum, steel and stainless steel, or thermoplastic. Steel is used when strength is required. The other materials provide varying balance between strength and corrosion resistance.

Additionally, the rods can be treated with chrome to provide corrosion resistance and increase surface hardness. Nitride will increase the hardness by introducing nitrogen into the outer surface of the rod.

There are also a number of important shock absorber features to consider. Adjustable shock absorbers allow the stiffness of the response to be monitored and fine-tuned. This is usually accomplished by adding or removing hydro/pneumatic medium from the shock absorber by way of a valve. Locking capability allows the position of the rod to be fixed at a given position.

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HANDBOOK

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Pneumatics

OVERVIEW PNEUMATICS

is the technology of compressed air, but in some circles today, manufacturers choose to refer to it as a type of automation control. Pressurized gas—generally air that may be either dry or lubricated—is used to actuate an end effector and accomplish work. End effectors can range from the traditional cylinder design to more application-specific devices such as grippers or air springs. Vacuum systems, also a part of the pneumatic realm, use vacuum generators and cups to handle delicate operations, such as lifting and moving large sheets of glass or delicate objects such as eggs.

Engineers commonly use pneumatics in industries such as medical, packaging, material handling, entertainment and even robotics. What’s more, pneumatics can be useful in applications where hazards are critical—for example, in a mine or on an offshore oil platform—where a single stray spark could mean total disaster and lost lives.

By its nature, air is easily compressible, and so pneumatic systems tend to absorb excessive shock, a feature that can be useful in some applications. Most pneumatic systems operate at a pressure of about 100 psi, a small fraction of the 3,000 psi

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that many hydraulic systems experience. As such, pneumatics is generally used when much smaller loads are involved.

A pneumatic system generally uses an air compressor to reduce the volume of the air, thereby increasing the pressure of the gas. The pressurized gas travels through pneumatic hoses and is controlled by valves on the way to the actuator. The air supply itself must be filtered and monitored constantly to keep the system operating efficiently and the various components working properly. This also helps to ensure long system life.

In recent years, the control available within pneumatic systems (thanks to advanced electronics and componentry) has increased a great deal. Where once pneumatic systems could not compete with many comparable electronic automation systems, the technology today is seeing a renaissance of sorts.

More and more, pneumatics is being used in interesting ways that would have been unthinkable a decade or two ago.

Creative applications from robotics to pneumatic muscles are consistently making the news, showing not only the creativity of the engineering community, but also the inherent flexibility and adaptability of this important technology.

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Air brakes

& CLUTCHES AIR

FP  HANDBOOK

brakes serve as the main brake to provide parking and E-stop braking functions in a variety of applications, including draglines, grinding mills and shovels in mining, drawworks for drilling rigs, and marine winches. They provide the quick actuation and stopping times that are necessary in emergency situations or to stop large industrial machines for routine maintenance. They are actuated with compressed air rather than hydraulic fluid or oil.

Air clutches help transfer torque between the engine and transmission, rather than providing stopping power. They rely on compressed air for engagement and disengagement. By controlling the air pressure applied to the clutch, you can achieve smooth controlled deceleration and even rapid stops. In addition, they offer quick and safe disengagement.

Air brakes are rotors or discs attached to a driveline shaft that, when the brake is applied, bring the rotating machinery to a stop. When the brake is applied, a piston is pneumatically actuated, forcing the friction pads to clamp the rotor discs. Several factors go into sizing an air brake; most notably, the required horsepower, stopping time and total energy are musts for selecting the right brake for the application.

Drum-style constricting clutches are pneumatically actuated and are used to connect and disconnect to rotating shafts to transmit power and motion.

Air-actuated brakes and clutches offer a number of advantages, such as fast response rates and safe operation. Since they are pneumatically actuated versus hydraulically actuated, the risk of spills, leaks and fires is eliminated. Leaked or spilled oil can create an incident that can take hours or days of downtime to clean up, creates a hazardous working environment and puts end users at risk of expensive environmental fines.

Unlike electrical options such as variable frequency drives and other AC drive motors, air brakes are capable of not only stopping motion, but also manual operation in the case of a power failure.

Electrical options are usually more complex as a result, and may require some type of a fail-safe brake to slow or stop motion in case of power outage.

To meet the needs of more complex machinery, newer brakes and clutches can include sensing and monitoring technology to make the equipment more responsive and able to provide feedback or warn users of problems. Solutions on the market today include brake and clutch products with embedded temperature sensors or slip detection.

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AIR COMPRESSORS

FP

HANDBOOK

AIR

compressors supply the compressed air flow for all pneumatic equipment in a system.

The compressor adds energy to the air, which is cleaned and conditioned by filters and dryers, then transmitted in piping for use by tools, equipment and processes. Compressed air is an energy intensive source of process power, about 7 to 8 units of energy are consumed at the compressor for each unit of mechanical energy produced by a typical compressed-air powered device—and of this, typically 50% of the compressed air is wasted due to leakage and inappropriate use.

Most of the energy released by an air compressor is in the form of heat of compression.

When discussing compressed air flows, there are various definitions that relate to compressor capacity: ACFM—actual cubic feet per minute (also called free air delivered, FAD, or inlet cubic feet per minute, ICFM).

This is the flow of air taken in by the compressor at site conditions (local atmospheric pressure, temperature and humidity). In general, higher altitudes, temperatures and levels of humidity reduce the capacity of the compressor to produce a given mass of compressed air; therefore, if these conditions exist, a larger compressor must be purchased.

CFM—cubic feet per minute. This is the flow of air at a certain point at a certain condition, which must be specified.

With regard to sizing air compressors, it is important to understand the wide range of conditions at which the CFM can be stated.

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SCFM—standard cubic feet per minute. This is the flow of free air measured and converted to a set of standard conditions. The definition of SCFM for air compressor rating purposes (Compressed Air and Gas Institute based on ISO Standard 1217) is the flow of air at 14.5 psig atmospheric pressure, at 68° F and 0% relative humidity.

It is important to note that ACFM and SCFM are both measured at atmospheric pressure, not at the pressure the air compressor produces.

There are two types of compressors: positive displacement and dynamic (also called centrifugal or axial).

Positive displacement air compressors Positive displacement compressors take in air and mechanically reduce the space occupied by the air to increase pressure. Dynamic compressors use the mechanical action of rotating impellers to transfer pressure to the air.

Positive displacement compressors can further be divided into rotary and reciprocating types. Rotary compressors are available in sizes from 5 to 600 hp. In rotary screw compressors, filtered air enters the inlet of the air end where male and female rotors unmesh. The air is trapped between the rotors and the air end housing. This space is reduced as the rotors remesh on the opposite side of the air end. Thus, the air is compressed and moved to the discharge port. For lubricated compressors, cooling fluid is injected into the housing, which mixes

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Air compressors run most efficiently at full output, but there is seldom a demand for full output on a continuous basis. For that reason, the output flow and pressure must be regulated, usually by one of several methods: On/off operation—motor on smaller compressors is started and stopped to maintain pressure Load/unload—inlet air valve is opened or closed to maintain pressure Modulation—inlet air valve is controlled proportionally by choking off the inlet flow to maintain output pressure Variable displacement control—displacement of the compression chamber is reduced to produce a lower flow and constant pressure Variable speed control—the speed of the compression element is varied to adjust the output flow and to maintain constant discharge pressure

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REDUCING ENERGY COSTS WITH BETTER CONTROL

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with the air to seal, lubricate and remove the heat generated by compression. This fluid forms a thin film between the rotors that virtually eliminates metal-to-metal contact and wear. The fluid is separated from the compressed air, cooled, filtered and returned to the injection point. The compressed air passes through an after-cooler and water separator to reduce its temperature and water content so it is ready for the air treatment equipment.

Because the cooling takes place right inside the compressor package, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air-cooled or water-cooled compressor package. Advantages of the rotary screw compressor include smooth, pulse-free air output in a compact size with high output volume over a long life.

Rotary screw air compressors are easy to maintain and operate. Capacity control for these compressors is accomplished using several methods with varying levels of efficiency; therefore, it is important to consider what type of control is to be used in a system (see sidebar).

In general, variable speed and variable displacement controls are the most efficient ways to run rotary screw compressors at partial loads.

Oil-free rotary screw air compressors use specially designed air ends to compress air without oil in the compression chamber, yielding true oil-free air. Oil-free compressors are typically two-stage units and are more costly than lubricated types. Oil-free rotary screw air compressors are available as air-cooled and water-cooled, with both load/unload and variable speed control options.

They also offer the same flexibility as oil-flooded rotaries when oil-free air is required.

Reciprocating air compressors use a piston within a cylinder as the compressing and displacing element.

Single-stage and two-stage reciprocating compressors are commercially available. Single-stage compressors are generally used for pressures in the range of 70 to 100 psig and two-stage compressors are generally used for higher pressures in the range of 100 to 250 psig. These types of units are most often used for smaller systems. Typically, these compressors are not rated for continuous duty due to limited cooling methods and should be operated at duty cycles of 60% of full capacity or lower, or equipment damage may result.

AIR COMPRESSORS

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Shortfalls of the start/stop and load/unload methods include higher mechanical wear and tear on motors and bearings. With load/unload, even during unloaded operation, the motor draws substantial power while performing no useful function. Modulation control is the least efficient way to control a compressor, with the power input dropping off only 3% for every 10% decrease in flow. Variable displacement control provides a better alternative for the upper 50% of capacity, but during low demand, power consumption can still be significant.

Often, an efficient alternative is to use variable speed control, where the power drops in almost direct proportion to the flow reduction.

This control is usually accomplished using a variable-frequency (speed) drive (VFD or VSD). Energy savings of 20 to 30% and higher compared to other methods of control are common when this control is used on systems with varying load. Other benefits include less wear and tear on compressor components, due to softer starts and elimination of cycling; lower peak demand for electric power; quieter operation; and improved power factor. VFD controls require good environmental conditions and good maintenance to ensure they are trouble free.

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AIR COMPRESSORS

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FP 

HANDBOOK

The reciprocating air compressor is single-acting when the compressing is accomplished using only one side of the piston. A compressor using both sides of the piston is considered double-acting.

Reciprocating air compressors are available either as air-cooled or watercooled in lubricated and non-lubricated configurations and provide a wide range of pressure and capacity selections.

Generally, special consideration needs to be given in sizing air dryers for these compressors due to possible high discharge temperatures.

Control of reciprocating compressors is normally through efficient start/stop control for smaller units of about 50 hp and below or load/ unload control for larger units. For larger, multi-stage compressors, each stage can usually be unloaded separately for efficient stepped control. Large multistage reciprocating compressors are now considered obsolete except for specialty purposes such as high-pressure or PET bottle blowing applications.

Dynamic air compressors The centrifugal air compressor is a dynamic compressor, which depends on transfer of energy from a rotating impeller to the air. Centrifugal compressors produce compressed air by converting angular momentum imparted by the rotating impeller (dynamic displacement). To do this efficiently, centrifugal compressors rotate at higher speeds than the other types of compressors.

Adjusting the flow by straight modulation or with the use of inlet guide vanes is the most common method to control capacity of a centrifugal compressor. By closing the guide vanes, volumetric flows and capacity are reduced with good turn-down efficiency. However, this adjustment is limited to the upper range of flow, with the use of inefficient blow-off required to ensure the compressor does not go into a damaging condition called surge.

Centrifugals can also operate using load/unload style control and have

minimal unloaded power consumption.

This can be a good energy efficiency measure. Efficient control of systems using multiple centrifugals requires coordination of the modulation controls and load/unload to ensure the compressors are kept from blowing off and that the compressors operate at their most efficient discharge pressure.

The centrifugal air compressor is an oil-free compressor by design.

The oil-lubricated running gear is separated from the air by shaft seals and atmospheric vents.

Dynamic compressors are most often used on sizeable compressed air systems. These units are most efficient where large continuous flows of compressed air are required. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants, and natural gas processing plants.

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When using variable speed control in a system with

REDUCING ENERGY COSTS WITH BETTER CONTROL, CONTINUED.

multiple compressors, the control of the system must be carefully coordinated to ensure the VSD compressor always runs at the trim compressor (unit taking partial load), rather than at full load where a VFD-controlled compressor often consumes more power than fixed-speed compressors. A properly coordinated system should run all the standard fixed-speed compressors fully loaded or turn them off. Compressors outfitted with automatic controls can turn themselves off to save power when not required and remain armed for start when they are needed.

Retrofit of a standard fixed-speed compressor to a VSD should be done with the utmost care and is not generally recommended because different motors and compressor screw elements are needed for efficient and trouble-free variable speed duty. It is best to purchase a pre-designed unit that is actually optimized for VSD operation. These are available from most compressor manufacturers.

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TYPICAL PACKAGED VFD used on compressors from 150 to 500 hp.

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Every day at Minnesota Rubber and Plastics we produce high performance components and assemblies for the most demanding applications.

Our experience in advanced material formulation enables us to meet increasingly stringent regulations and your unique product requirements. Our over 60 year history in the design and manufacture of Custom Molded Rubber, Plastics and Assemblies

complex devices makes us the preferred partner for industry leaders throughout the world. The next time your component or assembly project seems impossible, there’s no one better to partner with than Minnesota Rubber and Plastics. We’ll make your tough application a reality.

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FP

HANDBOOK

AIR SPRINGS

32

AIR

springs have been used in heavy-duty vehicle suspension systems for nearly a century, where they have been able to provide usefulness by taking advantage of the compressed air required for vehicle braking systems. Air springs have provided a two-fold advantage over mechanical leaf or coil springs. One advantage with air suspension is the extra comfort provided by being able to vary the air pressure inside the spring, which changes the spring rate, and therefore, ride quality.

Additionally, because variable control over air pressure adjusts the deck or trailer height, aligning loading docks to the level of the deck is possible when dock plates are unavailable.

The usefulness of air springs or actuators didn’t go unnoticed in the industrial machine industry, and it was clear they could offer unique solutions for various applications. Air actuators have seen duty as shock absorbers, linear actuators, vibration isolators and tensioners, to name a few examples. They can be used to absorb shock in FLUID POWER WORLD

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material handling applications, such as a saw mill, when logs are dropped onto processing stations. Air springs make some of the best vibration isolators on the market, such as would be used on a vibrating hopper or commercial laundry machine. In summation, air springs are a high-force, low-cost actuator that can operate in a linear fashion or at an angle. They can be stacked to provide longer strokes or greater angular rotation.

As air is directed into air springs, the bladders allow them to expand in a linear fashion. This permits them to be used as force developing actuators—like pneumatic cylinders—and as such, rod attachments are available to mimic the function of them. Most often, however, an air actuator is simply two end plates connected by a bladder, and as they are pressurized, force pushes the plates away from each other. As linear actuators, they can provide up to 35 tons of force, making them useful in various press applications, such as a forming press or small stamping press. Air actuators are also excellent for constant force applications, such as pulley tensioners or drum roller compression devices. All air springs are single-acting, unless they are coupled together so one extends while the other retracts.

The two major types of air springs are the rolling lobe (sometimes called reversible sleeve) and the convoluted bellow.

The rolling lobe air spring uses a single rubber bladder, which folds inward and rolls outward, depending on how far and in which direction it is moved. The rolling lobe air spring is available with high usable stroke length—but it is limited in strength because of its tendency to bulge, and therefore has limited force capacity. The convoluted bellow type air spring uses one to three shorter bellows, with the multiple units being reinforced by a girdle hoop. Convoluted air springs are capable of ten times the force of a rolling lobe version and twice the lifecycle rating, but have less usable stroke to work with.

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ContiTech Industrial Air Springs Offers Dual Functionality ContiTech’s industrial and off-highway air springs and air actuators offer dual functionality with many advantages over typical cylinders or vibration control components. With a broad product range and customized applications, ContiTech air springs master difficult vibration isolation and suspension applications in automated machinery, off-highway vehicles and plant engineering. Air actuators provide linear and angular force output from 112 lbs. to 44.5 tons of lifting power, with diameters from 2.4 in. to 37.4 in. and strokes of up to 22.8 in., with three different elastomeric bellows and base plate materials.

ContiTech North America To learn more visit www.contitech.us or call us at 1-800-654-0974.

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Compact

CYLINDERS COMPACT

SELECTING A COMPACT CYLINDER

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HANDBOOK

cylinders have been shortened relative to standard pneumatic cylinders. They may be up to 50% shorter than the normal cylinder, but still maintain the capacity to exert the same force as their larger counterparts.

Important parameters for the proper selection of a compact cylinder can be broken up into general, dimensional, performance, material and features.

The “Pancake cylinder” was the original compact pneumatic cylinder, invented by Al Schmidt in 1958, to fill a need for force in a tight, enclosed space. The basic intent was to get the most stroke in a short overall length using common machined parts and seals. Through the years, this design has been further developed, with many features and options to satisfy a variety of customer applications. This round body cylinder has a smooth, clean outside diameter for ease of machinery cleaning. Even though initially used for strokes less than 1 in., manufacturing methods have allowed increased strokes to as much as 4 in. Non-metallic rod bushings and piston bearings can accommodate extreme or unforeseen loads to provide long-term durability.

Other compact cylinders vary quite a bit. They can be square shaped, offer numerous mounting features and can be placed with adjacent cylinders at a close center-to-center dimension. Piston

Application data needed for sizing a compact cylinder and choosing the best component:

Other items to consider:

• Operating psi, force required

• Environment

(Force = Pressure x Piston Area) • Stroke

• Ambient temperature • Media temperature • Excessive loads other than required axial force

• Preferred mounting, foot print

• Load guiding (non-rotating)

• Spring return or double acting

requirement

bearings, materials, hard anodized bore and chrome plated rods can enhance cylinder capability for unexpected side loads and long-term durability. Up to 6-in. strokes can be accomplished with extruded body material. Other features may include metric dimensions, extruded sensor mounting and non-rotating styles.

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Pneumatic Actuators —

CYLINDERS MANY

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HANDBOOK

industrial applications require linear motion during their operating sequence. One of the simplest and most cost effective ways to accomplish this is with a pneumatic actuator, often referred to as an air cylinder. An actuator is a device that translates a source of static power into a useful output motion. It can also be used to apply a force. Actuators are typically mechanical devices that take energy and convert it into some kind of motion. That motion can be in any form, such as blocking, clamping or ejecting, but typical motions are rotational or linear in scope.

Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Unlike their hydraulic alternatives, the operating fluid in a pneumatic actuator is simply air, so leakage doesn’t drip and contaminate surrounding areas.

There are many styles of pneumatic actuators including diaphragm cylinders, rodless cylinders, telescoping cylinders and through-rod cylinders.

The most popular style of pneumatic actuator consists of a piston and rod moving inside a closed cylinder. This actuator style can be sub-divided into two types based on the operating principle: single-acting and double-acting.

Single-acting cylinders use one air port to allow compressed air to enter the cylinder to move the piston to the desired position, as well as an internal spring to return the piston to the “home” position when the air pressure is removed.

Double-acting cylinders have an air port at each end and move the piston forward and back by alternating the port that receives the high pressure air (Figure 1).

FIGURE 1 shows the primary components that make up a typical double-acting pneumatic actuator.

• In a typical application, the actuator body is connected to a support frame, and the end of the rod is connected to a machine element that is to be moved. A directional control valve is used to provide a path of compressed air to the extend port while allowing the exhaust air to escape through the valve to the atmosphere. The difference in pressure on the two sides of the piston results in a force equal to the pressure differential multiplied by the surface area of the piston.

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PNEUMATIC ACTUATORS — CYLINDERS

HANDBOOK FP

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• If the load connected to the rod is less than the resultant force, the piston and rod will extend and move the machine element.

Reversing the directional control valve will provide compressed air to the retract port, allowing exhaust to escape the extend port, and the cylinder will return back to its home position.

PNEUMATIC CYLINDER SELECTION: When selecting an air cylinder, it is important to properly match the cylinder to the application, particularly in terms of required force. The theoretical force available in the actuator is the piston surface area multiplied by the supplied air pressure.

Spring force must be subtracted from this value for singleacting cylinders. The actual force applied to the load will be 3

• Pneumatic actuators are at the working end of a fluid power system. Upstream of these units, which produce the visible work of moving a load, are compressors, filters, pressure regulators, lubricators, on-off control valves and flow controls (Figure 2). Connecting all of these components together is a network of piping or tubing (either rigid or flexible) and fittings.

Pressure and flow requirements of the actuators in a system must be taken into account when selecting these upstream system components to ensure desired performance.

Undersized upstream components can cause a pneumatic actuator to perform poorly, or even make it unable to move its load at all.

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to 20% less due to pressure losses in the system.

When the required piston surface area (A) is known, the bore diameter (d) can be found by the formula:

d=

4A π

Stroke length is determined by the required travel of the machine element driven by the actuator. The final selection criterion is the cylinder mounting arrangement and the resulting configuration.

There are many different configurations available from various manufacturers. The more common ones include rigid nose or tail mount, trunnion mount, rear pivot mount and foot mount. Once the basic actuator size and configuration are known, other options such as end-of-stroke cushions or special seals should be considered. In some applications, position detection switches are required, typically accomplished with a magnetic piston and switches.

There are many factors such as system contamination, corrosion, minor leaks and wear that will affect the available air pressure and flow used to drive the actuator. An actuator and fluid power system should be sized correctly so as not to waste

FIGURE 2 shows a basic pneumatic system to power and control a pneumatic actuator.

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energy, with a margin added to account for minor reductions in pressure and flow due to the factors listed above.

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Pneumatic cylinder slides/

RODLESS CYLINDERS PNEUMATIC

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SPECIFYING CYLINDER SLIDES:

HANDBOOK

FP

cylinder slides, and rodless cylinders (sometimes referred to as guided cylinders) are designed to provide power and linear motion while supporting a load. Stand-alone pneumatic cylinders are suitable for providing power and motion, but are not designed to provide support for a side load. Most of these types of cylinders have no way of holding the position of the piston rod, due to the rod’s ability to rotate. Pneumatic slides provide the load capability and a stable, non-rotating platform on which to mount tooling or other actuators. This is especially important when a cylinder is moving in a horizontal direction, or where side load is a major issue— common in automation devices used for picking and placing of parts.

Rodless cylinder slides are popular choices when longer distances of travel are required, or when the overall length must be minimized due to space constraints.

Typical uses for these slides include conveyor stops; part ejection and positioning; opening and closing safety doors, gates or curtains; and multi-axis configurations. In many of these applications, the need for side load capacity and non-rotating capability is critical.

The idea of applying a load to a linear actuator is common, and there are a number of types of cylinder slides that can be used for these applications. The first basic style of powered slide is commonly known as a “thruster” or cantilever type unit. This type of guided slide is typically powered by a rod-style pneumatic cylinder, which is attached to the body of the slide, or may be integral to the slide. In either case, the cylinder piston rod is attached to a tool plate providing power and motion. The tool plate is supported by a bearing mechanism, and together they are able to carry any loads that are attached, rather than transferring the load to the cylinder rod. This type of slide is designed to carry an overhung load known as a cantilevered load.

There are several considerations when selecting the best type of pneumatic cylinder slides. These include: • Load capacity required. The total payload must be calculated in order to start the selection process.

• Life required from the slide. The bearing system selected will have an impact on the expected life of the unit along with the required speed and payload.

• Speed required. The slide speed is a critical component including the ability of the slide to handle the kinetic energy as the load stops at the end of travel. Cylinder shock pads, cylinder cushions or shock absorbers may be required based on the load and speed of the slide.

• Deflection needed. The amount of deflection will vary based on the bearing system and the payload being carried. This deflection will affect the positional accuracy of the slide.

Many manufacturers of pneumatic cylinder slides provide specification and sizing software to allow the proper selection of the slide required for various applications.

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PNEUMATIC CYLINDER SLIDES/ RODLESS CYLINDERS

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The second basic type of cylinder slide is called a saddle slide or base slide. In this case, the pneumatic cylinder is attached to a saddle that supports the bearing system on each end of the slide’s travel. This type of powered slide can be used for longer travels with less deflection based on the bearing system being supported on each end. Like the thruster style slide, the saddle carries the load versus the cylinder’s piston rod.

Another type of slide is a rodless slide. In this case, the bearing system is attached to the rodless cylinder directly on one or both sides of the cylinder. The cylinder’s piston is linked to a carriage mounted upon the bearing system, offering load carrying capability as well as resistance to side loads. Rodless slides offer the most space savings as the cylinder’s travel is contained within its own overall length.

The types of bearing systems can vary on thruster slides, saddle slides and rodless slides. The most common type of bearing system on cylinder slides uses round shafts with linear bearings. The bearings can be precision reciprocating ball bushings or a variety of composite bushings. The precision ball bushings provide low friction and more than 200 mil in. of travel life. Composite bushings are typically lower in cost and can be used in harsh environments.

These have more friction and do not have the life expectancy of the reciprocating ball bushings. Rodless slides use either profiled rail bearing systems or reciprocating ball bearings, and in some cases, composite bushings. As with thruster or saddle slides, load and life is commensurate with the bearing system.

Other pneumatic cylinder slides use profile rails with reciprocating ball carriage bearings. The profile rail bearing systems provide long life with minimum deflection.

These can be incorporated in both thruster and saddle type slides.

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FRLs AIR

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FLUID POWER WORLD

HANDBOOK

Filters remove impurities from the pneumatic system, preventing damage to equipment and reducing production losses due to contaminant-related downtime.

Downtime in an industrial plant is expensive and is often the result of a contaminated and poorly maintained compressed air system.

The size of an air filter is selected based on the maximum airflow through the unit, and care should be taken in referencing the manufacturer’s flow characteristics chart. Just like any pneumatic component inlet and outlet pressure factor into air flow, but you should also consider the pressure drop characteristics of the filter itself, which can be high if the unit is undersized, causing a reduction in flow.

There are three types of filters: general purpose, coalescing and vapor removal.

General purpose filters are used to remove water and particles, coalescing to remove oil, and vapor removal to evacuate oil vapor and odor.

Pressure regulators reduce and control fluid pressure in compressed air systems. Regulators are also frequently referred to as PRVs (pressure reducing valves). Optimally, a regulator maintains a constant output pressure regardless of variations in the input pressure and downstream flow requirements, so long as upstream pressure doesn’t drop below that of downstream. In practice, output pressure is influenced to some degree by variations in primary pressure and flow.

Pressure regulators are used to control pressure to air tools, impact wrenches, blow guns, air gauging equipment, air cylinders, air bearings, air motors, spraying devices, fluidic systems, air logic valves, aerosol lubrication systems and most other fluid power applications requiring subordinated pressure.

Regulators employ a control-spring acting upon a diaphragm to regulate pressure, and its spring rate determines the range of pressure adjustment. General purpose regulators are available in relieving or non-relieving types. Relieving

FP

leaving a compressor is hot, dirty and wet, which can be damaging to—and also shorten the lives of—downstream components, such as valves and cylinders. Before air can be reliably used, it needs to be filtered, regulated and sometimes lubricated.

An air line filter traps particle and liquid contamination in compressed air. It strains the air to trap solid particles (dust, dirt, rust), and also separates liquids (like water and oil) entrained in the compressed air. Filters are installed in the line upstream of regulators, lubricators, directional control valves and air-driven devices such as cylinders and motors.

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HANDBOOK

FRLs

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regulators can be adjusted over a wide pressure range, and even when downstream flow is blocked at the reducing valve, relieving regulators will allow the excess downstream load- or head-induced pressure to be exhausted. Non-relieving regulators, when similarly adjusted, will not allow the downstream pressure to escape. The trapped air will need to be released by some other means, for example, by operating a downstream valve.

Downstream equipment flow and pressure requirements must be determined to properly size the correct regulator for the application. Similar to filters, manufacturers offer flow characteristic charts for their products to help chose the correct regulator.

A lubricator adds controlled quantities of oil or other lubricant into a compressed air system to reduce the friction of moving components.

Most air tools, cylinders, valves, air motors and other air driven equipment require lubrication to extend their useful life. The use of an air line lubricator solves the problems of too much or too little lubrication that arise with conventional lubrication methods, such as either grease gun or direct oil application. Once the lubricator is adjusted, an accurately metered quantity of atomized lubricant is supplied to the air operated equipment, and the only maintenance required is a periodic refill of the lubricator reservoir. Adding

SELECTING FRLs: The selection of an FRL assembly is based mostly on the flow rate required, and the size of the component bodies reflects this. Other than the required flow rate, construction material and component options are also considered.

Often in pneumatic systems, components are sized to match the connection ports on other components. For example, if your valve manifold inlet port is ¾-in. NPT, then choosing ¾-in. ports for your FRL might seem like the easy choice.

However, not all filters, regulators and lubricators are created equally, and selection of the FRL should be based on the flow characteristics of the assembly, rather than port size alone.

By referring to the flow charts provided by the FRL manufacturer, you can size the assembly to match the flow required. An important consideration of selecting FRL size is the flow characteristics of the regulator. Because the regulator limits and controls downstream pressure, the outlet pressure plays a critical role in the dynamic flow capability of the whole FRL assembly. If outlet pressure rises or is regulated too close to inlet pressure, the FRL will start to reduce flow, or even stop flowing altogether, as shown in Chart 2.

On top of flow limitations possible with the regulator, the flow of the filter and lubricator is calculated in Charts 1 and 3. Flow reductions are cumulative, as every inline component can reduce flow further, which emphasizes the importance of avoiding arbitrary FRL selection based on port size alone.

Construction material of the FRL components also plays a role in selection, and some of the metals and plastics in their construction might not be compatible with the ambient air conditions of their installation location. For example, the standard polycarbonate bowl construction of most filters are not appropriate for exposure to aromatic chemicals, and nylon should be used instead.

Finally, FRLs are available with many options, such as pressure gauges, drains, pressure switches and check valves, to name a few. If you’re unsure what you need, contacting the

CHART 1: This chart shows the typical flow characteristics for a filter unit. By first selecting the inlet pressure curve and then deciding upon an acceptable maximum pressure drop, the chart displays flow potential in scfm.

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manufacturer will put you in touch with someone to help with your decisions.

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FRLs

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FP HANDBOOK

lubrication to a system also “washes away” compressor oils that travel through the system in vapor form.

Mineral oils added to the system prevent synthetic compressor oil build-up on system components. When lubricators are not used in a system, a coalescing filter should be installed to remove compressor oil aerosols.

Lubricators are sized by downstream flow requirements, and an analysis of air flow use must be made to accurately determine lubrication rate. After determining how much air flow is needed, a lubricator can be chosen, and once again, manufacturers’ curves will be similar to the one shown.

FPW

Camozzi Solutions Air-Treatment FRLs

CHART 2: Typical performance characteristics.

Reliability and high performance

MODULAR FRL UNITS COMPACT, LIGHTWEIGHT RAPID ASSEMBLY PATENTED BOWL LOCKING MECHANISM INTEGRATED SOFT-START, SHUTOFF AND TAMPER-PROOF DESIGN

CHART 3: This charts the typical flow characteristics of an FRL lubricator. Once again, flow is calculated first by selecting the inlet pressure curve, deciding upon an acceptable maximum pressure drop, and then following the line down to show max scfm.

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Pneumatic

GRIPPERS PNEUMATICALLY

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HANDBOOK

operated industrial grippers have been commercially available for only a few decades, and prior to that, most gripping mechanisms were designed and fabricated by machine builders employing a combination of pneumatic cylinders and external tooling for each individual application. Their most common purpose is to grasp or enclose parts for transfer, insertion or assembly in automated manufacturing and processing systems. Additional uses may include operating in environments that are hazardous for human presence.

Pneumatic grippers provide their motion and actuation by introducing compressed air into a chamber of the device and powering a piston or a rolling diaphragm attached to a rod. The resultant motion of that rod is then converted mechanically to some form of gripping force. Grippers are typically available in either an angular or parallel jaw version.

The term parallel implies that the gripping surfaces of the jaws remain parallel to one another throughout the gripper’s travel, whereas angular refers to the pivoting motion of the jaws closing on the workpiece, such as would occur if you held your hands out to the side and then clapped out in front of you.

The simplest of the angular design is a basic linkage or toggle mechanism attached to a piston rod, which is then connected to one of the gripper’s jaws. A directly opposing linkage is attached to another jaw. These two opposing jaws then make up the simple angular gripping device. With the appropriately designed and attached tooling, this type of gripper can provide a fairly large force in an angular fashion. The force is generally directly proportional to both the pressure applied to the piston and the length of the linkage or toggle. The length of the tooling attached to the gripper also affects the force capacity, as the gripping point must be within the specified gripping distance/range.

One of the limitations of this angular style of gripper jaw motion is that lacking sophisticated tooling, it can only efficiently grip a limited size range of parts. A variation of this angular gripper could include a third, or even a fourth jaw, defining a center gripping axis or region.

The parallel gripper design employs one of several different types of mechanisms that convert the piston or its rod motion to a parallel jaw travel, including: • a lateral direct coupling of a pair of pistons to guided opposing jaws moving opposite each other, such as with a wide opening gripper • a design where opposing jaws are driven by a component of the

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PNEUMATIC GRIPPERS

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HANDBOOK

piston rod riding on a cam surface portion of the jaws • a rack, powered by pistons, driving a pinion that in turn employs a scotch yoke cam device to drive opposing jaws • a rather complicated mechanism where the piston or one of its members drives a scroll mechanism similar to a machine lathe-chucking device

SIZING GRIPPERS:

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All of these parallel mechanisms may also be designed to incorporate three or more jaws for gripping round or unusual shaped parts. Similar to angular grippers, typical parallel gripper forces are proportional to the applied pressure. Due to inherent friction within their jaw mechanisms, parallel grippers may also require de-rating factors based on the length of tooling attached to the jaws. While the parallel gripper may cost slightly more than a comparable angular version, it is considered by some to be advantageous over the angular

46

style because it can often be applied to grip a wider range of part sizes without changing the attached tooling.

Additional features of both angular and parallel pneumatic grippers include the ability to operate as dual-acting cylinders. This allows them to be used for gripping on either external or internal features of the part. The grippers may also be available with an internal spring, which can offer multiple functions: to use the gripper as a single-acting version with spring return; to prevent the dropping of the workpiece if air pressure is lost; or to provide supplementary gripping force in addition to the pneumatic force.

Material construction of most commercially available pneumatic grippers is aluminum with various surface treatments where additional abrasion characteristics are required.

Other materials could include stainless steel or even engineered plastics where corrosion resistance and washdown service is desired.

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Pneumatic grippers are available in a wide range of sizes developing grip forces from just

When sizing a gripper, you must factor

a few ounces to several hundred pounds. Gripper force development does not always

the mass of the object, the friction of

translate directly into the capacity to carry a specific load. Additional consideration must

the gripper material and the force of the

also be given to the actuator’s ability to withstand moments that are reflected back into

gripper itself. As a rule of thumb, the force

the jaws of the gripper from forces developed while in motion. Most manufacturers of

of the gripper should be 10 to 20 times

today’s grippers provide sizing assistance through their technical sizing manuals, sizing

the mass of the workpiece, depending

software or both.

on the coefficient of friction between the

Selecting a gripper requires you to first have an understanding of the object shape

attachments and that workpiece. If the

and path of pick and placement. If the shape and size of the workpiece are consistent,

coefficient of friction (µ) is 0.2 or higher, a

angular grippers will be acceptable for most applications. If the workpieces vary in size or

multiplier of 10 will suffice. If the coefficient

shape somewhat, parallel grippers will be required, as they have a wider range of usable

is 0.1 or lower, a multiplier of 20 will be

finger width. Some objects, such as a pill bottle, are best suited for three- or four-finger

required to ensure the gripper can safely

grippers, which can center the object as it is grasped.

handle the workpiece in most conditions.

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Miniature

PNEUMATICS IN

HANDBOOK

SE

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many ways, small is still the new big in pneumatics as of late. Whether it’s for end-use application purposes or to reduce manufacturing costs and increase efficiency—the trend to go small or go home continues.

Miniature pneumatics, sometimes called precision pneumatics, consists of a range of pneumatic components that have been miniaturized for use in light- and mediumduty applications with low-to-medium pressure ranges. Size and weight constraints matter in these systems and the need for precision is high. System pressures of 20 psi are not uncommon in miniature pneumatic applications.

Miniature pneumatics has found applications in medical/ dental instruments, test equipment, analytics, pharmaceuticals, entertainment/animatronics, semiconductor, HVAC systems, aerospace, down-hole oil tools, machine tools, ink-jet printing and process control systems.

Miniature pneumatic products encompass a range of scaled down parts, including valves, cylinders, fittings, manifolds and tubing.

Specialized components, such as nozzles and screens, are also seen on occasion.

For example, the evolution of medical equipment has expanded

FUL

S

PN

I

C

U

TERMS E U M AT

A selection of miniature fluid power

Plugs are the most successful method to seal

Flow controls including restrictor check

components currently available

drilled holes for critical applications. More

valves, directional flow controls and constant

include the following.

than 100 million are in use where permanent

flow valves are available in a wide range of

leak-proof seals are required.

sizes to suit many applications.

Restrictors offer small size, precision

Nozzles can produce either a hollow cone of

performance and long life. Single orifice and

atomized spray or an accurately targeted jet of

multi-orifice models cover a wide range of

lubrication fluid.

restriction and can be customized to meet special requirements.

Relief valves provide safety relief, linear or high pressure operation. They cover a wide range of applications.

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MINIATURE PNEUMATICS

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beyond the hospital environment and toward the home care and ambulatory environments. This has made portable battery operated variants of traditional stationary equipment more attractive. In today’s culture, the persistent demand for reliable and innovative products compels companies to integrate new and more advanced technology into smaller packages. The medical market is the major sector for growth in miniature pneumatics right now. Industry experts expect that in the near future, this will remain the case, especially for small solenoids.

A magnetically latched solenoid valve is suitable for reducing power consumption in applications where conventional, higher power valves have been used in the past. This type of design can be used for compact, batterypowered pneumatic instruments such as portable oxygen delivery systems, environmental gas samplers and other OEM flow switching devices.

Similarly, properly designed miniature solenoid valves can improve patient comfort by reducing actuation noise. A typical solenoid valve has an inherent clicking sound when energized, which is caused by the metal-to-metal contact of the moving armature and stationary core. Quieter operational design found in some miniature pneumatics uses so-called whisper technology to greatly reduce sound levels. These valves are used for medical applications flowing gas or air, such as dialysis machines, patient monitors, ventilators/respirators and other bedside medical devices.

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Shuttle valve styles include: spring biased with the

Piloting solenoid valves are designed for use

emergency port normally closed; detented, where

in aerospace hydraulic and fuel systems, oil tool

the poppet latches to close off either the emergency

applications and other challenging high-pressure

port or the normal port; selective shuttle valves with

applications. These are critical in space and weight

a non-biased loose ball design; and inverse shuttle

savings, as well as power consumption.

valves, where the lower pressure inlet port is open to common instead of the higher pressure inlet port.

Pressure components include miniature restrictors for damping pressure transients, adjustable

Safety screens protect hydraulic components from

pulsation dampers and miniature passive peak

contamination. Manufacturers offer intermediate-

pressure recorders.

and high-pressure etched screens; they can be customized to meet special requirements.

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www .theleeco.com

Go ahead, push us to your limits.

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If you need a fluid handling component for whatever reason, no matter how extreme, talk to The Lee Company. We’ve been solving complex fluid control problems in all kinds of industries for more than 60 years.

Our extensive family of precision fluid control products offers unsurpassed reliability in just about every configuration you could imagine, including:

• Miniature Solenoid Valves

We’re not just talking about off-the-shelf solutions, either. A Lee engineer will be happy to discuss your application, and develop a custom design if needed. From managing nanoliter droplets to creating fully integrated fluidic systems, we’re unsurpassed in breadth and experience to deliver the precise, reliable performance you require.

Whatever problem you face, make the solution easy.

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Vacuum

COMPONENTS the simplest sense, vacuum is pressure that is lower than atmospheric. At sea level, atmospheric pressure is usually 14.7 psia. Therefore, any pressure lower than that constitutes a vacuum. In a vacuum system, the difference between atmospheric and vacuum pressure creates the ability to lift, hold, move and generally perform work.

The essence of vacuum generation is the reduction of molecular impacts within a system. In effect, vacuum is the pressure differential produced by evacuating air molecules from a system.

There are two types of vacuum applications: sealed, or non-porous, and open, or porous. In a closed system, removing air progressively decreases the air density within the confined space. This causes the absolute pressure of the remaining gas to drop, causing a vacuum.

To achieve a vacuum in an open system, a vacuum unit must have the capacity to remove more atmosphere or air molecules than are able to leak back into the system.

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The following are the most important terms to be considered and understood in any discussion or application using vacuum.

VACUUM That pressure or any pressure lower than atmospheric. As previously discussed, at sea level atmospheric pressure is usually 14.7 psia; any pressure lower than that constitutes a vacuum.

VACUUM FLOW The rate at which atmospheric pressure is removed from a system, or the amount of outside atmosphere that flows through a pump. Usually, this is measured in standard cubic feet per minute (scfm). The significance of vacuum flow is that it determines the speed of evacuation of a system, or the ability to compensate for leakage in a system. As the level of vacuum (vacuum force) in a system increases, the flow rate decreases because there are fewer molecular impacts.

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FREE AIR CAPACITY The amount of outside atmosphere a vacuum pump can displace at 0 in.-Hg, or wide open. This expression is commonly used by vacuum pump manufacturers as an indicator of size and performance. It is confusing in that it does not tell us what type of performance to expect in a given range (level of vacuum force). Free air capacity is analogous to the size of an engine in a car; it is a starting point, but tells us very little about specific performance or efficiency.

VACUUM FORCE This term is most commonly defined as the level of pressure within a system, usually measured in inches of mercury. The amount of vacuum force created usually determines the lifting capacity of a suction cup or measures the amount of atmosphere left in a system. Vacuum force can not overcome porosity in a system, nor can it speed the evacuation time of a given volume. The higher the level of force, the longer it takes to achieve.

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Vacuum is typically divided into three areas of application, dependent upon the level of vacuum required.

Low level vacuum applications are typically those requiring high flows and low force (inches of mercury).

These applications are primarily serviced by blowers.

Screen printing on cloth is an application that falls into this range. in.-Hg. The largest number of applications occur here.

Vacuum in the industrial range can consist of anything from pick and place to thermoforming. The largest segScientific or process is an area that encompasses the deepest levels to 29.92 in.-Hg. Vacuum at this level is usually measured in torr. Flow in this range is minimal in transition from viscous to molecular. Examples of applications are ion implantation and space simulation.

The highest level of vacuum achievable on Earth is

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COMPRESSED AIR The energy source that drives an air-driven vacuum pump, measured in scfm. Compressed air is comparable to the electricity that runs a mechanical vacuum pump. Generated by an air compressor, and supplied through a network of piping at a certain pressure level.

AIR SUPPLY PRESSURE The pressure of the compressedair supplied, usually measured in psi. The measurement used to determine the optimal operating pressure of an air driven vacuum pump. Optimal pressure is obtaining a balance of supply pressure and air consumption to achieve the maximum efficiency level.

29.92 in.-Hg. A perfect vacuum (30 in.-Hg)—a space that contains no molecules or atoms—is purely theoretical.

EVACUATION TIME

The only possible place where this condition can exist is

The amount of time it takes to evacuate a given volume to a desired level of vacuum.

in space and, even there, a few atoms can be found.

HANDBOOK

ment is in the 12 to 21 in.-Hg range.

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Industrial vacuum falls within the range of 6 to 29.5

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ENERGY CONSUMPTION The amount of energy, whether expressed in hp, kW, scfm or any other expression, that a vacuum pump uses to generate a desired amount of vacuum.

LIFTING FORCE The lifting capacity of a suction cup, determined by multiplying pressure times the area.

VOLUME The total of all area in a vacuum system from the interior of the pump to, and including, the area of application.

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Pneumatic

VALVES COMPRESSED HANDBOOK

air pneumatic systems require methods of safe and precise control of the actuators unique to their accoutrement. Although the medium is fluid, just as hydraulic or process water systems, the execution of control is different in many ways than with a liquid. What is shared in the conduction of any fluid power medium is the need for valves to control force, velocity and direction of movement.

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AIR PREPARATION Pressure relief valves will control pressure at their inlet port by exhausting pressure to atmosphere.

Relief valves are typically used only in receivers or air storage devices, such as accumulators, as a means to prevent excessive pressurization. As such, relief valves are often called safety valves and are not typically appropriate for use anywhere but the air preparation stage.

Pressure regulators in pneumatic systems limit pressure downstream of the unit by blocking pressure upstream at the inlet. Regulators are used in the air preparation stage, as well as in control of cylinders and motors. The letter R in the acronym FRL stands for regulator, which is installed downstream of the receiver tank, but before the circuit they are regulating pressure for.

Sometimes multiple stages of pressure reduction are required, especially with a large centralized compressor and receiver feeding various workstations. A regulator can control pressure within the main grid of distribution plumbing, but sometimes

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air is piped directly to an FRL at each workstation or machine. Pressure at this main header could be 120 psi or more, but a branch circuit could be regulated at 90 psi, for example. Most regulators are capable of relieving downstream pressure, which prevents that downstream pressure from elevating as a result of load-induced pressure or thermal expansion.

Pressure regulators can be had as stand-alone units, but sometimes a filter is attached to kill two birds with one stone. Regulators are most often available as a component of a modular set, with a filter, regulator, lubricator or dryer, and can be assembled in any combination. The regulator will have an inlet port, outlet port and a port for the pressure gauge, with which they are most often included.

Pressure regulators can also be used to control pressure for individual actuators, such as an inline regulator or work-port mounted regulator. These are typically quite small and included with reverse flow check valves, as would be required for double-acting function of a cylinder, for example. Further still, differential pressure regulators are offered by some manufacturers to maintain a set pressure differential between the two ports, rather than just maintaining downstream pressure. It should be noted that all pressure regulators are adjustable, most often with screws or knobs.

FLOW CONTROLS Also common in pneumatic systems are valves to control flow. There are fewer available types of flow valves compared to pressure or directional fluidpowerworld.com

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PNEUMATIC VALVES

valves, but most circuits apply them to make for easy adjustment to cylinder or motor velocity. Controlling velocity in pneumatic systems is more complex than in a hydraulic system because pressure differential between the work ports of a cylinder plays a larger part.

Flow control valves for pneumatic systems are quite simple, usually available in two configurations used in two different ways. One configuration is merely a variable restriction, with a screw or knob adjustment to open and close a variable orifice, which is also often referred to as a needle or choke valve. The other type introduces a check valve, which allows free flow in one direction and restriction in the opposing direction. For whatever reason, this valve has hijacked the name flow control all for itself.

Flow control valves are applied in two different ways: meter in or meter out. Meter in is the method of controlling the rate of airflow as it enters a motor or cylinder. When metering in, a cylinder will move rapidly with high force and efficiency, but the motion of the piston is prone to spongy and unpredictable movement. When metering out, the cylinder velocity is more stable and repeatable, but efficiency and dynamic force are lost to the energy required to push past the flow control. Regardless, most pneumatic applications operate using meter-out flow controls because the disadvantages are easy to overcome by increasing upstream pressure.

A method of increasing cylinder velocity, typically for double-acting or spring-return cylinder retraction functions, is to add a quick exhaust valve to the cap side work port. Because cylinders retract faster than they extend as a result of differential air volumes, it is harder to evacuate the cap side air volume without oversized valves or plumbing. A quick exhaust valve vents directly to air from the cap side work port and massively reduces the backpressure created upon retraction, permitting rapid piston velocity.

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DIRECTIONAL CONTROL VALVES Pneumatic directional valves are available in many sizes, styles and configurations. At the basic end of the spectrum is the simple check valve, which allows free flow in one direction and prevents flow in the reverse direction. These can be installed anywhere from right after the receiver to within a flow control valve itself.

As directional valves grow in complexity, they are specified under a general naming practice related to the number of positional envelopes of the valve and the number of work ports in the valve, and specifically in the order described. For example, if it has five ports, port 1 will be for pressure inlet, ports 2 and 4 for work ports, and 3 and 5 for the exhaust ports. A valve with three positions will have a neutral condition, extend condition and fluidpowerworld.com

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PNEUMATIC VALVES

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pilot operated. Low-end valves consist of only a spool and body, and are prone to internal leakage. Better valves use seals in the body or spool to prevent leakage between ports. High-end spool valves are constructed with precision, often requiring fine lapping procedures during manufacturing, and with their tight tolerances, often require few seals, improving reliability and longevity. Other forms of high-end valves use a sliding block of metal or ceramic, which is not only efficient, but also extremely resistant to contamination, making them great for dirty environments.

retract condition. Putting it all together, this describes a five-way, three-position valve, also referred to as a 5/3 valve. The common configurations seen in pneumatics are 5/3, 5/2, 4/2, 3/2 and sometimes 2/2 valves.

Also part of the description of a directional valve is its method of both operation and positioning. The valve operator is the mechanism providing the force to shift the valve between its positions.

The operator can be a manual lever, electric solenoid, air pilot or cam mechanism, to name a few. Some valves are a combination of these, such as a solenoid pilot valve, which is a tiny valve providing pilot energy to move the main-stage valve. Positioning of any valve is achieved by either a spring, such as with a 5/2 spring-offset valve, or with detents, as in 5/2 detented valves.

A 5/2 spring-offset valve will return to its starting position when energy is removed from its operator, like deenergizing the coil, or removing pilot pressure. A 5/2 detented valve will stay in the position it was last activated to until the operator switches it again.

Pneumatic valves are manufactured in various incarnations. Poppet valves are simple, using a spring to push a face of the poppet down on its seat. Construction can be metal-to-metal, rubber-to-metal or even with diaphragms. Poppet valves can often flow in one direction, just as a check valve, but need to be energized to flow in reverse. They are limited to two- or threeway port configurations, although they can mimic four- or five-way valves when used in parallel. They offer typically high flow conductance for their size, and are generally resistant to contamination.

Spool valves use a notched metal cylinder that slides within a precisely machined body, drilled with three to five ports, or even seven ports if the valve is FLUID POWER WORLD

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MOUNTING CONSIDERATIONS Pneumatic directional valves come in both standard and non-standard mounting configurations. The nonstandard valve is constructed at the whim of the manufacturer, with port layout, operator style and mounting options unique to their product. They can be inline, subplate mounted or sectional stacks mounted in a row. Because each manufacturer does mounting differently, it is best to research the product appropriate for your application.

Luckily, most manufacturers have lines of standardized valves suiting one or more specification, such as ISO 5599-1, with its staggered oval ports; this means one manufacturer’s valve will fit the subplate or manifold of another manufacturer’s.

Port and electrical connections are standardized with most valves as well.

NPT ports are common, but many new valves come with push lock fittings on the subplate itself. Electrical connectors for standardized valves are frequently DIN, mini-DIN or with field bus connection, making the operation of a dozen valves as easy as one connector.

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Hydraulics

OVERVIEW HYDRAULIC

technology has been around in one form or another for thousands of years. Water has been used to irrigate and control water clocks, turn waterwheels to mill flour or grind wood into pulp.

Modern hydraulic systems continue to flourish, as they have one particularly important thing going for them: power density. No other technology can match the pure brute force of hydraulic oil (often at pressures approaching 3,000 and 5,000 psi, or even much higher) and do it in a reasonable amount of space.

That’s why we see hydraulics at work in some of today’s most demanding applications, from the Caterpillar equipment building our roads and cities to the John Deere equipment servicing our farmlands and the Komatsu equipment harvesting the raw materials from our mines. That’s not to say that hydraulics can’t be precise, however. You will find the technology on passenger airliners and military jets, as well as on machine tools and material handling equipment.

Hydraulics differs from pneumatics in that the medium being used to transmit power is a liquid as opposed to a gas. The liquid

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is generally hydraulic fluid, which is based on a mineral oil base stock. In some cases, water can be used—but this requires the use of specialized components and is not altogether common.

Hydraulic fluid has low compressibility (or a high bulk modulus) and generally a good thermal capacity.

Naysayers may argue that hydraulics is a dirty, loud and even an environmentally unfriendly technology. However, that lazy argument doesn’t ring true for fluid power engineers. Those claims merely indicate that the systems being described are improperly designed, installed or maintained.

Understanding the operation of and parameters for the application is critical, as is a good working knowledge of sealing and how to deal with contamination. Even something as basic as adding a new component to a sealed hydraulic system can introduce contamination—something that leads to eventual systemic breakdown. The bottom line is that, as in any industrial system, smart engineering design and regular maintenance will avoid problems in the future.

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Hydraulic

ACCUMULATORS

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ACCUMULATORS

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are pressure vessels that store hydraulic energy and deliver that energy back to the system on demand. This is analogous to the way a car battery or electronic capacitor stores energy. In hydro-pneumatic accumulators, compressible gas (nitrogen) is used to keep stored fluid pressurized, and the re-expansion of the gas is what supplies the energy back into the system. Hydro-pneumatic accumulators are used extensively in the global fluid power industry.

In industrial plant operations, accumulators suit multiple purposes: pulsation dampeners, emergency power source, thermal expansion, transfer barrier for fluid separation, as prefill for large volume press applications, noise attenuation, leakage compensators, dispensers for pressurized lubricants, auxiliary power and others.

There are three primary designs of accumulators, each employing a different method to separate gas from liquid. Bladder accumulators use a flexible closed bladder inside a forged steel shell. Diaphragm accumulators use a flexible open diaphragm (membrane) separating two steel clam-shells either welded or threaded together. Piston accumulators consist of a moveable hydraulic piston within a sealed tube and soft seals on the piston to separate liquid from air.

For high-pressure bladder accumulators, seamless chrome-moly steel has been used extensively for more than 40 years. This material has a high tensile strength, which must withstand the massive load exerted by hydraulic pressure. The material lends itself well to forming and machining and has a burst pressure more than 350% of design pressure, also considered a 3.5:1 safety factor conforming to ASME Code.

Various coatings can enhance resistance to rust, corrosion and abrasion to the accumulator finish. Most notably is the internal coating of phenolic resins, which is a material providing excellent resistance to many common process fluids and has shown excellent chemical resistance. It is easily applied, and for bladder accumulators, aids in applications where lubrication from the working fluid is poor. Because of the smooth surface, it helps prevent the bladder from adhering to the internal wall surface during operation.

Electro-less nickel plating is also very popular, which is a coating applied approximately 2-mm thick, internally and externally. Electro-less nickel has proven to be a durable and cost-effective material. It has also been shown to be a viable alternative to the significantly more costly stainless steels, while maintaining the strength integrity of carbon steel. The nickel plating variation, as with the phenolic

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coated cousin, can be combined with 316 stainless steel connections. These connections include the liquid and gas ends of the accumulator, along with the all internal component parts. A bonus quality of nickel plating is that it protects the accumulator on the outside, for those applications where water washdown or corrosive vapors may be present. Electrolytic action between the stainless steel and electro-less nickel is seldom seen.

There are several accumulator manufacturers who produce accumulator housings using 316 stainless steel; however, because 316 stainless steel does not have the tensile strength of high carbon steels, the wall thickness must be increased to improve pressure capacity, especially for accumulator designs seeing greater than 500 psi maximum allowable working pressure.

Stainless-steel hydraulic accumulators are usually special ordered, both in the piston and bladder configurations, and therefore may have extended delivery times.

The most common and most widely used of all accumulators are for the fluid power market. Hydropneumatic accumulators are sometimes designed to

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HYDRAULIC ACCUMULATORS

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operate up to 6,000 psi, although 3,000 psi or less are more common. Both piston and bladder accumulator manufacturers provide the fluid power industry with variations from 1.5 in.3 of volume up to 120-gal capacity.

These are the most common accumulators selected by OEM manufacturers for injection molding machines, rubber processing machines, die casting machines, machine tools, presses, and a variety of automated machines and process lines with extensive use in the land-based and offshore oil industry for safety valves and production applications. Another classification of accumulator is of the 500-psi bladder design, which offers large-capacity, up to 140 gal and larger. These bladder accumulators are most commonly found in process areas where large piping networks are distributed through one or several buildings. These networks carry a variety of fluids, such as water, fuel oil, lubricants and chemicals.

These accumulators are sized and placed in specific locations to primarily eliminate shock. Secondary applications of these large capacity accumulators are for thermal expansion/contraction, pump start up and

SIZING ACCUMULATORS

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Whereas:

commercial piping connections, from 150

element of reliability. One must size the

P1 = Initial Pressure

to 600 lb. For high-pressure accumulators—

accumulator according to the application,

V1 = Initial Volume

piston, diaphragm or bladder—the choices

taking into consideration flow rate, maximum

P2 = Final Pressure

are female NPT, SAE, BSP or Code 61/62

operating temperature, maximum and

V2 = Final Volume

flange connections.

Properly sizing the accumulator is the first

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shut down, and for fire protection.

Smaller accumulators, known as the diaphragm type, are mostly used for pulsation dampening where flow rates are relatively low. These accumulators are usually non-repairable and must be disposed of when wear or failure occurs; however, repairable diaphragm accumulators are now more common from some manufacturers. The diaphragm accumulator is a relatively low cost device, rated up to 10,000 psi, but can be used on low-pressure applications as well. They are very reliable products, and with proper precharge and maintenance, their reliability will be further extended. Diaphragm accumulators may be phenolic coated internally or coated internally and externally with electro-less nickel plating, just as with other accumulators. They also have optional elastomers for specific fluid compatibility.

Some manufacturers offer these in 316 stainless steel housings at reduced operating pressures. The design is simple— they feature the anti-extrusion plug built into the bladder and with the repairable design, bladders can be replaced in minutes.

minimum pressures, and of course fluid

After correctly sizing the accumulator for

Finally, accumulator precharge must be

compatibility. Boyle’s Law of Gases is the

its particular application, materials must

selected, which is typically 90% of maximum

primary formula for sizing. Specific formulas,

be properly chosen for compatibility.

working pressure. This allows the highest

depending on the application, expand

Appropriate seal technology is chosen

expansion ratio and gets the most out of the accumulator volume. When precharge is too

from the primary formula shown below.

depending on the fluid and the operating

Compression of gas, temperature and cycle

temperature. From there, connection sizes

low, the accumulator can only provide energy

times are factored in the expanded formulas.

are chosen based on flow rate required,

when system pressure drops very low. When

P1V1 = P2V2

with a host of options: for the large, 500-

precharge is too high, hydraulic fluid will

psi bladder accumulators, normally the

never enter the accumulator, and no energy

standard ANSI flanges are chosen, based on

will ever be stored.

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BAR STOCK BAR STOCK

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subplate mounts. The subplates allow one valve to mount atop, with four ports on each of the four sides. Bottom ported subplates are also available, but are rarely used. Bar manifolds have plenty of material to enable the addition of a relief valve cavity, but subplates have no such luxury of real estate. Both manifolds and subplates are available in sizes from D02 to D08, and many manifold accessories are available to help complete the hydraulic circuit, such as tapping plates, cover plates and gauge blocks.

Bar stock can also be used to clean up plumbing on machines by reducing the need for adapters and fittings. By drilling ports into a bar, a header or manifold can provide a junction to common feed or return lines, so that each tube or hose plumbs neatly into the same source. Manifolds and headers can reduce leak points, but also add a look of professionalism compared to a mess of tees and adapters. Bar stock is great for mounting components, such as test points, transducers or pressure switches. The bar material can also be anodized any color, or even just treated for corrosion resistance by clear anodizing for aluminum or nickel plating for ductile iron. Lastly, because bar stock is so commonly used in various applications, it is readily available through every fluid power distributor in North America.

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is used in various applications of fluid power, either as a mounting for other valve systems or simply for consolidation of plumbing.

The bar stock itself is typically an alloy of either aluminum or ductile iron, and is manufactured in billets suitable for machining finished product. The most popular use is the bar stock manifold, which is a block of varying length drilled with passages, ports and bolt holes for mounting valve systems.

Aluminum is a popular choice for bar stock material when system pressure is 3,000 psi or less. Aluminum is easier to work with than ductile iron, and is lower in physical mass and overall cost. However, when working pressure is higher than 3,000 psi, iron is required to withstand the additional stress.

Ductile iron is a cast alloy that is less brittle than standard cast iron, and is less expensive than steel; although forged steel is another option for bar stock, it is rarely used on less than the most extreme applications.

Whatever name you known them by best—ISO, cetop, NG6, D03 and so on—the industry standard modular stackable valves are the most common system of circuit construction, and they all require a manifold to interface with. A manifold for a D03 valve, for example, is around 3-in. tall and 3-in. deep, but can be as long as needed to mount any number of valve stacks.

The manifold most often has pressure and tank drillings running its length. Each “station” of the manifold, where the valve mounts with four bolts, has four drillings mating up with the pressure and tank passages, as well as mating up with the work ports, which are drilled on the side of the manifold in a vertical arrangement. Bar stock manifolds can be drilled as either parallel or series circuits, depending on the application.

Bar stock can be cut into smaller slices and drilled in similar arrangements to bar manifolds to create

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CLUTCHES & BRAKES HYDRAULIC CLUTCHES A clutch is a device used to transmit mechanical power from a prime mover (electric motor or internal combustion engine) to a transmission or driven device.

As opposed to a mechanical clutch, a hydraulic clutch uses a fluid coupling device to transmit rotational power at variable operating speeds and without problems of shock loads. The fluid coupling device contains a driving turbine, or torus, also known as the pump, which creates flow within the chambers of the fluid coupling enclosure. This flow drives the output turbine, which is connected to the driven member of the transmission system.

Clutches have found use in industrial, automotive, railway, airline and agricultural settings. When selecting a hydraulic clutch, important criteria to consider include what applications, performance specifications and compatibility are desired.

The performance of a hydraulic clutch can be broadly specified according to its torque rating, power, rotational speed and maximum pressure. The maximum torque is the greatest rated torque the clutch drive can bear, and is typically the limited factor in most applications. The maximum power capacity refers to the operating power of the load the clutch is intended to operate under, which is a factor of torque and speed. Rotary speed is the intended operating speed that the clutch has been designed to rotate at, while the maximum pressure is the greatest pressure that the clutch can withstand.

When considering compatibility of the clutch with driving and driven members, the clutch dimensions, clutch shaft geometry and drive connection type are important considerations.

Significant clutch shaft dimensions are bore diameter, clutch diameter, length and weight. Clutch shaft geometry can be in-line, parallel, right angle or another arrangement. The connection type of the clutch shaft can be in-line, through shaft or flanged at the ends.

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systems by converting kinetic energy into heat energy. When triggered, they transfer pressure through the use of a fluid and this pressure triggers the braking mechanism by pushing on a piston in a brake caliper or slave cylinder.

These braking mechanisms consist of brake types such as drum brakes, disk brakes, band brakes and cone brakes.

Each of these braking styles have different braking properties, but they are all powered, by way of hydraulic fluid, from the pressure of a master cylinder or pump. The main specifications considered with brakes are speed, power, torque and maximum pressure.

When selecting a brake, the style of braking is the first choice an engineer must decide on. Drum brakes work by applying hydraulic pressure, pushing a braking pad or shoe against the rotating surface, creating friction and slowing the spinning surface down.

Disk brakes function by squeezing the rotor with calipers to slow it down.

Band brakes work by tightening the band material around the rotating drum, similar to older stationary bikes.

A cone brake works by forcing two cone-shaped devices toward each other, one of which is the rotor and the other is the friction material.

COMBINATION PACKAGES Because hydraulic brake and clutch components both use fluid power, they can be integrated and manufactured for ease of compatibility and installment into the application. When both clutch and brake components are present, braking can be facilitated by the disengagement of the clutch mechanism, which transmits the power needed to apply the brakes.

FPW

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Hydraulic

HANDBOOK

CYLINDERS

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cylinders are at work in both industrial applications (hydraulic presses, cranes, forges and packaging machines) and mobile applications (agricultural machines, construction equipment and marine equipment). When compared with pneumatic, mechanical or electric systems, hydraulics can be simpler, more durable and also offer greater power density. For example, a hydraulic cylinder has about ten times the power density of an electric linear actuator of similar size. Hydraulic cylinders are also available in an impressive array of scales to meet a wide range of application needs.

Selecting the right cylinder for an application is critical to attaining maximum performance and reliability, which means taking into consideration several design and performance parameters. Fortunately, an assortment of cylinder types, mounting methods and “rules of thumb” are available to help select the appropriate cylinder.

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WHAT IS THE MAXIMUM PRESSURE FOR THE APPLICATION? The hydraulic cylinder must be rated to work within pressure limit of the hydraulic system it is installed on. An excavator, for example, can operate at 4,000 psi or more, so light-duty snap-ring cylinders rated for 2,000 psi should be avoided.

Cylinders are designed with safety factors of 2:1 to 4:1, so sometimes running slightly over-limit might be acceptable, but not double.

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FOR ALL YOUR

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MOBILE HYDRAULIC SOLUTIONS

CYLINDER MOUNTING METHODS Mounting methods also play an important role in a cylinder’s performance. Generally, fixed mounts on the centerline of the cylinder are best for straight line force transfer, ideal column loading and avoiding excessive wear.

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requires either a spring or mass to retract.

For all types of cylinders, the critical measurements include stroke length and bore and rod diameter. Stroke lengths vary from less than an inch to several feet or more, depending on the requirement of the machine. Bore diameters can range from 1 in. up to more than 24 in., and piston rod diameters range from 1/2 in. to more than 20 in. In practice, however, the choice of stroke, bore and rod dimensions may be limited by environmental or design conditions.

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HYDRAULIC CYLINDERS

CYLINDER TYPES The three most common types of cylinders are tie-rod, welded and ram, the latter of which is single acting, meaning it is powered in one direction only. Tie-rod cylinders can be single acting, although they are most often powered in both directions. They have machined, square caps and heads being forced together against the barrel by high-tensile steel tie rods fastened by nuts, making them easy to disassemble and repair in the field. Welded cylinders employ a steel barrel with a cap welded to the bottom and the end treatment subsequently welded to the cap. The rod and piston assembly then has to be assembled around the head—which uses a buttress thread for strength—and is tightened into the barrel. Finally, the single-acting ram is typically just a rod inside a barrel with a single port and

FP

HANDBOOK

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NSID

WHAT STROKE LENGTH WILL BE REQUIRED? This is fairly straightforward, but it should be ensured that the machine has appropriate clearance, because the longer retracted length of the cylinder should be factored. Also, if stroke is too long, additional support will be required, such as a guided load or stop tube.

WHAT MOUNTING METHOD IS BEING USED? Flange mounting is often the best solution because the load is transferred along the centerline of the cylinder. Non-centerline mounting calls for additional support to avoid misalignment, but these are required when the mechanism must pivot through an arc, so load calculations must be factored accurately.

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KEY SPECIFICATIONS:

hydraulic systems use

design specification, such as force,

a form of mineral oil,

maximum pressure and mounting con-

but applications using

figuration, but consideration for oper-

toxic synthetic fluids—such

ating conditions must also be heeded.

as phosphate esters—require

Cylinders must also withstand extreme

Viton seals, which will not break down

temperatures, humidity and even salt

or swell in the fluid. Once again,

water for marine hydraulic systems.

Buna-N seals may not be adequate

Also, when ambient temperatures rise

to handle some synthetic hydraulic

to more than 300° F, standard Buna-N

fluid, although the gentler synthetics,

nitrile rubber seals may fail and will

such as PAO-based stock, will be fine.

instead require synthetic rubber seals,

Hydraulic systems using high water-

such as Viton. When in doubt, err on

based fluids may require stainless-

the safe side and choose a cylinder

steel construction, as well as PTFE

design capable of more of than you

(Teflon) seals, especially if no glycol is

will ask of it.

used in the fluid.

COMMON TYPES OF MOUNTING INCLUDE: Flange mounts—Strong and rigid, but have little tolerance for misalignment. It is recommended to use cap end mounts for thrust loads and rod end mounts for loads under tension.

Side-mounted cylinders—Easy to install and service, but the mounts can sometimes create a bending moment as the cylinder applies force to a load, increasing wear and tear. To avoid this, specify a stroke at least as long as the bore size for side mount cylinders (heavy loading tends to make short stroke, large bore cylinders unstable). Side mounts, such as side

HANDBOOK

Fluid type—Most

must meet the requirements of the

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Operating conditions—Cylinders

Pivoting mounts, such as clevis or trunnion, require care in application, because of their capacity to move as the cylinder is stroked, resulting in a possible bent rod or excessive wear.

HYDRAULIC CYLINDERS

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lugs, need to be well aligned and the load supported and guided.

Centerline lug mounts—Absorb forces on the centerline, but require dowel pins to secure the lugs to prevent movement at higher pressures or as a result of shock loads.

Pivot mounts—Absorb force on the cylinder centerline and let the cylinder change alignment in one plane. Common types include clevises, trunnion mounts and spherical bearings. Because these mounts allow a cylinder to pivot, they should be used with rod-end attachments that also pivot. Pivoting mounts are required for many applications, such as booms and buckets, but are also most prone to rod buckling, especially as the rod reaches end of stroke.

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PUSH OR PULL OR BOTH?

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Any cylinder can be used as single acting, which is powered in one direction only, but this means they can either push or pull, not both. When a cylinder pushes, protection against rod buckling and bending must be ensured, which can be achieved through oversized rod material or with a stop tube to prevent full extension, taking advantage of the load-bearing effect provided by the piston. When a cylinder pulls, there is little concern for buckling, but you should ensure your force calculations factored the smaller rod side of the piston, which experiences reduced force compared to the cap side of the piston. A double acting cylinder is powered in both direction to push and pull.

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KEY SPECIFICATIONS CONTINUED: Seals—Seals are the most vulnerable component of a hydraulic system.

Properly chosen and applied seals can

COFFEE or

TEA?

You also have a choice for hydraulic cylinder positioning

reduce friction and wear, lengthening service life, while the incorrect type of seal can lead to downtime and maintenance headaches as a result of failures. Every manufacturer likes to use a different seal style, so it is important to replace them with a similar type and

Miniature Mounting

Non Contact Operation

Inside the cylinder?

Signal Electronics Built Inside

material when rebuilding.

• Compact, robust design

Cylinder materials—The type of metal

• Maintains ASAE pin dimensions

used for cylinder head, cap and bearAbsolute Signal

ing can make a significant difference in performance and reliability. Most cylinders use bronze for rod bearings

• Excellent *vibration capablity

Short Length Maintains Pin to Pin Dimensions

and medium-grade carbon steel for

*Tested to Mil-STD-202G

heads and bases, which is adequate for most applications. But stronger materials, such as 65-45-12 ductile iron for rod bearings, can provide a sizable performance advantage for

No Extra End Cap Costs

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Or outside the cylinder?

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tough industrial tasks. The type of

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piston rod material can be important

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in wet or high-humidity environments (like marine hydraulics) where stainless

• Ideal for steering cylinders

steel may be more durable than the standard case-hardened carbon steel with chrome plating used for most

No Deep Drilling Costs

Maintains Piston Rod and End Cap Strength

• Ideal for long cylinders up to 130 ft.

piston rods. A new option for rod surface treatment is nitriding, which is an oxidation process to increase the surface hardness of metals, and in the case of cylinders, makes for excellent corrosion resistance.

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WHAT PUSH OR PULL TONNAGE IS REQUIRED? Always assume peak loads will require additional strength.

The rule of thumb is to choose a cylinder with a tonnage rating of 20% more than required for the load; however, this is always application-specific, so it’s best to consult a hydraulic professional before you make tonnage assumptions. Cylinder force (lb) is equal to the area of the piston (in.³) times pressure (psi), or F=AxP.

MS2 — Foot Side Lugs

MS7 — End Lugs

MF2 — Cap Rectangular Flange

MF6 — Cap Square Flange

FP

HANDBOOK

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MF5 — Head Square Flange

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Hydraulic

FILTERS MANY

FP HANDBOOK

fluid power systems fail simply because there is too much contamination in the medium. In fact, some estimate that 75% of all fluid power failures can be attributed to contamination issues. Thus, an engineer who ignores filtration does so at the peril of his/her system.

There are multiple reasons why fluid can become contaminated. Use and wear of the components, poor plumbing and contamination brought in with new fluid (or new components) are just a few of the possibilities. This is why no fluid power system can be complete without the use of a filter. Hydraulic filters keep the hydraulic fluid contaminant free.

Because of the dependence of the fluid power system on a filter, they can be found in many applications. Some of these include construction vehicles, factory equipment and even oil rigs.

There are several types of filters, including bag, screen and magnetic. The bag filter consists of a cloth bag in which the hydraulic fluid is pushed through; the contaminants (being solid) are unable to flow through the bag as easily as the fluid. This is particularly useful in the filtering of dirt, rust and particles introduced into the system by a cylinder rod. Screen filters are constructed with many small wires that are woven together to create a metallic cloth. These filters can be constructed to a precise pore size, which allows an engineer to choose the right size for the expected contaminant size. Finally, there are magnetic filters, which use magnetically charged plates that will attract any metallic contaminants in the system.

The construction of the filter is also an important selection criteria. This covers what is included with the filter and the alignment. When purchasing a filter it is important to know if

SELECTION CRITERIA • Flow describes how much fluid flow is permissible through the filter, the maximum flow rate.

• Pressure describes the maximum operating pressure that the filter can withstand.

HYDRAULIC FILTER cutaway shows filter elements, end caps, support tube, inner and outer screens, and different depth layers.

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• Port size is the size of the inlet and outlet ports that need to connect to the hydraulic fluid system.

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HYDRAULIC FILTERS

HANDBOOK

Filtration & Fluid Management Sensors & Measurement Fluid & Motion Control

FP

Sensors & Measurement

ARGO-HYTOS Inc. 1835 North Research Drive · Bowling Green, Ohio 43402 Phone: + 419-353-6070 · Fax + 419-354-3496 info.us@argo-hytos.com · www.argo-hytos.com 72

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HYDRAULIC FILTERS

FP HANDBOOK

the system needs a filter with or without the housing. It is also possible to just purchase a filter element and replace that section of the filter. There are a few different alignment options available for filters. When the inlet, outlet and filter are all lined up, it is called an “in-line” alignment. Another alignment is the “off-line” alignment, which is when the filter is not on the main hydraulic system’s loop. There is another configuration which is called “duplex.” This configuration is when two filters are combined together. These filters are useful for maintenance (changing of the filter elements) without disrupting the working system.

A “return-line” configuration is designed to catch all contaminants introduced to the system through its various parts. It is thus named because it is the last element in the system and placed in the return line for the fluids to the tank.

A filter’s rating is a measure of its effectiveness.

One of these, ISO 4406, is a standard measure of the contaminant level found in a given filter system. An ISO 4406 code is composed of two to three numbers, each of which represents a logarithmic measure of the number of contaminants present at three set size ranges (4µ, 6µ, 14µ[c]) in 1 mL of fluid. For example, a new sample of oil might measure 18/15. This corresponds to 1,300 to 2,500 particles of 4 µm, and 160 to 320 particles greater than 14 µm. A filter with a lower ISO cleanliness rating will therefore more thoroughly remove contaminants and can help to prolong the life of the hydraulic system’s components by 2 to 3 times.

Another measure of filter efficiency is the filter’s beta ratio, which is the ratio of the number of contaminant particles upstream of the filter divided by the number downstream.

The beta ratio can be subtracted by 1, divided by the beta ratio and multiplied by 100 to obtain the filter’s percent efficiency for a given contaminant size. When choosing a hydraulic filter, a greater beta ratio is desirable.

ISO CODES.

RIGHT ON TARGET. hyprofiltration.com/

FPW

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Filtration

SYSTEMS

SOMETIMES,

FP

HANDBOOK

inline hydraulic filters are not enough to keep a hydraulic system functioning properly. Most hydraulic systems are installed with at least a return filter, which semi-purifies fluid before it is once again welcomed into the reservoir. However, what if a single return filter is not enough? What if your cleanliness codes are not achieved, even if you’ve upgraded to a finer filter media? A pressure filter is an option, which will keep the components downstream of the element one step cleaner. But what if using a pressure filter is impossible, due to plumbing difficulties or pressure drop considerations?

A solid option to increase filtration effectiveness is with an offline filter system, often called kidney loop filters. Offline filtration uses a dedicated lower pressure pump (still often a hydraulic pump), which draws fluid from the reservoir and then flows that fluid through a dedicated filter assembly— usually of a high-quality medium—and then right back into the tank.

Sometimes hydraulic power units have dedicated offline filter systems, whose only jobs are to circulate fluid from their reservoirs and filter it as it does so. Because a kidney loop filter neither affects nor is affected by the main hydraulic system, it is a consistent and stable way to keep the oil clean. The pressure drop of often low-micron filter media will never be additive to system pressure drop, especially those related to flow surges in the tank lines of machines with rapid cycle times of cylinders. It is not uncommon to see 5- or even 3-μm offline filters with high beta ratios.

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Know What’s Running Through Your Equipment.

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Filtration_FP_June_Vs6.indd 76

Offline filtration also enables changing of filter elements while the machine is running, as shutting down the kidney loop has no association with machine operation. Some filtration systems employ duplex filters, which are two filter assemblies installed in parallel, separated by a three-way ball-valve. This design allows for live selection of either filter so the other can be replaced. Most filter manufacturers offer a filter system dedicated to the offline filtration market that is highly efficient and offers high dirt holding capacity.

Offline filtration is typically the highest quality in a manufacturer’s product line, which is reflected in the cost of these products. To help justify the purchase of such a system, they are often sold as portable units, small units that can be carried by a handle, or large units requiring a wheeled cart to manage their bulk. These units can be wheeled from machine to machine, where a suction tube is placed into a port of the reservoir and then passes through its own filters before being injected back into the tank.

Depending on the size of the tank, the filter system’s flow rate and filter quality, one might leave the filter system running on the machine for hours or perhaps days.

Some of these filter systems are installed with auxiliary electronics, such as particle counters. A particle counter will give you a live reading of the ISO Code of the oil passing through the unit, so you can leave the unit running until the desired code is achieved. If this type of system seems out of your reach, note that some hydraulic distributors will rent these machines out for a reasonable cost.

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Hydraulic

FITTINGS & FLANGES HYDRAULIC

help identify each standard to confirm diameter and thread type.

Fitting connection types include: welded (socket weld, butt weld, slip on); threaded (NPTF, BSPT [both not recommended but used], SAE straight thread, ISO 6149; BSPP); flanged; barbed; quick-disconnect; pushto-connect; 37˚ flare; 24˚ cone; and inverted flare, among others. When selecting a type of fitting, some important considerations are working pressure, vibration, type of fitting, desired attachment, size of piping, flow, material of the conductor or component, and price. The fluid power industry is trying to transition to fittings with an elastomeric seal—generally O-rings—to prevent leakage. These include, but are

FP

HANDBOOK

fittings connect tubes, pipes or hoses to components (pumps, valves, cylinders) or together to create a system through which hydraulic fluid under pressure can be transmitted without leaking. Fitting variations allow designers to change the direction of flow, split flows and change the elevation of lines to accommodate the location of the items they marry.

Fitting varieties include plugs, unions, elbows and crosses. Care needs to be taken in identifying the threads of the connections, as some connectors from one standard appear to thread into a different standard, but do not have enough thread engagement to be safe.

Documents from SAE, NFPA and ISO

HYDRAULIC FITTINGS are available in a variety of styles including elbows, crosses, tees and more. Common materials are steel, stainless, plastic and brass.

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® Switc h Your Swivel® Switch Your Swivel

TM

not limited to, the SAE straight thread, face seal, ISO 6149, and SAE J518 (Code 61 and Code 62) flanges. Seal construction must be compatible with the type of fluid being used in the system, although very few applications require anything other than Buna Nitrile or Viton.

When selecting a fitting, several considerations are important. Most non-flanged fittings have a gender, called male and female, that are joined together to form a union. Most fittings are sized based on the size of the conductor (size of hose, pipe or tube), and overall dimensions can vary greatly based on fitting type, even for the same size conductors.

Additionally, most fitting types are available in a multitude of materials, including plastic, brass, steel, stainless or specialty metals like Monel.

Each are applied in applications based on the fluid medium and ambient conditions, and each has different performance characteristics that allow customization within a fitting type. Often the first choice is to match the fitting to a similar material of the conductor or component that it is connecting to: plastic to plastic, steel to steel and stainless to stainless.

Geometry is also an important consideration, and geometry is typically identified by alphabet letters the fittings resemble. Fittings are available inline to change the direction of flow in various increments (45˚ or 90˚ elbows [L]), or a swivel to allow two joined sections to rotate. They can also split or combine flows with run and branch tees [T], “wahys” [Y] and crosses [+].

Fittings, particularly elbows, are offered in a variety of drop lengths, which is the distance from the centerline of one opening—called a port—to the end of the other port.

Fittings are available in various sizes to suit differing flow demands, and connection size is often expressed in dimensionless terms representing FLUID POWER WORLD

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THE LEADER IN TRACEABILITY BI Logo & Country

Date

Manufacturing Location

3 Digit ID Stamp

1st Gen 2nd Gen 3rd Gen 4th Gen

Gen 4 Traceability At Brennan Industries, we stand behind our products. That’s why we’ve developed an industry best, Gen 4 traceability program to ensure that every fitting we manufacture is BI logoed and has a fully traceable batch code.

Brennan’s quality and your peace of mind are assured by our product traceability program throughout the entire fitting’s life cycle.

To learn more: 888-331-1523 www.brennaninc.com © 2015 Brennan Industries, Inc.

ATLANTA • CLEVELAND • DALLAS • HOUSTON • LOS ANGELES • SEATTLE • SHANGHAI • TORONTO Brennan_FPH_6-15.indd 81

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⁄16 of an inch. For example, a -06 thread is 3⁄8 (6/16), and a “dash” 32 size is a 2-in.

(32/16) thread. A Y-flange may split a 2-in. flow into two reduced 11⁄2-in., instead of creating three 2-in. connections to more closely match the cross-sectional area.

O-ring face seal, SAE straight thread and ISO 6149 fittings have a seal, normally Buna N, contained within a groove to seal the fluid. It is important for the seal to be compatible with the fluid and the operating temperature range. An elastomeric seal greatly reduces the possibility of leakage caused by vibration, thermal cycling and pressure cycling.

SAE J518 split flange fittings are used on larger line sizes, starting at 1⁄2 in. (-8) but coming into predominance at 2 in. (-32) and above. A flange head with an O-ring groove on its face is attached to a conductor (hose, tube or pipe) and is secured to the port, which could be a flat-face fitting or a pad on a pump, valve or cylinder, by a clamp with four bolt holes. The clamp can be whole, but is often split so that a quarter of the diameter of the flange head is on either side of the centerline of the bolt holes to help minimize torque on the clamp. The screws used are tightened to a high torque value to avoid problems with fatigue. In many cases, using pipe or tubing, the flange connections have operated within their specified working pressure for decades.

Flare fittings, such as the JIC 37˚, are fittings with a conical end face and the seal is formed when this seat is forced against a mating seat, generally by torquing a swivel nut on one fitting, engaging with a threaded portion of the mating fitting. The angle of the seat and face for most JIC fittings in the North American market is 37°, and is popular enough that the 24° and 45° versions are rarely used. The fittings can be designed to clamp onto a tube by means of a sleeve or ferrule, and care needs to be taken so that the correct size is used because inch and metric tubing sometimes have sizes that are close to overlapping.

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HYDRAULIC

Flanges & Components

"Servicing Industry for over 50 years"

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HYDRAULIC FITTINGS & FLANGES

The quick disconnect allows multiple reconnections of the assembly without causing excess wear or concern for thread damage. Some fittings allow disconnection and reconnection under pressure; others do not. Disconnects hold fluid pressure by way of a ball or poppet, which is spring offset to remain closed when the lines are unattached. Upon reattachment, the balls or poppets push against each other, lifting themselves from their seats and allowing fluid flow. Standard plug and socket configurations, such as the Pioneer coupling, are prone to trapping contamination, which was addressed with the advent of flat-face couplers, which have no recess to collect contamination.

Staple and band fittings are low pressure fittings. Band fittings are attached to the hose by a barbed or beaded end being inserted into a hose and a band clamp securing the connection. This method is only for extremely low pressures. Staple fittings have a cylinder with an O-ring and a bead further up on it that slides into a socket. The connection is secured by a staple that goes through both sides of the connection behind the bead, although it is still typically used for low pressure or suction lines.

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"O" RING SEAL FACE OF PORT ON ADAPTER, PUMP, ETC. SPLIT FLANGE CLAMP HALF HARDENED WASHER - OPTIONAL METRIC OR INCH SCREW FLANGED HEAD FITTING

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SECTION Y-Y Y

Y

0.75 0.25

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SHAPE & SPLIT OPTIONAL

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THE QUALITY OPTION A complete and fully compatible hose and fittings non-skive system from R1AT 1/4” to R15 2” including wire braided, multispiral, thermo-plastic and teflon applications.

Intertraco (Italia) S.p.A. 46029 SUZZARA - ITALY info@intertraco.it www.intertraco.it

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Hydraulic

FLUIDS HYDRAULIC

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fluid is the energy transfer medium in all hydraulic systems.

However, the job of hydraulic fluid goes beyond simple transmission of power.

Although transmitting hydraulic energy is the core purpose of hydraulic fluid, it is useful in four secondary functions— heat transfer, contamination removal, sealing and lubrication.

Hydraulic machines produce a lot of excess heat in normal operation, often caused by inefficiencies of the components themselves, like pumps and motors. Without a way to carry heat away from these components, they could easily overheat with resulting damage of seals and internal components, especially as a result of low local viscosity. As oil returns to the reservoir, it often passes through a cooler to help maintain optimal temperature range before it is pumped back out to the system. Conversely, hydraulic fluid can carry heat into a system during cold starts when needed.

If closed-loop hydraulic systems didn’t bleed off fluid at a controlled rate, contamination would quickly accumulate to critical and damaging levels. Heat can be considered a form of contamination, but hydraulic fluid also carries particles and water away from sensitive components through filters or other conditioning devices, where it is cleaned up and returned to the circuit. Oil without impetus would remain within sensitive components, allowing essentially trapped contamination to slowly destroy its surroundings.

Although most believe hydraulic oil is what pieces of hardware—such as O-rings or

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U-cups—seal against, hydraulic fluid (especially oil) actually provides sealing within the internal components of pumps, valves and motors. A spool valve, for example, has a seal at each end to prevent oil from escaping the valve, but each notch on the spool is sealed from the neighboring cavities by only the tight metal-to-metal tolerances and the oil’s surface tension and resistance to shearing.

Lubrication is required in most hydraulic components to protect internal parts from wearing, or even downright melting, as a result of metalto-metal friction. Oil provides full-film lubrication between moving parts, such as the slippers and lens plate of a piston pump. Without the lubricating properties of oil, hydraulic systems would be inefficient and unreliable.

These functions of hydraulic fluid are common to all types, except some water-based fluids, which require special design considerations during engineering. However, the majority of machines use refined or synthetic oil, which are formulated and manufactured to specific test standards for important properties like viscosity, pour point and viscosity index, to name a few.

Those three properties are often considered when choosing a fluid for a particular application, which is based on maintaining a specific viscosity throughout a particular set of ambient and machine operating conditions. For example, if ambient temperatures are low, you would choose an oil with lower rated viscosity and a low pour point, which is the temperature at which oil will still pour. If your machine sees varying temperature ranges, like an all-weather mobile machine, a high viscosity index, fluidpowerworld.com

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HYDRAULIC FLUIDS

Quick & Simple PTO and g featherin e lv a v ir a

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which describes an oil’s ability to maintain its viscosity over a wide temperature range, is crucial.

It is important to consider the viscosity requirement of the components in your hydraulic system. A piston pump, for example, may require between 16 and 40 centistokes, which is a description of kinematic (measured while flowing) viscosity.

Hydraulic oil is engineered with other important properties, although these tend to be common regardless of brand, viscosity or application. Hydraulic oil has a package of chemical additives to improve the performance of both the oil and the components of the hydraulic system. These additives can improve the foaming resistance of the oil, its corrosion/rust resistance and the water-retention properties. The additive package of hydraulic fluid is what separates low- and high-quality fluids, and additives also improve the viscous properties of oil. When in doubt, always choose a premium fluid for your application at a viscosity appropriate for your operating conditions.

Installation

Installing the valve onto the seat bracket

Operating the P.T.O. and Dump Fully Installed

Supplied air is fed through the system’s pressure protection valve and a simple “T” from the air seat to the air valve.

Tel: 716.853.7996 • Fax: 716.853.8003 571 Howard Street, Buffalo, NY 14206 www.delhydraulics.com 6 • 2015

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Hydraulic

GRIPPERS are devices used with pick-andplace robotic systems to pick up or place an object on an assembly line, conveyor system or other automated system.

Fingered tooling (jaws) is attached to the grippers to grip or hold the object.

They come in a variety of styles and powered designs. Three common types are parallel, three-finger and angled designs. The most common are parallel designs, with two fingers that close on a workpiece to grip it or open it out by creating pressure on the inside. Threefinger designs hold the workpiece in the

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GRIPPERS

center, and have three fingers offset by 120°. Finally, angled designs feature jaws that work at a variety of different angle openings.

In addition, three choices of power are available; the most common being pneumatic grippers; electromechanical grippers are second most common; and the least common being hydraulic grippers. Hydraulic grippers are most often used in conjunction with a piece of equipment that only has a hydraulic power source for actuators.

Most hydraulic grippers are designed for a hydraulic system where the cylinder diameter is made with less surface area, meaning that a hydraulic gripper would have the same force at 60 bar as a pneumatic gripper of the same size at 6 bar.

In general, hydraulic and pneumatic grippers have the same basic

actuation principle. They include direct acting piston designs as well as piston wedge designs.

The direct acting piston design is used when a hydraulic force acts directly on a piston that is directly connected to the jaw or finger that is touching or gripping the part.

The piston wedge design features a hydraulic force acting on a piston while the piston itself is acting on a wedge. The wedge translates this force to the jaws or fingers, providing the grip force to grip the part. The wedge can give a mechanical advantage as it can increase grip force while keeping the piston diameter and pressure to the piston the same. This allows more grip force in a smaller package compared to the directing piston.

Unlike electromechanical grippers, which have motors on each actuator, one single motor powers the hydraulic fluid that supplies energy to multiple devices throughout a plant.

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WHEN SELECTING A HYDRAULIC GRIPPER, IT IS IMPORTANT TO CONSIDER THE FOLLOWING: • Part weight and size to be lifted • Part material • Clearance issues around the part that could interfere with the gripping part • The environment the gripper will be used in (corrosive, food or beverage, and so on) • The motion path of the robot or linear device that is moving the gripper • The power supply that will be available and the pressure ratings available

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© 2014 SCHUNK GmbH & Co. KG

90 %

SWS Quick-Change System faster gripper change

SRH-plus

IP 67

Swivel Head

standard protection class

PGN-plus The No.

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2-Finger Parallel Gripper

with multi-tooth guidance

Your automated handling system.

It’s time to make use of your machine’s full potential. www.us.schunk.com/machine-potential Jens Lehmann, Brand Ambassador of SCHUNK, the family-owned company

Schunk 6-15.indd 89 AnzSynergie_PGNplus_SRH_SWS-I_US_0413_235x282-5.indd 1

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Hydraulic

HOSES

HYDRAULIC HOSE conveys hydraulic fluid to and among hydraulic components, valves, actuators and tools.

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hose is specifically designed to convey hydraulic fluid to or among hydraulic components, valves, actuators and tools. It is used in a variety of industrial applications. It is flexible and usually constructed with several layers of reinforcement because hydraulic systems frequently operate at high pressures. Dimensions, performance specifications, construction options and features are important parameters to consider when searching for hydraulic hose.

Important dimensions for the selection of hydraulic hose include the inside diameter, outside diameter and minimum bend radius. Hydraulic hose sizes are denoted by the inside and outside diameter of the hose. The inside diameter refers to the inside of the hose tube.

The outside diameter is often a nominal specification for hoses of corrugated or pleated construction. Minimum bend radius is based on a combination of acceptable hose cross-section deformation and mechanical bending limits of the reinforcement.

Construction options for hydraulic hose include reinforced, coiled, corrugated or convoluted.

Reinforced hose is constructed with some element of reinforcement—styles include spiral wire, textile braid, wire braid, wire helix and other designs in many plies or layer configurations. Coiled hose is designed for flexibility and elasticity. This feature often makes it expandable and easy to store. Corrugated hose contains corrugations, pleats or spiral convolutions to increase flexibility and capacity for compression and elongation. Multi-element hydraulic hoses are constructed of more than one hose formed or adhered together in a flat, ribbon or bundled configuration.

Additional features to consider include whether the hose requires integral end connections, anti-static, lay flat, crush-proof and flame-resistance characteristics.

In addition, material considerations include the type of fluid being conveyed and its concentration, as well as substances that may attack the hose cover.

Hose selection must ensure compatibility if it is to convey special oils or chemicals. The same holds for hose exposed to harsh environments. Substances such as UV light, ozone, saltwater, chemicals fluidpowerworld.com

6/18/15 7:28 PM

ISOBARIC HOSE MATCH YOUR HOSES TO YOUR SYSTEM PRESSURE STREAMLINE YOUR PRODUCTIONS STREAMLINE YOUR COSTS USE ISOBARICS Today’s equipment calls for the highest quality, robust and extremely flexible hoses. RYCO’s solution – our Isobaric hose range.

RYCO’s Isobaric hoses offer constant pressure performance throughout each range. This provides easy product selection and simplifies system design; a hose to suit all of your requirements.

The bright laylines help with product identification and selection.

KEEP YOUR EQUIPMENT PERFORMING AT ITS BEST

CONNECTING PARTNERSHIPS

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hoseassemblytips.com

7

EASY STEPS FOR SELECTING THE PROPER HOSE

An effective and easy way to remember hose

STAMPED

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selection criteria is to remember the word:

S = SIZE What is the inside diameter required?

Is the outside diameter a factor? How long does it need to be?

T = TEMPERATURE What is the temperature of the media?

What is the surrounding ambient temperature?

A = APPLICATION Where is this hose being used?

M = MATERIAL TO BE CONVEYED What is the media being transferred? Is the tube of the hose compatible?

P = PRESSURE What is the maximum system pressure? Is there any external force or pressure on the hose?

E = ENDS OR COUPLINGS What are the terminal end connections required to mate with the ports?

D = DELIVERY When are the hoses required? How many?

and pollutants can cause degradation and premature failure. For in-depth fluid compatibility data, consult the manufacturer.

While hydraulic hose is usually constructed of multiple materials, the most commonly used primary materials include elastomers, fluoropolymers and silicone, thermoplastics, metal, and composite or laminated structures.

Elastomeric or rubber hydraulic hose are often selected for their flexibility.

Fluoropolymer hose offer good flex life, superior chemical and corrosion resistance and can handle high temperatures. Thermoplastic hydraulic hose offer tight minimum bend radii and excellent kink resistance. Metal hoses can handle high temperature flow materials and often can handle higher pressures. They can be either stiff or flexible.

Flexible hoses are easier to route and install, compared with rigid tubing and pipe. They lessen vibration and noise, dampen pressure surges and permit movement between parts. In addition, increasing demands for higher productivity, efficiency and environmental compatibility are forcing hose manufacturers to improve product integrity—hoses now withstand higher pressures, extreme heat and cold and accommodate a range of fluids including today’s “green” variants.

Most hoses are manufactured to SAE J517 or European Norm (EN) Standards, the latter based on earlier DIN German standards. These standards predominate in the Americas, Europe and Australia. Both are also used throughout Asia, though that market is slowly gravitating toward EN specifications primarily because EN-rated hose has a higher pressure rating compared with similar-sized SAE hose. This gives greater safety factors should an application need the highest working pressure.

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Experience the precise power of DuraForce pumps and motors. Contact your Eaton sales representative today or visit eaton.com/DuraForce to learn more.

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Hydraulic

HOSE COUPLINGS IMPROPER

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selection or improper use of hoses, tubing, fittings and assemblies can cause failures, personal injury or property damage. Understanding the hose assembly and following the installation instructions provided by manufacturers will reduce these risks.

Engineers looking to specify hose couplings need to consider a few things besides correct size. Will the couplings be reused or permanent? Will they need a locking mechanism to prevent involuntary disconnection? Is one-handed operation required?

Couplings can be two types: permanent and field-attachable (reusable).

Permanent couplings are generally more reliable, easier and quicker to attach than field-attachable couplings, which makes them widely used in industry.

Crimping or swaging equipment (sometimes both) is needed to put a permanent coupling on a hose. Permanent couplings can be pre-assembled (one piece), with a ferrule permanently attached to the stem.

Higher-pressure hoses use field-attachable couplings, as well as permanent couplings. Fieldattachable couplings fit right on the hose using only a wrench and a vise. No special equipment is required. While handy, they do cost more than permanent couplings and take more time to attach.

There are three common types of coupling interfaces used in hydraulics today: thread interface, mated angle and O-ring.

Threaded couplings have two types of threads: male (outside threads) and female (inside threads). The National Pipe Tapered for Fuel (NPTF) has, as the name implies, a tapered thread. When the male and female components are threaded together, the tapered threads deform, applying pressure on one another, and thus making a tight seal.

Mated angle couplings form a seal when the male and female threads are screwed together. Two types of mated angle seals are SAE 45° and JIC 37°, but there are others. The NPSM seal is a mated angle.

Couplings with angle seats for sealing have straight or parallel threads. The threads themselves do not seal fluids as with tapered threads. Instead, the threads function to mechanically bring the two mating angle seats together.

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Kuriyama Hydraulics

HYDRAULIC HOSE, FITTINGS & ACCESSORIES

360 E. State Parkway, Schaumburg, IL 60173-5335

847-755-0360 | www.kuriyama.com | sales@kuriyama.com Kuriyama_FPH_6-15.indd 95

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HYDRAULIC HOSE COUPLINGS

National Pipe Straight Thread Mechanical Joint (NPSM) brings two 30° tapered seats together to make the seal. SAE 45° flare couplings are used on lower pressure applications, such as fuel lines, hot oil lines or refrigerant lines. JIC 37° angle seats are used on medium- and high-pressure lines on heavy equipment to join hydraulic hose assemblies to hydraulic system components.

There are three types of O-ring seal designs: O-ring boss, flat-face O-ring seal and O-ring flange. In the boss design, straight threads make the connection while a rubber O-ring makes the seal.

Threads pull the O-ring against the port, which has a machined groove for the O-ring, flattening it and making a seal that is excellent for high-pressure applications.

In a flat-face O-ring seal, the O-ring sits in a groove on the male’s face. The seal is made when the O-ring of the male meets the flat face of the female. The

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solid male O-ring face seal fitting will mate only with a swivel female O-ring face seal fitting.

O-ring flanges make high-pressure, large-diameter connections. A port is bored with a center outlet, surrounded by a smooth flat face, which has four tapped holes and four mounting bolts that tighten down onto flange clamps. There are no threads on this coupling. The flange itself has the groove for the O-ring.

There are several SAE and ISO standards that cover the performance requirements of hydraulic hose assemblies.

Included are the J517, J516 and J343 standards. The three most common ISO standards are ISO A, ISO B and ISO 16028.

The standard for performance testing is ISO 7241-2.

Hydraulic hoses that claim to meet SAE J517 standards (for example, SAE 100R1 and SAE 100R2) need to be designed for, and certified to, the criteria

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Patented design allows connection/disconnection under full working pressure.

Couplings and nipples available in both valved and valveless combinations. Compatible with working pressures to 290 PSI and temperatures up to 600ºF. Aerodynamic valve design offers superior flow capacity with minimal pressure drop.

Multi Connection Plate Systems CEJN custom built manifolds allow simultaneous connection and disconnection of an unlimited number of lines for a variety of media. Multiple combinations of nipples/ couplings sizes or materials available in stainless steel, brass, steel and anodized aluminum.

Customer.Service@cejnusa.com • 1-847-263-7200 • www.cejn.us

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defined by SAE. That criteria includes stringent dimensional tolerances (inside, outside and braid diameters), compound and reinforcement types, length changes, cold flexibility and ozone and heat resistance. There are also burst pressure and impulse requirements in J517. Those requirements are for coupled assemblies, and SAE states that “the general and dimensional standards for hydraulic hose fittings are obtained in SAE J526.”

Hydraulic hose fittings that meet SAE J516 standards are similarly well defined by SAE as to material type, dimensions, finish and so on. The SAE manual also specifically states that J516 fittings are intended to be used “in conjunction with hydraulic hoses specified in SAE J517 and used in hydraulic systems on mobile and stationary equipment.”

SAE J343 is the standard that establishes “uniform methods of the testing and performance evaluation of the SAE 100R series of hydraulic hose and hose assemblies.” Coupled assemblies are expected to meet or exceed SAE performance if the SAE criteria described above are met.

The integrity of any hose assembly depends upon the components, fittings and hose meeting the rigorous SAE requirements, and then the components being assembled by skilled personnel. This is true regardless of where the components are manufactured.

1. Hose size 2. Seat angle 3. Type of seat (inverted, flat) 4. Thread pitch 5. Maximum temperature 6. Maximum pressure 7. Hose material 8. Flow

FPW

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MANIFOLDS A HYDRAULIC

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manifold is a housing for surface and/or cartridge valves that regulate fluid flow between pumps, actuators and other components in a hydraulic system. It can be compared to a home’s electrical panel. Just as raw electrical power comes to the panel and is distributed to various household circuits to do work (provide light, power the dishwasher, operate the garage door), hydraulic oil under pressure is routed to the manifold by a pump where it is diverted to various circuits within the manifold to do work. The typical work performed by hydraulics is to rotate, clamp, press, extrude, lift, shear, extend and position.

For example, in the operation of a backhoe loader, the operator manipulates control valve levers, which, in turn, actuate valves mounted in or on a manifold. Connected to the manifold are various hoses that terminate where hydraulic power is transformed into mechanical action.

This transformation occurs when a hydraulic cylinder or motor responds to oil under pressure, and either extends, retracts, turns or brakes. Depending on which levers are being controlled, the operator can extend and swing the articulating arm backhoe loader or scoop gravel with the bucket, thus converting hydraulic power into work.

The role of a manifold is to bring the hydraulic circuits to life through the creation of a block machined in a manner consistent with the original circuit design. All valves have a series of orifices to which drilled holes in the manifold must communicate.

The configuration of these drilled holes in the manifold is the representation of the defined circuit.

The manifold is the central muscle control of the hydraulic system receiving inputs from switches, manual operations (levers) or electronic feedback systems. These inputs energize various valves mounted on or in the manifold, while specific oil pathways allow oil to flow through hydraulic lines to the appropriate actuator to perform work. The complex matrix of variables can make manifold design and component selection a challenging and rewarding art form, as size, weight, function, performance and operating environment are always part of the design consideration.

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HYDRAULIC MANIFOLDS offer a variety of paths for fluid to flow through a hydraulic system.

These acrylic models demonstrate complexities in their design.

In addition to providing a neat and logical layout, consolidating components into a manifold reduces space and pressure drop.

This results in fewer fittings, more efficient assembly times and reduced leak points. Manifolds are sometimes viewed as black boxes, as they can be highly complex with upward of 500 holes communicating with each other and many valves on a single block.

The alternative to manifolding a system is to mount all valving in individual blocks and plumb hoses in a manner consistent with the circuit. This dramatically increases the visual nature of the system, introduces infinitely more leak points and is generally an unacceptable alternative to manifolds. If a system is properly designed and test points provided in key locations, finding a problem becomes much quicker and simpler with a manifolded system. If transducers and other data collection devices are connected to these test points, the data may be linked into the machine controller and operation’s terminal displays.

Manifolds generally operate within 500 to 6,000 psi operating pressures. With additional design considerations, 10,000 psi can be achieved within the scope of steel and stainless-steel manifold designs. Although not typical in hydraulic application, 50,000 psi can be achieved with special materials and design nuances.

Manifolds come in three basic types. Most common is a solid-block design that contains all drilled passages and valves for an entire system. Typical materials for solid-block manifolds are aluminum, steel and ductile iron. Block weight can reach 100,000 lb.

Modular-block, or stackable design, is a subset of the drilled block. Each modular block usually supports only one or two valves and contains interconnecting passages for these valves as well as flow-through provisions. It normally is connected to a series of similar modular blocks to make up a system. This system is known for its flexibility within a limited range of circuit complexity. Modular block designs are generally held together FLUID POWER WORLD

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CONSIDERATIONS WHEN SELECTING A HYDRAULIC MANIFOLD • Fluid type • Seal materials • Material and finish • Environmental conditions and temperatures • Pressure (maximum and working) • Duty cycle • Flow conditions (pump, accumulator and return) • Port sizes, types and locations • Number and type of valves • Electrical voltage and connection • Mounting

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HANDBOOK

with tie rods or a system of tapped holes that allows for machine screw connections.

Lastly, laminar manifolds complete the manifold category. Laminar manifolds are usually made of steel, with passages milled or machined through several plates of metal.

These plates are stacked or sandwiched with the various fluid paths determined by the shape of the machined passages.

Solid-metal end pieces are added, and the whole stack is brazed together. Internal passages can be cut to any shape needed, so nearly any flow rate can be accommodated with minimal pressure drop.

Laminar manifolds are always custom-designed. Valves and other connections can be located where appropriate for a specific application. But because of the permanently shaped flow passages and brazed construction, this type of manifold cannot be modified easily if future circuit changes become necessary.

Because there are so many configurations available for manifold design, there are several software packages available to help the engineer design a system. With advances of these design software packages and CNC technology, the installed cost for custom solid-block manifolds, even small runs, is highly competitive to systems using modular blocks or discrete components.

FP

HYDRAULIC MANIFOLDS

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Hydraulic

MOTORS

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HYDRAULIC

THREE COMMON DESIGNS

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Keep in mind that the three different types of motors have different characteristics. Gear motors work best at medium pressures and flows, and are usually the lowest cost. Vane motors, on the other hand, offer medium pressure ratings and high flows, with a mid-range cost. At the most expensive, piston motors offer the highest flow, pressure and efficiency ratings.

GEAR MOTORS Gear motors feature two gears, one being the driven gear—which is attached to the output shaft—and the idler gear. Their function is simple: high-pressure oil is ported into one side of the gears, where it flows around the gears and housing, to the outlet port and compressed out of the motor. Meshing of the gears is a bi-product of high-pressure inlet flow acting on the gear teeth. What actually prevents fluid from leaking from the low pressure (outlet) side to the high pressure (inlet) side is the pressure differential. With gear motors, you must be concerned with leakage from the inlet to outlet, which reduces motor efficiency and creates heat as well.

In addition to their low cost, gear motors do not fail as quickly or as easily as other styles, because the gears wear down the housing and bushings before a catastrophic failure can occur.

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motors are rotary actuators that convert hydraulic (fluid) energy into mechanical power. They work in tandem with a hydraulic pump, which converts mechanical power into fluid (hydraulic) power. Hydraulic motors provide the force and supply the motion to move an external load.

Three common types of hydraulic motors are used most often today—gear, vane and piston—with a variety of styles available among them. In addition, several other varieties exist that are less commonly used, including gerotor or gerolor (orbital or roller star) motors.

Hydraulic motors can be either fixed- or variable-displacement and operate either bi-directionally or uni-directionally. Fixeddisplacement motors drive a load at a constant speed while a constant input flow is provided.

Variable-displacement motors can offer varying flow rates by changing the displacement. Fixeddisplacement motors provide constant torque; variable-displacement designs provide variable torque and speed.

Torque, or the turning and twisting effort of the force of the motor, is expressed in in.-lb or ft-lb (Nm). Three different types of torque exist.

First is breakaway torque, which is normally used to define the minimum torque required to start a motor with no load. This torque is based on the internal friction in the motor and describes the initial “breakaway” torque required EXTERNAL GEAR MOTOR. to start the motor. Next is running torque, which produces enough torque to keep the load running. Last is starting torque, which is the minimum torque required to start a motor under load and is a combination of energy required to overcome the force of the load and internal motor friction. The ratio of actual torque to theoretical torque gives you fluidpowerworld.com

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VANE MOTORS

HANDBOOK

At the medium-pressure and cost range, vane motors feature a housing with an eccentric bore.

Vane rotors slide in and out, run by the eccentric bore. The movement of the pressurized fluid causes an unbalanced force, which in turn forces the rotor to turn in one direction.

PISTON-TYPE MOTORS

FP

are available in a variety of different styles, including radial, axial and other less common designs.

Radial-piston motors feature pistons arranged perpendicularly to the crankshaft’s axis. As the crankshaft rotates, the pistons are moved linearly by the fluid pressure. Axial-piston designs feature a number of pistons arranged in a circular pattern inside a housing (cylinder block, rotor or barrel).

This housing rotates about its axis by a shaft that is aligned with the pumping pistons.

RADIAL PISTON MOTOR. Two designs of axial piston motors exist—swashplate and bent axis types. Swashplate designs feature the pistons and drive shaft in a parallel arrangement. In the bent axis version, the pistons are arranged at an angle to the main drive shaft.

Of the lesser used two designs, roller star motors offer lower friction, higher mechanical efficiency and higher start-up torque than gerotor designs. In addition, they provide smooth, low-speed operation and offer longer life with less wear on the rollers. Gerotors provide continuous fluid-tight sealing throughout their smooth operation.

the mechanical efficiency of a hydraulic motor.

Defining a hydraulic motor’s internal volume is done simply by looking at its displacement, thus the oil volume that is introduced into the motor during one output shaft revolution, in either in.3/ VANE MOTOR. rev or cc/rev, is the motor’s volume. This can be calculated by adding the volumes of the motor chambers or by rotating the motor’s shaft one turn and collecting the oil manually, then measuring it.

Flow rate is the oil volume that is introduced into the motor per unit of time for a constant output speed, in gallons per minute (gpm) or liter per minute (lpm). This can be calculated by multiplying the motor displacement with the running speed, or simply by gauging with a flowmeter. You can also manually measure by rotating the motor’s shaft one turn and collecting the fluid manually.

FPW

DUAL-DISPLACEMENT MOTOR, with swashplate design.

SPECIFYING HYDRAULIC MOTORS There are several important things to consider when selecting a hydraulic motor. You must know the maximum operating pressure, speed and torque the motor will need to accommodate. Knowing its displacement and flow requirements within a system is equally important.

Hydraulic motors can use different types of fluids, so you must know the system’s requirements—does it need a bio-based, environmentally-friendly fluid or fire-resistant one, for example. In addition, contamination can be a FIXED, AXIAL PISTON MOTOR, with the bent-axis design.

problem, so knowing its resistance levels is important.

Cost is clearly a huge factor in any component selection, but initial cost and expected life are just one part of this.

You must also know the motor’s efficiency rating, as this will factor in whether it runs cost-effectively or not. In addition, a component that is easy to repair and maintain or is easily changed out with other brands will reduce overall system costs in the end. Finally, consider the motor’s

VARIABLE, AXIAL PISTON MOTOR, with the bent-axis design.

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size and weight, as this will impact the size and weight of the system or machine with which it is being used.

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FP

HANDBOOK

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Pressure

TRANSDUCERS PRESSURE

is defined as the force per given area required to stop a fluid expanding.

Pressure transducers, which are a subset of pressure sensors, can be any number of devices that sample and record the pressure in a system. A pressure transducer converts a pressure measurement into an analog electrical output signal, which can be used by sensing instrumentation such as microprocessors and computers. Most often, this is accomplished simply, through physical deformation or mechanical deflection.

Important criteria to consider when selecting a pressure transducer are the general mechanism type, input and output, and performance specifications.

The most common types of pressure transducers are strain gauge, and thick/thin film. Strain gauge transducers use the mechanical deformation under pressure of strain-sensitive variable resistors, which may be integrated into measurement circuits such

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as a wheatstone bridge. In a thick/thin film transducer, a titanium nitride or polysilicon film may be applied to sensing equipment to impart the circuit with piezoelectric sensitivity to pressure.

Almost all pressure transducers require a source of electrical input. The transducer input voltage can vary but typically falls under 10 V, while the output is typically in the hundreds of thousandths of volts. A change in the system’s pressure would cause a change in the transducer’s resistance on the electrical circuit and would result in a change to the output voltage. With the aid of an analog to digital converter (ADC), the transducer’s output signal can be used in systems that require digital signals.

For example, a programmable logic controller (PLC) or a programmable automation controller (PAC) can use the digital signal to monitor the pressure and take action if needed.

Some pressure transducers output current rather than voltage, and are then often referred to as transmitters. These values fluidpowerworld.com

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PRESSURE TRANSDUCERS

HANDBOOK FP

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TIPS ON SPECIFYING PRESSURE TRANSDUCERS • Pick a robust pressure transducer. Hydrau-

• Consider potential pressure spikes. A rap-

• Remember location. Mount the pres-

lic applications can be remarkably difficult

id pressure increase that greatly exceeds

sure sensor close to the main line,

for pressure sensors. A proper transducer

normal working pressure is a pressure

actuator or volume of interest, but keep

design must survive mechanical stress at

spike. Severe pressure spikes can exceed

location serviceable. If you think the

the installation point and hydraulic pres-

working pressure, offset calibration and

sensor is exposed to severe mechani-

sure spikes.

damage electronics inside the device.

cal shock, high vibration or physical

Think of a pendulum swinging, where the

damage, move it. Add a short length of

raised ball represents this pressure peak.

hose and find a more stable location.

time and replacements can dwarf the

It is about to strike your thin metal disc,

Minimize the risk of early transducer

original purchase cost. If the data sheet

which has a circuit device glued to the

failure by selecting the right device and

states nothing about mechanical shock

opposite side. Some of the worst pressure

putting it in the correct location.

and vibration testing, ask for details or

spikes occur in manual operation during a

keep looking.

system startup.

• Think total cost. Troubleshooting, down-

typically fall within tens of thousandths of amps. When choosing the output of a pressure transducer, it is important to keep in mind the input requirements of the device that will be accepting the signal, the distance the signal must travel, and possible interference that can be found in the environment around the system.

Important performance criteria to consider are the pressure transducer’s operating pressure range, maximum rated pressure, accuracy and operating temperature range. The operating pressure range demarcates the intended pressure bounds at which the transducer has been designed to perform optimally.

The maximum rated pressure is the highest allowable pressure that the pressure transducer is rated to withstand.

The accuracy of the transducer is usually represented by suppliers in terms of ASME B40.1 grades: 4A (0.1%), 3A (0.25%), 2A (0.5%), A (1%), B (2%), C (3%) and D (4%) deviance from the true pressure value. A good pressure transducer is designed to operate independently of temperature; however, the operating temperature specifies a “safe” range, outside of which temperature may significantly affect the accuracy of pressure sensing.

For typical industrial applications, select a 0.5% accuracy class. This should be sufficient for most closed-loop systems.

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TIPS ON SPECIFYING PRESSURE TRANSDUCERS • Keep it short. Avoid using test or measurement hose

the remaining air becomes entrained in the hy-

longer than 1 or 2 ft, unless you only plan to measure

draulic fluid, where it eventually escapes in the

static pressures. Never use long measurement hose if

tank. (Entrained air … it sounds rather pleasant,

the transducer provides feedback to an active closed-

except for the violent implosion that occurs as

loop system, as it slows pressure feedback, which can

these air pockets collapse at high pressures. This is

make your PID system unstable.

another kind of pressure spike that you might wish to avoid inside your pressure sensor. )

ways. This prevents trapped air inside the transducer,

• Avoid using transducers with built-in orifices. Or add a

which causes a delay in reading the actual hydraulic

gauge snubber. These are used to improve transducer

pressure. If you commission a system with maximum

life or to hide poor pressure regulation. However, add-

pressure of 1,400 psi or lower pressure, you must manu-

ing a hydraulic delay leads to pressure instability in a

ally bleed air from all high points. Above this pressure,

closed-loop control system.

Higher accuracy will quickly increase price. Before making that investment, determine if the rest of your system requires this higher accuracy.

Accuracy is a constant value found on the data sheet. Unfortunately, most hydraulic systems start cold and get hot, so your actual pressure accuracy will depend on temperature change, too. The overall accuracy is accuracy class plus error due to temperature change.

EXAMPLE

HANDBOOK

• If possible, install the hydraulic port facing up or side-

FP

PRESSURE TRANSDUCERS

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Consider two transducers, identical except different temperature ratings.

First one is 0.2%/10° K; second one is 0.2%/10° K. Your hydraulic system changes from 20° to 50° C. Both transducers are 0.5% accuracy class.

#1 Overall accuracy (0.5% + 0.6% ) or 1.1% #2 Overall accuracy (0.5% + 0.3% ) or 0.8%

The most common output for industrial transducers is 0 to 10 Vdc. Gaining popularity is 0.1 to 10 Vdc, because the control system can detect a transducer fault. If the pressure signal falls below 0.1 Vdc, either the cable has been disconnected or the transducer has failed.

For longer cable runs, a 4 to 20 mA output is preferable. Pressure transmitters reject electrical noise, so the analog signal is clean. The 4 mA offset helps the control system detect sensor faults. However, 4 to 20 mA transmitters have 20% lower resolution, because the 0 to 4 mA is not usable.

FPW

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HANDBOOK

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PTOs &

GEARBOXES PTOs —

PTO. The crankshaft-driven method of power transmission is often used for hydraulic pumps mounted to the front of an on-highway truck, such as a plow/spreader or cement mixer. In this drive configuration, a small shaft with U-joints attaches to a yoke coupler to turn the pump.

The tractor PTO goes back pretty much as far as tractors do. Most early PTOs were driven from the transmission, which was located at the back of the tractor, to allow for easy location of an output shaft. The transmission type of PTO is only engaged when the transmission clutch is also engaged, and is coupled directly to transmission, so that when

The Power Take-Off, most commonly referred to by its acronym, PTO, is a common form of mechanical power delivery in the mobile machine market. The PTO is a method of transferring high power and torque from the engine (usually through the transmission) of trucks and tractors. In combination with gearboxes and pump mounts, nearly any type of mechanical power transmission is possible.

There are three common power take-off methods in the mobile machine market: tractor style, truck transmission style and engine crankshaft-driven, although the latter is not commonly referred to as a

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the clutch is depressed, the PTO isn’t driven.

If the transmission is driving the wheels, then the transmission PTO is turning. This also means the implement can backward-power the transmission as well as when the clutch is depressed, such as down a hill or if the attachment has a mechanism with high rotational inertia, resulting in surging of the drive wheels. This can be avoided by adding a dedicated overrunning clutch for the PTO, which prevents torque from being applied in the opposite direction.

A live PTO often uses a transmission clutch with two stages.

The first stage of the clutch operates the driven portion of the transmission, fluidpowerworld.com

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PTOs & GEARBOXES

HANDBOOK FP

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and the second stage of the clutch controls the engagement of the PTO. This method allows independent control of the transmission, so that the PTO maintains operation regardless of transmission clutch activity, including stopping of the tractor itself. For a tractor with a mower attachment, for example, this is a minimum requirement; you can’t have the mower turn off when you feather the clutch up a hill and around a tree.

The independent PTO has an entirely separate engagement clutch and works altogether exclusively of the transmission clutch. To engage the PTO, a button or lever is pushed; it’s that simple. Usually, a lever operated clutch is required to be activated before a separate PTO switch. Not only is the system easy, the independent PTO can be activated while the tractor is stopped or moving.

Independent PTOs are available in both mechanical and hydrostatic configurations, and as you can imagine, the hydraulic type is highly popular with the proliferation of hydrostatic drives.

The PTO shaft extending from back of the tractor is a male-splined structure. There are three types of PTO shafts, and their usage is loosely defined by the power output of the tractor. Each of the shafts runs at one of two standard speeds: 540 and 1,000 rpm. Also, each of the shafts comes in one of two diameters; 13⁄8 or 13⁄4 inches. Finally, none of the three shafts share a number of splines: 540 rpm—6 spline—13⁄8-in. shaft 1,000 rpm—21 spline—13⁄8-in. shaft 1,000 rpm—20 spline—13⁄4-in. shaft

The two 1,000-rpm shafts are known as the small (13⁄8-in.) and large (13⁄4-in.) versions. Each shaft is designed for an appropriate range of torque and horsepower transmission, and the differing dimensions ensure they are not used interchangeably. Some tractors can operate more than one speed and power range of shafts, but it is important to remember that the implements they drive are often limited to a design speed. So if a grain auger is designed to run at 540 rpm, it might not be a good idea to try to crank it up to 1,000 rpm.

Safety is serious business with PTO shafts, because unfortunately, they are infamous for causing both injury and death. Implements should only be operated with the PTO safety covers in place, and if there is a reason they don’t exist, extra caution needs to be practiced.

All modern heavy-duty trucks come with the capability to run a PTO from the transmission. The truck’s transmission will have a cover plate (or two), which can be removed, exposing a spur gear able to drive a PTO. The truckmounted PTO is versatile, although unlike tractor PTOs, they are not quite as universal—mostly because of the countless transmissions on the market.

Regardless, few transmissions have no PTO available.

The simplest form of PTO is with a single gear to mesh with the transmission’s output gear. These types are somewhat restricted in both their speed and horsepower range, but are more economical due to their simplicity.

PTOs with two or three gears are more common, and are also available for heavy-duty applications requiring high horsepower, torque and speed. Multiple gears allow for a wider range of speed or torque multiplication.

SELECTING A PTO

114

When selecting a PTO, you will need to pro-

You will also need to know what pad mount is

Even with the high torque that can be trans-

vide your supplier with various parameters,

necessary for the pump you’re running off the

mitted by PTOs, there are occasions when

as these units are not universal. You will need

PTO, such as SAE 2- or 4-bolt flange, and the

even more torque is demanded than a tractor

to know your transmission model number,

series, such as SAE B or SAE C 4-bolt flange.

can transmit (or slower speed than a standard

output speed, torque and horsepower

Special consideration should be paid when

540 or 1,000 rpm PTO). Although implements

required and the shifter style desired. The

mounting a pump to the PTO, as port loca-

often employ pulleys and chain drives, which

shifter engages and disengages the PTO, and

tion could interfere with chassis components

can be used for torque multiplication, the

is available with air shift, electric shift and me-

or the transmission itself. These issues are

heaviest of demands require a gearbox for

chanical (cable) shift. Some newer PTOs are

often resolved by installing an intermediate

reliable and efficient operation. Using gear-

operated by a clutch instead of sliding gears,

shaft, allowing the pump to be mounted

boxes is not limited to farm applications. They

but the application information changes little

in a clear location a couple feet behind the

are most often seen in wheel drives and other

otherwise.

transmission.

massive-torque, low-speed applications.

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GEARBOXES —

FPW

HANDBOOK

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Gearboxes are applied to either increase torque or increase speed, and it should be clear that increasing one decreases the other. When used to increase torque, they can achieve this at ratios anywhere from 2:1 relative to input torque, to 10,000:1 or more … which of course would slow the output speed drastically. When used to increase speed, sometimes planetary or helical/spur gearboxes can be used in reverse. A common use for overdriven gearboxes is for pump drives. A 1,000-rpm PTO speed doesn’t take advantage of a hydraulic pump capable of 3,000 rpm, so a speed-increasing gearbox/pump mount would allow for the use of a smaller pump.

Please note, worm gear reducers do not allow input energy at their output shaft.

FP

There are a few general types of gearboxes, including planetary, spur/helical gear and worm gear. Each has advantages and applications for which they are best suited. The most common type for mobile and off-highway machinery is the planetary drive. These consist of a center “sun” gear with three or more circumferential “planet” gears, which in turn are surrounded by a ring gear. Planetary gearboxes are robust and capable of holding high radial loads, especially when the load is correctly centered. This is why they’re often found in wheel drive applications.

Spur- or helical-gear style gearboxes use two or more gears meshed side by side, and are often used in industrial applications, such as a rolling mill. Their size and possible gear ratios vary widely, with the upper end of torque capacity only limited by the size of gears able to be manufactured. These types of gearboxes can have input and output shafts on either the same or opposing sides.

Also quite popular are worm gear style gearboxes. They employ a helical axial input shaft, which directs force across a perpendicular gear ring that is attached to the output shaft.

Operation is always with input and output 90° from each other. Worm gear units are generally light to medium duty.

PTOs & GEARBOXES

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Hydraulic

PUMPS POSITIVE HANDBOOK

displacement pumps are used in fluid power motion control applications. They have a small clearance between rotating and stationary parts. These pumps deliver a specific amount of fluid to the system for each revolution.

Positive-displacement pumps can be further divided into two categories: fixed- and variable-displacement. Fixed-displacement pumps provide a single, specific volume displacement per revolution.

In variable-displacement pumps, displacement per cycle can vary from zero to maximum volumetric capacity. Some of the more widely used types of positive-displacement pumps are gear, piston and vane.

FP 

GEAR PUMPS can be either internal or external styles. External gear pumps are one of the most popular types used in modern hydraulic systems. Gear pumps produce flow by using the teeth of two meshing gears to move the fluid. Their simple construction ensures limited purchase costs and servicing. They feature decent mechanical and volumetric efficiency, compact dimensions and low weight/ power ratio. Of the three common types of positive displacement pumps, gear pumps are the least efficient; their appeal is low cost and simple design.

EXTERNAL GEAR PUMPS can be equipped with straight spur (the most common type), helical or herringbone gears. In operation, the drive gear and driven gear rotate, creating a partial vacuum at the pump inlet (where gear teeth unmesh) that draws fluid into gear teeth. Gear teeth mesh at the outlet, forcing fluid out of the pump.

INTERNAL GEAR PUMPS contain one internal and one external gear. They pump fluid in the same manner as external spur gear pumps. In the basic design, the internal gear, which drives the outer gear, has one tooth less than the outer gear. As they mesh, the teeth create sliding seal points. Because their transition zone from low to high pressure (the area over the crescent) is relatively long, internal gear pumps can offer lower noise levels than some other types of pumps.

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Slim Dimensions Solid Performance

The V60N high pressure pump with 130 ccm.

HAWE‘s V60N-130 variable displacement axial piston pump has working pressures up to 5800 psi and displacement volumes up to 8 in3/rev., making it ideal for high pressures and high volumes. This pump has a high self-priming speed rating and a quiet operating noise level. Weighing only 68 lbs, it is one of the most power dense products on the market. Discover our comprehensive product range of axial piston pumps for industrial and mobile applications at www.haweusa.com.

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HYDRAULIC PUMPS

CONSIDERATIONS WHEN SELECTING A HYDRAULIC PUMP 1. Displacement 2. Pressure 3. Angle 4. Related torque 5. Weight 6. Mounting configuration

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GEARS are made of special steel and are often case hardened and quench hardened. Then gears are ground and fine finished. Proper tooth profile design and geometric proportions can reduce pulsation and noise levels during pump operation.

PISTON PUMPS supply high flows at high speed.

Two types of piston pumps—axial and radial—are manufactured in both fixed- and variable-displacement versions. Axial-piston pumps contain one or more pistons that convert rotary shaft motion into axial reciprocating motion. An angled cam (or wobble plate) rotates, causing pistons to reciprocate and take fluid in as they move toward the thin part of the plate. Fluid is expelled as pistons approach the thick end. In the bent-axis design, both pistons and shaft rotate, making a wobble plate unnecessary. Bent-axis pumps use the drive shaft to rotate pistons.

New Customers special pricing. Contact SKI for more details.

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Reduce energy costs by up to 80%

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Rexroth 4EE for energy efficiency helps lower energy consumption in your fluid power systems, reducing operating costs and strengthening your competitive edge. Our innovative Sytronix variablespeed pumps combine advanced digital controls with reliable, powerful hydraulics to help reduce energy costs by up to 80% and lower noise emissions by as much as 20 dB(A). Our systemic approach offers comprehensive energy reduction solutions across your entire operation: Technologies such as optimized hydraulic pumps for mobile machines, low-friction chain conveyors and regenerative electric drives give you a comprehensive array of components and systems with energy-reduction features already engineered in. Get exactly the results you need. Only from Rexroth.

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HYDRAULIC PUMPS

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With the longer sealing paths along the piston walls, piston pump efficiencies tend to be higher than other types of pumps. In addition, variable-displacement pumps can provide savings by only providing the pumping necessary for the function, saving additional energy and costs.

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RADIAL-PISTON PUMPS (fixed-displacement) are used especially for high pressure and relatively small flows.

Pressures of up to 10,000 psi are common. Variabledisplacement is not possible, but sometimes the pump is designed in such a way that the plungers can be switched off one by one, so that a sort of variable-displacement pump is obtained.

Radial-piston pumps are characterized by a radial piston arrangement within a cylinder block. As pistons reciprocate, they convert rotary shaft motion into radial motion. One version has cylindrical pistons, while another uses ball-shaped pistons. Another classification refers to porting: Check-valve radial-piston pumps use a rotating cam to reciprocate pistons; pintle-valve pumps have a rotating cylinder block, and piston heads contact an eccentric stationary reaction ring.

ROTARY VANE PUMPS (fixed and simple adjustable displacement) generally have higher efficiencies and lower noise levels than gear pumps. They can be used for mid pressures of 2,500 psi.

Some types of vane pumps can change the center of the vane body, so that a simple adjustable pump is obtained. These adjustable vane pumps are constant pressure or constant power pumps. Displacement is increased until the required pressure or power is reached and subsequently the displacement or swept volume is decreased until equilibrium is reached.

A critical element in vane pump design is how the vanes are pushed into contact with the pump housing, and how the vane tips are machined at this very point.

Several types of “lip” designs are used, and the main objective is to provide a tight seal between the inside of the housing and the vane, and at the same time to minimize wear and metal-to-metal contact. Forcing the vane out of the rotating center and toward the pump housing is accomplished using spring-loaded vanes, or more traditionally, vanes loaded hydrodynamically (by the pressurized system fluid).

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C E L E B R A T I N G

PERMCO IS A LEADING MANUFACTURER OF HIGH-PRESSURE HYDRAULIC GEAR / VANE PUMPS AND MOTORS, FLOW DIVIDERS, INTENSIFIERS, AND ACCESSORIES. AVAILABLE IN A WIDE VARIETY OF SIZES AND CONFIGURATIONS TO SUIT YOUR APPLICATION NEEDS. www.permco.com Global manufacturer of process control and factory automation solutions PERMCO, INC., 1500 Frost Road, P.O. Box 2068, Streetsboro, OH 44241 Toll Free: 800.626.2801 | Local: 330.626.2801 | Fax: 330.626.2805

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Replacement/

REBUILDS HYDRAULIC

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pumps, motors, cylinders and other elements in a system all function using the same fluid and interact with each other in complex ways. While each component is replaceable with an identical or aftermarket product, expertise, experience and specialized skill is required to correctly maintain and rebuild hydraulically powered equipment.

At all times, care must be taken to properly maintain the fluid cleanliness required by each component.

With digital sensors and electronic controls, hydraulic pumps and motors are increasingly sophisticated, more reliable and less failure-prone. However, when a base component fails, it needs a quick replacement to maintain operation and productivity. The field population of these advanced hydraulic components is increasing as the population of fluid powered machines and equipment grows.

Some hydraulic component manufacturers do not seem to take into account the potential opportunities to directly serve the end user. They are designed and structured to service the OEMs, leaving the end-user service and support to their distributors, repair shops or the service arms of equipment/machine manufacturers. This is an effective strategy, as long as the channel chain works together and replacement units and parts are widely and quickly available.

With the large size and geographic dispersion of the rebuild and repair market potential, the availability of replacement hydraulic components and parts is often less than the end user needs. Filling this void are the “form, fit and function” aftermarket hydraulic component and parts manufacturers, as well as a

AFTERMARKET AND REMANUFACTURED products often perform exactly as the original product did.

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large number of general hydraulic repair houses. These organizations are found in large cities and remote towns all across the globe. Some, but not all, of these aftermarket manufacturers and general repair houses are very skilled and effective. With care in selection, and by knowing the reputation of each organization, a user can be well served by this channel.

Aftermarket “equivalent” products often work exactly like the original product, and they provide a service to the industry, in keeping fluid-powered machinery and equipment up and running. Remanufactured original components also help fill the need for service or replacement of obsolete or hard-to-get components.

These repair services and aftermarket manufacturers are an integral part of the fluid power industry. Serviceoriented original component manufacturers and OEMs can and do work effectively to serve the user demand and market they create. Users’ needs for replacement units and parts are often sudden and unexpected. And usually, they need them fast. The manufacturers and channels of the fluid power industry must have easy-to-execute plans to serve the end users of hydraulic machines and equipment.

The planning for service and parts revenue should start at the product design stage. The life and mortality of the

product needs be taken into account at the production and inventory planning point. Important key planning activities are: • replacement aftermarket needs analysis • advanced production planning for limited production of older design products • coordination between component and OEM manufacturers • establishment of service centers located to meet market geographic requirements • continuous training of technicians at distributor service and repair operations • active relationship between independent repair houses and manufacturers These actions help generate better service, more machine and equipment reliability and meet the demands of the growing end user and replacement aftermarket.

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THOUSANDS OF REMANUFACTURING operations exist to rebuild pumps, motors, cylinders, valves, complete hydraulic power units and more. They also specialize in installing hose and other items to rebuild systems and make them function like new.

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Retaining

RINGS

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RETAINING

rings are engineered components used to hold many types of assemblies together. They are precision engineered to accurately position, locate and retain parts on shafts or in bores. The rings are installed into a groove, and all the other components of the assembly sit against and are retained by the ring. They help reduce costs by eliminating threading and other machining and offer reduced weights and sizes.

Retaining ring designs include spiral, tapered and constant section. Spiral rings do not have ears or lugs to interfere within the assembly like standard stamp rings. Tapered section rings feature compressible lugs to give them a circular shape in the groove, allowing them to grip tightly along the edge.

Constant section retaining rings are best suited for heavy-duty applications. They feature a uniform, constant section with no change in width throughout their entire circumference. Some specialty designs exist as well, including ones that feature a shallow groove for use on thin-walled sections of components.

In hydraulic systems, spiral retaining rings are used most often on the cylinder, particularly to retain the seal packing in cylinders. Retaining rings replace machined “steps” to retain the packing. Additionally, retaining rings are also found in hydraulic couplers, hydraulic pumps and other hydraulic components that need secure fastening. In pneumatic systems, they can be found in actuators, compressors, couplers and so on, to help fasten components as needed.

Standard materials for retaining rings include carbon steel, carbon spring steel, 302 stainless steel and 316 stainless steel.

Other available materials include phosphor bronze, beryllium copper, Inconel, Elgiloy and Hastelloy.

A different type of ring design, called a “scraper ring,” is also used in hydraulic cylinders. These rings help keep debris out of the seal portion of the cylinder to extend the life. They are typically made out of a soft material, such as beryllium copper, so they can hone to the shaft.

SPECIFYING RINGS FOR FLUID POWER SYSTEMS The most important detail to know when selecting a retaining ring for your application is to know if the groove for the ring will be located on a shaft (external) or in a bore (internal) and then specify the diameter of that shaft or bore. Additionally, if the ring will be subjected to axial thrust loads, the ring specifications need to be checked to determine whether a light-, medium- or heavy-duty ring is required. Finally, the material needs to be selected based on what type of corrosive media the ring will be subjected to.

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Hydraulic

ROTARY ACTUATORS

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rotary actuators are used for high torque, heavy-duty motion applications. They have high force capabilities, high power-per-unit weight and volume, good mechanical stiffness, and high dynamic response. They provide the heft for lifting, turning, indexing, clamping, mixing, bending, testing and steering applications among others.

Rotary actuators are compact and efficient, and produce high instantaneous torque in either direction. This makes them widely used in precision control systems and in heavy-duty machine tool, mobile, marine and aerospace applications.

Rotary actuators are coupled directly to a rotating load and provide good control for acceleration, operating speed, deceleration, smooth reversals and positioning. They allow flexibility in design and eliminate much of the bulk and weight of mechanical and electrical power transmissions.

Because they are fully enclosed, they withstand harsh conditions and are protected from dust, dirt and moisture.

ROTARY ACTUATOR STYLES The most common types of rotary actuators are vane, rackand-pinion and helical designs.

Vane actuators are a good fit for applications requiring extremely high endurance, high rotational speeds and a need for constant control of movement without the need to maintain the load in a particular position.

Their compact size makes vane actuators good for use in applications requiring positioning, harmonic motion and high-speed oscillating motion, and are used in tool machines, robotics and for handling containers.

In a single-vane actuator, the vane is rigidly attached to a central shaft in a cylindrical housing. The housing is divided into two chambers by a second vane or abutment shoe that is fixed to its internal diameter and extends to the output shaft. Hydraulic fluid flows to these chambers through connection ports closed to the fixed shoe. Pressure difference between the chambers acts on the moving vane area, producing torque directly FLUID POWER WORLD

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on the output shaft. Flow in and out of these chambers rotates the vane and shaft. Geometry usually limits the rotary movement of a single-vane actuator to 280°.

Double-vane actuators produce twice the torque and less than half the rotation of single-vane actuators. Two vanes and barriers provide a balance that counteracts the tendencies of unbalanced loads.

Mechanical efficiencies range from 80 to 95% and vane actuators transmit torques to nearly 700,000 lb-in.

Rack-and-pinion actuators are ideal for the highest demands on torque. They are ideal for applications where there is restricted building room in an axial direction; however, the rackand-pinion

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actuator requires considerably more space compared to the rotary vane and helical with equivalent torque output.

Rack-and-pinion actuators are particularly useful for heavyduty applications, and because of their constant torque output characteristics and resistance to drift, they are often used for precision control.

Rack-and-pinion actuators have low shock resistance, zero internal leakage and also have enclosed moving parts.

Helical actuators convert the linear motion of a piston into rotation by the use of helical gears that couple the piston to a rotating shaft. They feature high load capacity and are typically used to support the load as well as rotate it. This eliminates the need for other bearings or support mechanisms. Sometimes referred to as a “powered hinge,” the compact design of helical actuators makes them ideal when space constraints are a consideration. Their inherent load carrying ability allows simplification of many rotating load mechanism designs and, by eliminating other bearings and linkages, they offer the added benefit of increasing the reliability of the overall assembly.

Helical actuators produce the same torque in both clockwise and counterclockwise rotation.

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in theory, any rotation is possible.

Many actuators have 90, 180 and 360° rotations as standard, but models with custom rotation are also common.

Typical applications for helical actuators include aerial work platform and jib arm rotation, fork rotation, boom positioning, head rotation, valve operation, waste cart tippers, and wheel steering in the agriculture, construction, energy, marine, material handling, military and mining industries.

Other types of hydraulic rotary actuators include enclosed piston-crank, scotch-yoke and bladder designs. Enclosed piston-crank designs have adjustable stroke for variable shaft rotation up to 110°. A rod connected to a crank arm drives the rotating shaft. In scotchyoke actuators, two pistons are connected by a common rod. At the beginning and end of the stroke, torque output is twice the value produced at the stroke’s midpoint. Applications that require a high breaking torque to move the load find this type of actuator appropriate.

In bladder designs, a pair of rubber bladders are alternately pressurized and exhausted to produce the driving force. When pressurized, the bladder pushes against a cup-shaped lever arm that rotates the output shaft.

Zero internal leakage makes this actuator highly accurate and resistant to contamination.

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SELECTING A HYDRAULIC ROTARY ACTUATOR: • Duty (heavy, standard) • Rotation (90°,180°, 270°, 360°, custom) • Maximum output torque • Maximum holding torque • Acceptable backlash • Maximum bearing loads (moment, thrust, radial) • Hydraulic fluid • Hydraulic fluid operating temperatures • Mounting (flange, foot)

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KYB Americas Corporation 180 N. Meadow Rd. Addison, IL 60101 630.620.5555

The KYB MMP is an electric over hydraulic linear actuator specifically designed for mobile applications. The MMP is a compact, plug and play hydraulic system, completely sealed and IP67 weatherproofed for durability and quality built to provide a powerful solution for your mobile application.

www.kybfluidpower.com

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SEALS

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is a vital factor in the proper function of hydraulic applications, as leakage from the cylinder or across the piston, along with the ingress of unwanted contaminants, can decrease the lifespan and efficiency of the entire application.

There are numerous sealing products, technologies and techniques to both keep oil in and contaminants out of the hydraulic system, each providing unique benefits. Further, in some harsh applications, the features of individual seals do not fulfill the demanding requirements for the equipment and a sealing system is required.

MATERIAL OPTIONS Seal material choices are determined by the seal’s environment. For example, different types of chemicals react differently to different fluids, while some materials have higher pressure and temperature limits. They also must be able to withstand extrusion, so materials are very application-specific. Below is a listing of some of the most common sealing materials and their advantages for different applications and environments.

Polyurethane Polyurethane is an organic material of high molecular weight whose chemical composition is characterized by a large number of urethane groups. Urethanes belong to the thermoplastic elastomers (TPE) family and close the gap between thermoplastic and elastomeric materials regarding hardness, deforming behavior and consistency. Within certain temperature limits, polyurethane possesses the elastic characteristics of rubber combined with the advantages of a rigid plastic.

The composition of the material is determined by three components: polyol, diisocyanate and a chain extender. The type and amount of these materials used, and the reaction conditions, are decisive in determining the properties of the resulting polyurethane material. In general, polyurethanes possess the following properties: • high mechanical strength • high tensile strength • good abrasion resistance • hood flexibility • modulus of elasticity, which can be varied within wide limits • wide range of hardness values, while retaining good elasticity

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• good resistance to ozone and oxygen • outstanding resistance to abrasion and tear • good resistance to oil and gasoline Temperature range for use: -30 to 80° C; high performance types (compounds) up to 110° C in mineral oils (long-term exposure temperature).

Acrylonitrile-Butadiene-Rubber (NBR) NBR is a polymer of butadiene and acrylonitrile. The acrylonitrile (ACN) component affects the following properties of the NBR: • elasticity • cold flexibility • gas permeability • compression set • swelling resistance in mineral oils, greases and fuels

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SEAL DESIGNS Below is a list of some of the most common seal designs used in fluid power applications.

PISTON SEALS:

• provide aggressive wiping force to prevent mud, water, dirt and other contamination from entering the system • allow lubricating oil film to return to system on inward stroke

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• prevent system fluid from escaping to atmosphere • must provide sealing function at low and high pressure • require excellent extrusion and wear resistance • should provide good pump-back capability for lubricating oil film • often must withstand up to 6,000 psi

BUFFER SEALS: • must withstand high pressure exposure • protect the rod seal against pressure spikes • feature a pressure-relieving capability that prevents pressure build-up between seals

WEAR BANDS: • prevent contact between metal parts in the cylinder • center rod and piston from housing elements • increase seal life

O-RINGS: • most commonly used in static applications and radial or axial deformation to maintain sealing contact force • double-acting, so seal on both sides of a component • can be used as energizing elements or as primary seals • self-acting, so do not require additional system pressure or speed to create the seal

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WIPERS:

ROD SEALS:

• increase rod seal life • allow for wider extrusion gaps • require high wear resistance

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• provide sealing of the piston and barrel, critical to the function of the cylinder • most often a lip-seal design, but can also be O-rings, T-seals, and so on • must provide efficient sealing, but also reasonably low friction • made from various seal materials, depending on application • require system pressure to effectively activate the lip seal

• protect main sealing elements, thus increasing life of seals • often made from polyurethane, which offers high abrasion resistance • often used as a linkage pin grease seal

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An NBR material with low ACN content has very good cold flexibility (down to approximately -45° C) and moderate resistance to oil and fuel. In contrast, a material with very high ACN content with optimum resistance to oil and fuels, may have a cold temperature flexibility only down to -3° C. With rising ACN content, the elasticity and the gas permeability decrease and the compression set becomes worse.

NBR provides: • good resistance to swelling in aliphatic hydrocarbons; greases; fire retardant hydraulic fluids of Groups HFA, HFB and HFC; vegetable and animal oils and greases; light heating oil; and diesel fuel

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• good resistance to hot water at temperatures up to 100° C (sanitary fittings), inorganic acids and bases at concentrations, and temperatures which are not too high • moderate resistance to swelling in fuels having a high content of aromatics (super grades of fuel) • high swell in aromatic hydrocarbons, chlorinated hydrocarbons, flame retardant hydraulic fluids of the Group HFD, esters, polar solvents, and brake fluids based on glycol Temperature range for use (depending on the composition of the blend): -40 to 100° C and for short periods up to 130° C (the material hardens at higher temperatures).

For special blends, the cold flexibility extends down to -55° C.

Fluoro-Rubber (FKM) Copolymers, terpolymers or tetrapolymers with various compositions and with fluorine contents from 65 to 71%, which have varying resistance to surrounding media and varying cold flexibility, can be made by polymerization of vinylidne fluoride (VF) and variable amounts of hexafluoropropylene (HFP), tetrafluoroethylene (TFE), 1-hydropentafluoropropylene (HFPE) and perfluoro (methylvinylether) (FMVE). Crosslinking is achieved either with diamines and bisphenols or with organic peroxides.

FKM provides: • outstanding resistance to high heat • excellent resistance to oil, gasoline, hydraulic fluid and hydrocarbon solvents

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HYDRAULIC SEALS

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superior performance. High-pressure rod end sealing systems normally consist of four elements: the wiper, the rod seal (or main seal), the buffer seal (or secondary seal) and the wear (or guide) bands. The piston sealing system consists of

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a main seal combined with wear bands. The four most commonly used materials for hydraulic sealing applications are polyurethane (PU), acrylonitrilebutadiene-rubber (NBR), fluoro-rubber (FKM),

HANDBOOK

SPECIFYING SEALS:

Sealing systems use a combination of specific seals that work together to offer

and polytetrafluoroethylene (PTFE).

• good flame retardance • low permeability to gases • high swell in polar solvents and ketones, fire retardant hydraulic fluids of the Skydrol type and brake fluid Newly developed materials (cross-lined by peroxides) have good resistance to media, which can only be tolerated to a small extent, if at all, by conventional FKM. Temperature range for use: about -20 to 200° C (for short periods to 230° C). Special grades: -50° to 200° C.

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Polytetrafluoroethylene (PTFE) PTFE is a polymer of tetrafluoroethylene. This non-elastic material is characterized by: • slippery surface that repels most media • non-toxic at working temperatures up to 200° C • low coefficient of friction against most opposing surfaces made of other materials; stiction and friction are almost the same • excellent electrical insulating properties (almost independent of frequency, temperature and weathering effects) • chemical resistance that exceeds that of all other thermoplastics and elastomers • liquid alkali metals and a few fluorine compounds attack PTFE at higher temperatures The temperature tolerance is between -200° and 260° C; PTFE has some elasticity even at extremely low temperatures; therefore it is used in many extreme cold temperature applications. Most hydraulic applications require the use of a spring or elastomeric component to energize a lip seal configuration because of the low elasticity and tendency to cold flow over time.

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Hydraulic

VALVES HYDRAULIC HANDBOOK

valves, used in conjunction with the force density advantage of actuators, are what help make hydraulics unique in its control of force, torque and motion. Valves govern direction, pressure and flow of hydraulic fluid, enabling smooth, safe and controlled use of actuators.

Every machine both requires and uses valves, varying vastly in execution from a few valves to dozens on one machine. Their use can be as simple as a relief valve to protect your pump and actuator, such as the relief valve built into the kick-off valve on a logsplitter. Conversely, the complexity of a hydraulic circuit can be extensive, using a dozen valves per function as can be seen in manifolds, such as a pilot-operated valve with dual counterbalance valves, dual flow controls, and dual postcompensation and load sensing checks, all of which can be used in just a single cylinder circuit.

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DIRECTIONAL CONTROL VALVES The directional control valve is available in myriad configurations, and is named as such if its primary function is to somehow control the path of fluid flow. Directional control valves manage fluid by blocking, diverting, directing or dumping. Their complexity varies immensely (just like their cost), as does the method of integration. Valve construction runs the gamut from cartridge valves to monoblock valves, or subplate mounted valves to inline valves. Their usage depends on the industry in which they are typically applied.

The most basic directional valve is the check valve; it allows flow into one work port and blocks flow from coming back through the opposite work port. Alternatively, directional valves can be complex, such as with the pilot-operated valve.

A standard spool valve has one directly operated component that controls fluid through the valve. However, as flow increases, the force upon the spool also increases (especially as pressure increases as well), and these forces can prevent a spool from actuating, most often with electric coils. By using a small pilot valve to control the movement of the larger, main-stage spool, the size (and flow) of the valve are nearly limitless.

Directional valves are often described by the number of “ways” fluid can travel through them, and also by the positions available to be shifted into. The ways are equal to the number of work ports, so a 4-way valve will have Pressure, Tank and A&B work ports. Positions are equal to the number of positional envelopes. For example, one would describe a double-acting

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HYDRAULIC VALVES

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of itself rather than upstream. It is used in applications where sub-circuit pressures need to be lower, without sacrificing any performance in the rest of the system.

single monoblock valve as “4-way, 3-position,” or simply a “4/3 valve.”

Directional valves are available in monoblock or sectional valves, common to the mobile-hydraulic industry, as well as subplate mounted industrial type valves such as ISO style D03, D05 and so on. Also common to both mobile and industrial markets are cartridge valves installed into manifold blocks.

Cartridge valve manufacturers offer many unique products, and allow high levels of creativity with limitless available valve combinations.

FLOW CONTROL VALVES Flow control valves are any component designed to control or limit flow in one way or another. They are often just a needle valve, which is just a variable restriction, adjusted by a screw or knob much like pressure valves, to limit the energy potential to create flow. When installed with reverse flow check valves, we change the name to flow control.

Flow control valves can sometimes have multiple ports, such as with a priority flow control. They are able to provide controlled, fixed flow to one part of the circuit (sometimes at the sacrifice of another part) and as long as input flow is high enough for its priority demand.

Flow controls are ideally pressure compensated, which allows the valve to maintain its set flow regardless of loadinduced pressure variances. Pressure compensators are a type of flow control valve available as a single item, often added to other valves in a circuit to provide the same flow setting loadindependent accuracy, such as with a proportional valve, for example.

Proportional valves are considered both flow and directional valves, and are able to both meter flow and control the direction flow is metered in. Proportional valves use pulse-width modulation to maintain voltage and control current.

Varying the current controls the force of the magnetic field and how far the spool or poppet moves within its body, changing the size of the opening available for fluid to take, which of

PRESSURE CONTROLS A pressure valve is any component designed to limit pressure in some way.

Most pressure valves are based on a poppet being pushed against a seat with an adjustable spring, although pressure valves can be a simple ball and spring configuration or use spools for high flow circuits. Their operation is simple: a spring pushes the poppet against a seat, and when pressure from the system is strong enough to counteract the force of the spring, the valve will open, bleeding off fluid to limit pressure.

A relief valve controls maximum pressure for either the entire system or a sub-circuit of it, the lowest spring pressure of a system being the one to open up first. Most other pressure valves are based on the relief valve’s simple spring-loaded ball or poppet.

Sequence, counterbalance and brake valves are all forms of relief valves with added utility or functionality, such as reverse flow checks or pilot operation built in. The pressure-reducing valve differs from the other pressure valves because it limits pressure downstream FLUID POWER WORLD

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course limits flow. A simple variable resistor can be used to limit current, but it is inefficient and cannot provide the benefits a PWM controller can.

Firstly, a valve controller can provide adjustable minimum and maximum settings. A minimum current value is needed to move the spool past its overlap where it “starts” to flow.

Also, a maximum current value prevents too much electric juice from fatiguing the valve and coil when only a couple amps are required to achieve full flow anyway. Additionally, a proper controller and driver provide a dither signal to the valve, which vibrates the spool so that static friction doesn’t hold it up.

The spool movement is unnoticeable, but is enough so that when a change in current is required, the spool responds rapidly without overshooting the desired new position.

FPW

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