Fluid Power World February 2016

New twist on pneumatic muscles p.32

From the basic to advanced: selecting directional control valves p.38

Industrial variable speed drives p.48

February 2016

www.fluidpowerworld.com

More efficient

mobile hydraulic

troubleshooting PAGE 42

COVER_FPW 2-16.indd 1

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Get out and see some fluid power This year feels like an important one for trade shows—as I look at my calendar, it’s chock full of important events for the fluid power community. The staff of Fluid Power World will be at most of the following events, and it’s going to be hard to pick and choose which ones I’ll be able to attend myself.

Here’s a rundown of the shows we’ve identified as critical for 2016: March 1 – 4 ................................. Work Truck Show................................... Indianapolis March 3 – 5 ................................. Ag Connect Show.................................. New Orleans March 9 – 11 ............................... NFPA Annual Conference...................... San Antonio April 5 – 7 .................................... Reliable Plant Show............................... Louisville April 11 – 17 ................................ Bauma.................................................... Munich, Germany April 30 – May 4 .......................... NAHAD................................................... Colorado Springs May 2 – 5 ..................................... OTC Show.............................................. Houston May 16 – 19 ................................ AISTech.................................................. Pittsburgh June 22 – 23 ................................ Fluid Power Technology Conference..... Milwaukee August 15 – 17 ............................ NFPA’s IEOC........................................... Wheeling, Ill. September 26 – 28 ..................... MinExpo................................................. Las Vegas November 6 – 9 .......................... PackExpo................................................ Chicago November 30 – December 2....... International WorkBoat Show .............. New Orleans Which shows are you or your company planning to attend? Hopefully we’ll see you at some of these events—but if not, you can count on our staff to report on what’s happening at each one, as well as what the trends are and where the technology is headed. We’ll also have information on the newest products on our various websites, and we’re always busy on Twitter and social media, too. Follow our main account at @FluidPowerWorld or our individual editors at @DW_Editor, @DW_MaryGannon, @DW_MikeSantora and @wtwh_Michelle.

Next year will be an even bigger one, with the return of the triennial IFPE event in Las Vegas. We’re already planning our coverage of that event, scheduled for March 7 – 11, 2017. Stay tuned and see you on the road!

FPW

Paul J. Heney Editorial Director pheney@wtwhmedia.com

Available In BSPP

On Twitter @DW_Editor

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1-763-784-5531 www.SuperSwivels.com Editorial 2-16 FPW_Vs3 MD.MG.indd 2

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2 • 2016

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FEBRUARY 2016 • vol 3 no 1 • www.fluidpowerworld.com

excite your fingertips TOMPKINSIND.COM

EDITORIAL Editorial Director Paul J. Heney pheney@wtwhmedia.com @dw_editor

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Assistant Editor Michelle DiFrangia mdifrangia@wtwhmedia.com @wtwh_michelle

At tompkinsind.com we have the widest availability of hydraulic adapter configurations in the industry...all at your fingertips. In addition, you can download CAD drawings for over 6,000 adapters, use our custom search tool to cross-reference over 50,000 industry numbers, download bin labels for all of our hydraulic adapters and fittings, view online assembly videos, and more.

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Contributing Editor Josh Cosford @FluidPowerTips Contributing Editor Ken Korane kkorane@wtwhmedia.com @FPW_KenKorane

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vol 3 no 1

February 2016

C ontents |

|

fluidpowerworld.com

F E AT U R E S MEDICAL PNEUMATICS

New twist on pneumatic muscles Researchers are taking advantage of light, yet powerful pneumatics to improve life for pediatric patients.

HYDRAULIC VALVES

From the basic to advanced: selecting directional control valves

32 38

Directional control valves are fundamental components in any hydraulic system, but these workhorses have evolved from simple to sophisticated designs that lower system cost.

MOBILE HYDRAULICS

Mobile hydraulics troubleshooting Taking a methodical approach is the best way to get off-highway equipment working again, quickly and safely.

INDUSTRIAL HYDRAULICS

Hydraulic efficiency grows with variable speed drives

6

D E PA R T M E N T S

02 Editorial

42

08 Korane’s Outlook 30

10 Association Watch 14 Distributor Update 18 Energy Efficiency

48

20 Design Notes 22 Fundamentals

Combining hydraulic pumps with variable speed technology increases efficiency while reducing noise and environmental impacts.

FLUID POWER WORLD

Contents_FPW 2-16_Vs2 MG.indd 6

38

24 Training

56

28 Safety

30 Maintenance 56 Component Focus 58 Product World 60 Ad Index

ON THE COVER

Excavator valve manifolds greatly minimize hose connections while saving space. Illustration courtesy of CD Industrial Inc. 2 • 2016

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Ko ra n e ’s O u t L o o k Ken Korane • Contributing Editor

A simple path to higher efficiency Everyone is for energy efficiency—as long as it doesn’t cost too much. Replace an incandescent light with a new LED bulb?

Check. Find out an LED costs five times that of the old one? Maybe not so fast.

It’s no different with fluid-power systems. Engineers on a mission to improve efficiency can spend a lot of time comparing the benefits of high-efficiency pumps, VSDs and high-flow valves. But an oftenoverlooked way to make equipment more efficient is simply to change to a different hydraulic fluid.

Using the right fluid can noticeably improve overall machine efficiency and generate significant operating savings, according to Frank-Olaf Maehling, the global product manager for hydraulic fluids at Evonik Resource Efficiency in Darmstadt, Germany.

He explained a trend among OEMs is to downsize circuits by using smaller components while operating at higher pressures.

That increases power density, but it also puts greater demands on hydraulic systems and affects operating temperatures.

And that, in turn, affects fluid viscosity. It’s important to keep viscosity within a machine’s recommended limits (usually between 10 and 100 mm²/sec). However, basic monograde oils only maintain that viscosity within a limited temperature range.

A viscosity that’s too high or low hurts mechanical and volumetric efficiency.

To address that shortcoming, engineers at Evonik have developed a portfolio of temperature-sensitive polymer additives, termed Dynavis, that improve the viscosity index (VI) of standard hydraulic fluids.

Higher VI fluids maintain stable viscosity over a wider range of temperatures. These multigrade oils are thinner so components 8

FLUID POWER WORLD

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2 • 2016

experience less friction and quicker start-up when cold; and are thicker for better control and less leakage when hot. While VI improvers aren’t new, they’re increasingly important for higher energy efficiency in hydraulic equipment.

One might expect such benefits in outdoor settings with varied conditions, but engineers find equally compelling efficiency improvements indoors. That’s because all the different components in complex systems rarely run at exactly the same temperature.

Switching to energy-efficient hydraulic fluids often pays off handsomely. Field tests by Evonik in equipment like excavators, skid-steer loaders and injection-molding machines demonstrate efficiency increases as high as 30%, depending on the task. That directly equates to fuel or electricity savings that can run into the thousands of dollars per machine every year.

“A top-tier hydraulic fluid formulated with Dynavis technology is priced slightly higher than a monograde

hydraulic fluid,” Maehling admitted. “But significant savings are possible by spending a little bit more on fluid than just buying the cheapest available.”

Even considering the minor price premium, a growing number of equipment owners are recognizing the value of reliable operation and a lower total cost of ownership, he said. “Many classes of hydraulic equipment will benefit from a proper selection of the fluid.” Good candidates include construction; mining and agricultural equipment; marine onboard pumps and harbor cranes; and industrial presses, plastics processing machines, and pulp and paper manufacturing equipment.

FPW

Hyundai R220-LC excavator

www.fluidpowerworldonline.com

2/16/16 12:36 PM

O+P USA 10-15 FPW.indd 9

CRIMPING

CUTTING

FITTINGS ASSEMBLY

SKIVING

MARKING

WASHING

FILTERING

ACCESSORIES

TESTING MULTIFUNCTIONAL BENDING UNITS

PRE-ASSEMBLY

FLARING

DEBURRING

CRIMPING

CUTTING

FITTINGS ASSEMBLY

SKIVING

MARKING

WASHING

FILTERING

ACCESSORIES

TESTING MULTIFUNCTIONAL BENDING UNITS

PRE-ASSEMBLY

FLARING

DEBURRING

2/16/16 11:52 AM

ASSOCIATION WATCH

Paul Heney • Editorial Director

CCEFP, industry players brainstorm on human scale fluid power In December, 45 representatives from fluid power manufacturers, researchers, universities and industry associations met in Nashville at Vanderbilt University’s LASIR Laboratory to discuss the future of Human Scale Fluid Power.

Human Scale Fluid Power is, quite simply, about scale, and generally refers to applications under 10 kW. While industrial automation falls under this definition, this niche mostly focuses on human assist/therapeutic devices, medical devices, medical robots, exoskeletons, military robots and untethered devices.

Key technologies necessary for Human Scale Fluid Power are advanced pneumatics, miniature hydraulics and compact power.

A strategy for Human Scale Fluid Power for CCEFP was proposed and approved in October 2015, and this conference was seen as the next step in developing and pursuing goals for this technology. The Center also hopes, as a result of the event, to identify strategically aligned federal agencies that could be sources of funding.

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Co-chairs Prof. Eric Barth of Vanderbilt and Prof. Kim Stelson of the University of Minnesota gave overviews of the CCEFP’s history and funding issues moving forward, as well as the vision and strategy for Human Scale Fluid Power.

One new aspect to the CCEFP footprint is the development of “Centers of Excellence” at various universities. These include fluid power manufacturing at Georgia Tech, hydraulic components and systems research at Purdue, test and evaluation at MSOE, Powertrain research at Minnesota—and now pneumatics and Human Scale Fluid Power research at Vanderbilt.

Barth predicted that, “In 30 years, I think you’ll see some form of robot in every home in the U.S.” Between that opportunity and things such as wearable devices, he told the attendees that fluid power had a chance to be a driving force behind how the technology is designed and powered—as opposed to being merely a follower.

www.fluidpowerworld.com

2/17/16 12:10 PM

FluiDyne 2-16 FPW (NEW).indd 11

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ASSOCIATION WATCH

The attendees were split into three teams,

focusing on different issues: • MRI compatible, rehabilitation and human

assist devices • industrial pneumatics and factory

automation • mobile robots, exoskeletons and compact

fluid power components and supplies.

Attendees gave the Center some compelling ideas for application areas on where to focus

the funding search, including: • increasing patient transfer needs due to aging population can result in high rate of caregiver injury; there is a need for assistive devices operable in the home environment, and fluid power provides appropriate force

density and compactness

• material handling needs in industry; there is a high rate of injury (potentially

12

FLUID POWER WORLD

2 • 2016

similar to patient transfer needs, simpler on what makes an efficient system,

and lower risk relative to handling poorly applied systems are common,

humans) lack of awareness/education needed) • movement assistance devices for • productivity enhancements neuromuscular impaired population (collaborative robots, service robots would enhance societal health, even in places like a vineyard or productivity and quality of life agricultural field) (emerging market, currently with • safety (such as robots interacting closely electrically actuated devices, fluid with humans; noise, cleanliness, lost time power devices could improve capability, incidents represents a huge value but requires compact power supply) proposition/$50 billion in back injuries), • powered prosthetic limbs (there and is currently wide acceptance/use of • additional opportunities exist with hydraulic and pneumatic actuation in underwater robots, wearable lower limb prosthetics market, but exoskeletons, entertainment/sports, currently modulated passive; power is the battlefield, rescue/disaster. an opportunity but requires compact fluid power supply) CCEFP • energy efficiency/achieve more output ccefp.org with equal or less energy (misconception

UPDATED FPW 216 Dept Assoc Watch Vs3 MG.MD.indd 12

FPW

www.fluidpowerworld.com

3/27/2015 4:00 PM 2/16/16 3:46 PM

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DISTRIBUTOR UPDATE

Michelle DiFrangia • Assistant Editor

Learn, Share, Connect: NAHAD 2016 Meeting and Convention Pack your hiking shoes and ski vest (for that late-April snow), because NAHAD is headed to the mountains of Colorado Springs. The 32nd Annual NAHAD Meeting and Convention is being held April 30 – May 4 at The Broadmoor.

Learn, Share, Connect is the theme this year; fitting, as the convention can arguably be considered a four-day networking event.

With programs like the NAHAD Young Executives Luncheon, Speed Networking, and the Manufacturer and Associate Hospitality Suites, bringing a box (or two) of business cards might be the best decision you’ve made all week. In the convention brochure (distributed to members and past attendees earlier this year), NAHAD President Jim Reilly invites and encourages attendees to take advantage of all the convention has to offer. “Learn during our educational sessions and in conversations with your peers, share your company’s expertise with your suppliers and your customers, and connect in a meaningful way with all of the over 1,100 hose and fittings specialists that we expect to see,” he wrote.

While Reilly technically opens the event Saturday afternoon with his welcoming remarks, perhaps the true kick14

FLUID POWER WORLD

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2 • 2016

off is the Gala Dinner and George W. Carver Award and Presentation that evening. Amy Purdy, double-leg amputee, Paralympic bronze medalist in snowboarding, bestselling author, Dancing With the Stars alum, and co-founder of Adaptive Action Sports, will be the featured guest speaker.

By now it’s common knowledge that the downturn in the oil and gas industry will have drastic effects on fluid power as a whole in 2016. The big question on everyone’s mind is: How much of an effect will this new trend have on business, and what can be done to combat it? Tom Gale, president of MDM Analytics, and a panel of industry leaders address this concern during the Industry Leaders Panel: Critical Issues for the Hose Industry, where they will discuss “navigating rapidly shifting trends in natural resources, shifting workforce demographics, and the evolving global economic landscape.”

Make sure you have your Wheaties for breakfast Sunday morning, because school is back in session. The UID-in-a-day program offers six sessions—three concurrent meetings in the morning and three concurrent meetings in the afternoon— each of which focuses on a different facet of sales, from enhancing the bottom line

www.fluidpowerworld.com

2/17/16 12:51 PM

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DISTRIBUTOR UPDATE

to enriching relationships. Topics for 2016 include: Inside Sales 101; Value Added Selling; Know More! Relationships; and The Real Profit Drivers. Attendance can be used to earn credit toward a Certificate in Innovation Distribution from Purdue University.

Tuesday features the Showcase of Hose Solutions. Take a tour of the latest hose, fittings, equipment and services offered from the more than 150 manufacturing companies exhibiting at the showcase, and talk shop over the breakfast and lunch buffets provided to registered attendees.

Enjoy music, food and cocktails during the closing reception, when you have one last opportunity to network and make lasting business connections. And don’t forget to carve out some room for sight-

seeing or one of the many excursions offered to attendees and their guests, such as the Foothills Jeep Tour or Pikes Peak Cog Railway Tour.

Last year’s convention in Miami was my first, and as someone still new to the fluid power industry, it was an overwhelming yet eye-opening and amazing experience. Meeting new people at the Manufacturer and Associate Sponsored Hospitality Suites, networking over breakfast, participating in the Fish Bowls, and making connections while lounging poolside or on the beach, what could be better? I had an absolute blast last year, and I can’t wait to do it again this year. See you in Colorado!

NAHAD President Jim Reilly invites and encourages attendees to take advantage of all the convention has to offer.

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ENERGY EFFICIENCY

Ron Marshall • For the Compressed Air Challenge

When “automatic savings” costs you money A fabricator of copper tubing products had a large and expanding plant with three separate compressed air stations located in three different areas. One area was constantly complaining of chronic low pressure events, so the maintenance staff decided to install an extra compressor in a fourth location, complete with air dryer and receiver. The plant staff started the unit and let it run, content that the problem would be solved.

The compressor they chose had a basic electronic control with minimal status outputs. This compressor ran in the quiet corner of the plant for many years, in a trouble-free manner. Maintenance staff indicated that it was the best compressor of the bunch.

An air auditor did a walk-through assessment of the compressed air systems.

When he started checking the extra

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compressor, he scratched his head. The compressor was obviously running, but its output line was cool to the touch. A check of the amps showed lower-than-rated values. The auditor came to the conclusion that, although running and consuming considerable power, the compressor was not producing any air because it was in the unloaded condition.

A check of the operating hours showed the compressor had minimal loaded hours—most of the compressor life had been spent running unloaded. Operating costs in this position were estimated at $9,000 per year.

The auditor placed the compressor in “auto” mode and it immediately timed out and shut off, for the first time in many years. Plant operating staff personnel were intrigued by what this “auto” setting was all about, and were duly informed. The unit

now sits armed ready to start on occasional low-pressure events, but it times out and turns off when not required. It turns out adding the compressor’s storage receiver to the system solved most of the low-pressure complaints.

Learn more about compressor controls in our next Compressed Air Challenge seminar in your area.

FPW

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Edited by: Mike Santora • Associate Editor

DESIGN NOTES

Direct stroke measurement for hydraulic cylinders Whether it’s agricultural machinery, construction equipment or municipal vehicles, intelligent sensors are indispensable nowadays throughout the mobile machine market. Recording paths and angles is an integral component of intelligent operating functions. These functions improve not only the convenience, but also the safety of mobile machines. Using intelligent sensors also increases the performance and efficiency of mobile machines, allowing repetitive work processes to be automated.

Measure and monitor motion sequences As most motion sequences for mobile machines use hydraulic cylinders, one of the most important measurement tasks for sensor technology is determining the stroke of the cylinder to enable measurement and monitoring of the motions. No wonder then, that both machine and sensor manufacturers are always looking for new innovations in stroke measurement for hydraulic cylinders.

This need prompted SIKO to develop the SGH10 measurement system for direct stroke measurement in hydraulic cylinders. The cylinder stroke is measured using Bowden cable sensor technology installed directly in the cylinder, and the plug ensures the system is fully IP69 protected.

The SGH10 cylinder stroke measuring system pursues an entirely different technological approach than some other measuring systems based on magnetorestrictive, inductive or Hall-based technology. In contrast to these systems, a Bowden cable mechanism installed directly in the cylinder is used to measure the stroke.

The cable of the Bowden cable mechanism is

The SGH wire-actuated encoder measures the absolute, direct cylinder stroke in the hydraulic cylinder. The SGH10 is pressure resistant up to 300 bar with pressure peaks up to 500 bar and also has an operating voltage from 9 to 36 Vdc.

mounted in the piston head. If the cylinder is extended, the cable, which is wound up in a cable drum, is pulled out. The rotation of the cable drum is then detected without contact by the sensor electronics and used to calculate the linear travel. This process makes it possible to detect the position of the cylinder precisely at all times.

The magnets that are used to detect the rotation are scanned by the electronics through the pressure-resistant base plate of the SGH10. The electronics are fully encapsulated on the unpressurized side of the system. This means the entire measuring system is built into the cylinder and is protected from environmental conditions.

This provides a clear advantage: In contrast to a measuring system mounted externally on the cylinder, the sensor system cannot be damaged by loose parts.

FPW

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Piston drilling unnecessary Another aspect is the reduction of costs for integrating the system into the cylinder. This www.fluidpowerworld.com

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is because in previous measuring systems, the sensor rods had to be integrated into the piston over the entire measuring path; this often required long and highly precise bore holes in the piston. This is not only expensive, but also weakens the structure of the piston. In the SGH10 stroke measuring system, just one small thread is needed in the piston to mount the cable. This allows the system to offer overall cost savings for hydraulic cylinders.

SGH measuring technology can also be used in telescopic cylinders. The technology provides design engineers with options when developing assistance systems and supplemental functions in mobile machines.

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DESIGN NOTES

Safety dampers protect linear modules from runaway motion

The Omega module from Bosch Rexroth is used in applications involving handling, assembly and general automation. Safety dampers from ACE are used in the end positions.

From pick-and-place equipment to linear transfer lines, moving work pieces and finished products from point A to point B is a major part of today’s production environments. In many cases, speed, precision and safety are top priorities. Protecting both operators and equipment from impact forces is a critical task— one that is often accomplished with shock absorbers and safety dampers. In the case of linear modules that must endure high speeds and loads, safety dampers provide insurance against impact damage.

Michigan-based ACE Controls designs safety shock absorbers to protect people and equipment in emergency stop situations.

With up to 300% higher capacity than traditional shock absorber designs, ACE’s SCS33 to SCS64 dampers enable true linear deceleration to protect machinery. An upgraded orifice design creates a higher capacity in a more compact size. These safety dampers are more suitable for applications on automatic transfer machines, robot systems and other applications where uncontrolled motion could result in damage or danger.

These safety dampers were recently chosen to provide extra insurance for a widely used linear module assembly. The Bosch Rexroth Omega modules feature drive components on the carriage, 20

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enabling a variety of configurations used especially for long strokes in either a vertical or horizontal position. In this particular module, there are three sizes with main body widths of 55, 85 and 120 mm and lengths to 5,500 mm. The repeatability and rigidity of this module make it well suited to long strokes with speeds to 5 m/sec and accelerations to 50 m/sec2.

However, some end users of this linear module system require extra insurance against runaway motion should an unforeseen emergency occur.

Due to the loads and speeds involved in many linear motion applications, the module’s design engineers wanted to create an optional industrial impact damper to protect the Z-axis against uncontrolled motion. Working together with ACE engineers, safety dampers were carefully designed over a nine-month period to work perfectly with the linear modules. Compared to standard hydraulic industrial impact dampers, ACE safety dampers were specifically designed for emergency use only. In this scenario, three load ranges from 20 to 90 kg, at impact speeds to 5 m/sec, had to be accounted for.

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Safety impact dampers like the SCS-series from ACE can act as an

Several hydraulic safety dampers were considered.

A slightly elevated impact speed was assumed in all cases to give the linear modules some flexibility. While the SCS33-50 impact damper with maximum energy absorptions of 620 Nm per stroke would have worked for the lower load ranges, the calculation showed that the larger SCS45-75 was needed to handle the higher moving mass (maximum 90 kg) for the 1,654.6 Nm per stroke. The result was that the linear modules were now more than capable of providing reliable service in an emergency.

alternative to industrial impact dampers to protect linear modules and systems.

FPW

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FUNDAMENTALS

Josh Cosford • Contributing Editor

A primer on pressure We fluid power industry professionals probably take pressure for granted. If I asked any of you to define pressure, you would say force over a predetermined area. We all typically use similar units, such as pounds per square inch (psi) or Newtons per square metre (Pa), but pressure isn’t confined for use in the fluid power industry alone (no pun intended). Pressure exists everywhere at all times, and even the most remote location in outer space will still have a few atoms of matter loitering around to ruin a perfect vacuum.

I’m going recap week one of hydraulics night class, so forgive me if this is redundant.

The gases held close to the Earth’s crust by gravity have enough mass to create pressure around us at all time. This atmospheric mass is enough to exert 14.7 lb on every single square-inch plane equally in every direction.

Think about that for a moment. If you held your hand out flat with your palm up and we could magically create a vacuum under the other side of your hand, you would have in the realm of 400 lb pushing down on your hand.

Go ahead, hold out your hand. You, in fact, do have 400 lb pushing down on your hand (give or take, depending if you have hands like a toddler or pro-wrestler). You do not feel 400 lb pushing down on your hand because there is also 400 lb pushing up on your hand, and that is the nature of fluid pressure as define by Blaise Pascal: “when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.”

Around you right now—if you live at or near sea level—are 14.7 lb per every single square inch of your body, in every direction inward to your body and every direction outward from inside your body. Force from an infinite number of directions pushes equally and opposite to an infinite number of places on your body due to the isotropic nature of a liquid or gas. But why? Why does the mere 22

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existence of air molecules around you cause them to push on each other and your body?

There is some epic science going on at the atomic level to explain the nature of pressure. You can’t see air molecules up close because they are smaller than the wavelengths of visible light passing around them, although with enough air molecules—we’re talking an atmosphere worth—you can see the compound result of countless diffraction events creating our beautiful blue sky. However, just because we can’t see air particles, it doesn’t mean they’re not busier than a border collie with ADHD and a caffeine addiction. I’m going to refer to air atoms and molecules as particles from here on out.

The motion of atoms in a fluid is dynamic and incessant. Their motion is complex, but air particles essentially travel in a straight path until they smack into a solid object or hit other air particles. After hitting something, the particles deflect, reflect and generally bounce around like undiminishing-energy squash balls trapped in a box, as seen on page 23. Their energy to create pressure, for the most part, remains constant. Energy is not wasted as heat in the “Brownian” chaos of particle movement; any kinetic motive being converted to heat as a result of these smashing particles results in an equivalent excite-

ment of motion, conserving energy entirely.

Particle movement creates heat, and heat creates particle movement, both of which maintain pressure.

The pressure created from a mass of fluid is different from the pressure created from a solid. A solid object will apply pressure only in the direction of its force vector, such as an anvil being pulled to the centre of the Earth, usually landing on Wile E. Coyote’s noggin. However, if you put your finger to the side of the anvil, the only pressure is a result of the force applied by your finger, and only in the direction of the push.

Atmospheric fluid pressure (remember, air is a fluid, as it can take the shape of its container) is a result of the mass of the air column extending up to outer space. If you placed a weightless, one-inch square tube extending to the top of the troposphere, used the giant vacuum from Spaceballs to suck away the rest of our atmosphere, and then weighed your tube, you would find it weighed 14.7 lb. I find that fact amazing, especially considering the air around me provides no perceivable effect of mass on me whatsoever.

Pressure in a fluid power system isn’t much different from atmospheric pressure,

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FUNDAMENTALS only that there is more of it. By packing more matter into a smaller area, we are able to create more pressure. In a pneumatic system, the increase in pressure is directly proportional to the number of particles crammed into the same sized space. Twice the particles moving with the same energy means twice the impacts on the walls of the container, exerting twice the pressure.

A hydraulic system doesn’t need nearly the same increase in particles to create exponentially more pressure. In a sealed pressure vessel measuring zero gauge pressure, we need just one percent more molecules to be packed into the same space to increase gauge pressure to 2,000 psi. Doubling the number of molecules of hydraulic oil in this pressure vessel would result in an increase in pressure to well over 200,000 psi on our pressure gauge. Fun fact: if we sank this pressure vessel to the bottom of an 86,580-ft sea on a remote planet in a galaxy far, far away, gauge pressure would drop to zero as it equalized with the 200,000-psi of surrounding water pressure.

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TRAINING

David Marlowe • Owner/CEO • DMAR Technical Training and DMAR Business Centers USA

Hydraulic fixed-displacement pumps

In my continuing series on a mechanic’s guide to a hydraulic system, we have already discussed the importance of the fluid’s viscosity, cleanliness, flow rate, cooling and reservoir level to ensure a positive head pressure (NPSHA) to the suction side of the pump.

Now, it’s time to discuss the heart of the hydraulic system—the pump.

Proper selection and operation of the pump will have a major influence on the system’s overall performance, operational efficiency and operational cost.

In all pump classes, you will hear “Pumps don’t suck nor do they pump pressure.” Although pumps come in a variety of shapes and sizes with different operating mechanisms, they all do one thing— create flow by transferring mechanical energy to fluid velocity.

Images courtesy of Muncie Power Products Inc.

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To understand this, we must first know that the energy comes from the motor. The motor takes electrical energy and converts it to a twisting force known as torque. There is a relationship between horsepower, speed and torque. The formula to the right will make it clear.

Torque is the mechanical energy that is transferred from the motor shaft to the pump shaft and then converted to velocity in the fluid.

Because the pump has a maximum speed rating, most industrial hydraulic systems use either a motor with a nominal rating of 1,200 rpm (actual 1,140 rpm) or nominal rating of 1,800 rpm (actual 1,750 rpm).

On mobile hydraulic systems that use internal combustion engines, a variable drive is used to regulate the output speed. It is important that the operators do not drop below the minimum or exceed the maximum speed limit of the pump.

horsepower (hp) X revolutions per minute (rpm) = torque Constant (5,252 ft-lb; 63,000 in.-lb)

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The pumping action of any hydraulic pump can be understood if one understands Boyle’s law: Boyle’s law—at constant temperature for a fixed mass, the absolute pressure and the volume of a gas are inversely proportional.

Simply stated, when the volume decreases, the pressure increases (discharge stroke). When volume increases, the pressure decreases (suction stroke).

Where a dynamic (centrifugal) pump’s capacity (gpm) will go down as head pressure increases, a positive displacement pump delivers a constant output flow (gpm) regardless of the head pressure.

The size of a positive displacement pump is expressed in terms of the number of cubic inches displaced during one revolution of the drive shaft.

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Another method of representing the size of a positive displacement pump is the nominal flow at a specific drive speed. Hydraulic pump manufacturers simply refer to these pumps sizes as 8 gpm, 10 gpm, and so on.

In theory, a pump that displaces 25 in.3/rev will deliver 25 in.3 of fluid for each revolution. In actuality, the pump output will be reduced due to internal slippage (the fluid flows from the pump’s output to the pump’s input). For a given clearance, the higher the outlet pressure, the higher the slippage.

Volumetric Efficiency = Actual Flow x 100 Theoretical Flow

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The mechanical efficiency can be found by dividing the theoretical torque value by the actual torque required to drive the pump.

Mechanical Efficiency = Theoretical Torque x 100 Actual Torque Overall efficiency includes both volumetric and mechanical efficiencies.

Overall Efficiency = Volumetric Efficiency x Mechanical Efficiency 100 It is important that the operator and maintenance personnel have a thorough understanding of these values and how they relate to their system.

Multiple applications exist where fixed-displacement pumps do the job. Fixeddisplacement pumps can be selected for use as long as the following conditions don’t need to be met: • maintains system pressure on a stalled actuator • during operation of the cycle, the actuator must be operated at relatively low speeds • circuit operates at varies speed ranges • the pump is unable to unload by the circuit It is imperative to select a pump of precise size. A fixed-displacement pump is a positive displacement type where the amount of displacement (gpm) cannot be varied, only by changing the drive speed to the pump. Since industrial hydraulic systems are usually driven by constant speed electric motors, applications of a fixed-displacement pump are limited. In the next article, I will discuss the different types of fixed-displacement pumps and their applications.

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SAFETY

J. Eric Freimuth • Hydraulic Training Associates

Lockout of hydraulic systems can save your life Hydraulics is all about the transmission of energy to perform work. As we discussed in our December article, accumulators store energy that can be used during power failure or when additional energy is needed.

In certain situations, additional flow may be needed, so an accumulator can be used to supplement the flow rate of a pump. Unless dispensed of properly when working on a machine, anyone who manages to get in the way of the released energy could be injured or even killed.

Energy is not always obvious through your sense of hearing, smell, taste or sight; energy can elude all of our senses. To this end, lockout is a recognized systematic approach to controlling all forms of energy that may harm workers. The energy used in machines to perform work is relatively safe to personnel—as long as there are safeguards. At some point, personnel must interact with machines on an upclose and personal level, for such things as maintenance. It is at this time that uncontrolled energy becomes extremely hazardous to workers.

Understanding lockout while also being aware of the difficulties that can be found in the energy isolation and control of hydraulic systems is critical to safe machine operation and maintenance. Additionally, hydraulic energy can be an extremely difficult thing to isolate. The medium of a fluid under pressure is always seeking a way out of its confines. Crushing injuries are the most common injuries caused by exposure 28

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Proper machine identifications and padlocks are crucial to lockout/tagout programs for machine maintenance. Image courtesy of IDEAL INDUSTRIES to hydraulic equipment where hydraulic fluid under pressure was not controlled and the mechanical component was not mechanically secured.

Lockout is a process of steps that are taken to safely control energy. Lockout is also about maintaining the security of having energy controlled over the duration of time.

The thought that comes to mind is the

padlock, which is only part of a much larger undertaking of sequences that is considered safe.

Machine manufacturers are required to integrate devices into their hydraulic system to allow the control, verification and isolation of energy at the design and manufacturing stages. Advances in laws and legislation have produced integration companies that

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Demonstration of how to lock out a ball valve. Image courtesy of CD Industrial Group

specialize in conforming machines to meet machine safety regulations.

In many cases, testing and verification of hydraulic energy requires extremely precise measuring instruments. Much like multi-meters used for testing electricity, pressure testing equipment is used for hydraulic energy verification and is important in determining a “0 Energy State.”

As little as a couple psi will generate extreme forces in a large bore actuator.

There have been numerous occasions where isolating devices have failed. Energy leakage through locked out isolation valves is possible. (The definition of isolation is the process of separating one thing from another; the purpose of isolating a hydraulic system is to protect one from hazardous energy sources.)

Methods such as lockable or monitored isolation valves are common ways to isolate hydraulic energy. This is most common in non-centralized hydraulic systems. Unlike centralized hydraulic systems, which are relatively easy to work on, doing work on a non-centralized system can consume a large amount of resources and time. Isolating a work area for a specific task is possible; however, it is critical that personnel are knowledgeable of the system and it is also critical that there are isolation devices integrated into the system. It must be known though, that energy will be present on one side of the isolation device using this method.

The accidental release of hydraulic fluid under pressure is most common in non-centralized systems. This is because there is a vast array of piping, tubing and interconnections in a noncentralized system. The accidental breach

of interconnections containing hydraulic pressure is one of the highest leading causes of injury and environmental damage.

The accidental breach is usually caused by personnel: • standing on a machine • disconnecting a machine • dropping large components on a machine • connecting rigging for hoisting • burning through and cutting through a machine • completely removing fluid under pressure in a machine The most common and favorable method of controlling hydraulic energy is to remove it completely. This is accomplished by the following: 1. shutting down the prime mover that drives the pumps 2. moving the actuators to a parked position 3. removing and supporting any overhanging loads 4. bleeding off all residual or trapped pressure 5. bleeding down accumulators 6. testing and verifying through specific procedures All participants must have a clear understanding of the procedure for group lockout prior to the lockout commencement.

Group lockout boxes should remain in the open position until ready, and be retained by the authorized individual to prevent the accidental locking of a lockout box prematurely. www.fluidpowerworld.com

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It’s becoming common for companies to develop and post lockout procedures specific to individual equipment. Media such as placards, documentation and even training videos are used to train individuals in the duties required for an effective lockout. Step-by-step checklists are highly effective, not only for lockout, but also for the safe return of energy to the machine.

The procedures of a lockout program may contain the following elements: • identification of the machine, its location and a description of what it does • list of steps required for shutting the machine down • procedures in the shutdown process that will assist in releasing loads and stresses in the mechanics, such as pinning and blocking, and release of hydraulic pressure through the controls • identification and location of energy isolation devices and their sequential use • locations for lockout devices such as padlocks Developing and educating all personnel and performing a rigid lockout/tagout procedure for all equipment will assist in saving lives and injuries.

Neglecting to perform this procedure one time may mean the difference between injury and/or death.

FPW

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MAINTENANCE

Mary C. Gannon • Managing Editor

Follow these 5 simple tasks

for efficient hydraulic fluid management Just having a fluids management plan in place doesn’t mean that you are doing it correctly. Managing your lubrication properly is critical in maintaining clean, efficient hydraulic systems, said Jason Kopschinsky, CMRP, director of reliability services for Des-Case.

“Not approaching lubrication in a holistic manner, including lubricant specifications, education, contamination control, preventive maintenance optimization, proper storage and handling, and condition monitoring, is poor lubrication management,” he said.

With that said, Kopschinsky offers five tips to ensure your hydraulic fluids have a long, clean life and keep your machines running as they are meant to.

1

Optimize your lubricant inventory. Maintaining cool, clean hydraulic fluids starts when you receive new fluids. Kopschinsky said you should label your fluids clearly with color-coded lubricant tags to avoid cross contamination and comply with OSHA requirements. Some manufacturers provide a complete management system with specific colors and shapes on labels for specific types of fluids. This ID system should be applied to all tanks, top ups, funnels, application points and so on, said Kopschinksy.

Storage and organization is critical in hydraulic fluid maintenance. If you’re storing your barrels in open, dirty spaces, the fluid can easily get contaminated. An organized, well-labeled and coded lubrication room simplifies fluid storage and ensures clean-running systems.

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2

Organize your fluid storage. Labeling your fluids adds little value if they are not stored properly, said Kopschinsky. This starts in the lubrication room, which should be clean and organized, with closed containers. Not only will this reduce contamination, it will reduce waste as well.

3

Make minor equipment modifications. Simple devices such as desiccant breathers, sample valves and sight gauges can go a long way in maintaining a clean, efficient system. They allow for easy inspections and screening. This will help ensure your fluid is long running and contaminant-free for its intended life.

“Modifications like this help maintain a totallyclosed system while excluding and removing contamination,” Kopschinsky said. “They also ensure repeatable, efficient results and promote enhanced equipment and component reliability and performance.”

4

Give clear, precise instructions. ‘Sample fluid’ is not a procedure. “Maintenance procedures must be readily accessible at their point of use, and must contain a list of tools and supplies, cautions and warnings, and task-specific details,” Kopschinsky said.

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5

Make data-driven decisions. According to John S. Mitchell, author of the book Physical Asset Management, “When evaluated on a benefit/cost basis, approximately 50% of preventive maintenance tasks have essentially no value.” For example, time-based oil drains not only waste fluid that might still be clean and useful, but they also waste labor and time. This too, can cause environmental impacts by disposing of more fluid than is necessary in your facility.

In the end, said Kopschinsky, “Increasing lubrication PM frequencies without calculating the required frequency is poor lubrication.”

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New twist on

pneumatic muscles Researchers are taking advantage of light, yet powerful pneumatics to improve life for pediatric patients.

Ken Korane

Contributing Editor

The Center for Compact and Efficient Fluid Power

(CCEFP), a network of researchers, educators, students and industry experts, is helping advance hydraulic and pneumatic technology and developing fluidpower systems that are smaller, lighter and better-performing than anything currently available.

One CCEFP-sponsored project that aims to meet those goals, Soft Pneumatic Actuator for Arm Orthosis, has researchers at the University of Illinois at Urbana-Champaign (UIUC) and the University of Wisconsin-Milwaukee developing a new type of orthotic support powered by novel, flexible actuators.

Novel, soft air actuators used in a sleeve orthosis (not shown) have a spiral design that contracts and supports the

Flexible orthosis

arm.

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According to Elizabeth Hsiao-Wecksler, professor of Mechanical Science and Engineering at UIUC, the overriding goal of the project is to develop a light, soft wrist orthosis for pediatric patients who use crutches for mobility. While walking with crutches, peak loads in the wrist typically approach half of body weight and the wrists are loaded at extreme angles. Repetitive, high loads and poor wrist postures can to lead to joint pain, carpal-tunnel injuries and similar afflictions.

Unfortunately, pediatric crutch users often must resort to wheelchairs when 2• 2016

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their arms cannot support their body weight as they grow and effects of these secondary injuries worsen. Ultimately this reduces mobility, fitness and quality of life.

A light (less than 1 kg), pliable, pneumatically powered wrist orthosis could selectively constrict motion to provide the needed support and transfer loads from hands to forearms during crutch use. That, in turn, would reduce transient loads and associated stresses by 50% and give wrists a more-comfortable posture, therefore lowering the risk for joint injury, explained Hsiao-Wecksler. The device would also allow for normal hand and arm movement when at rest. Such an orthosis is noninvasive and requires no customization, as it readily adapts to the contours of the wearer’s arm.

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A soft wrist orthosis for pediatric crutch users relies on pneumatic artificial muscles to aid mobility.

Simple modifications would also allow the orthosis to be used in auxiliary, or underarm, crutches. Thus, others with acute leg injuries or who face post-surgery recovery would also benefit from the new design.

Novel pneumatic muscles

A key to the project’s success involves the method for powering the device. To that

end, researchers have developed innovative pneumatic actuators called Fiber Reinforced Elastomeric Enclosures (FREEs).

FREE actuators are similar in construction and operation to pneumatic artificial muscles (PAMs), also called McKibben actuators. PAMs are fiber-reinforced, flexible elastomeric tubes that contract and generate tensile force when pressurized (typically with air) and rebound to their

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initial length when exhausted. Commercial McKibben actuators include the Fluidic Muscle from Festo and the Air Muscle from Shadow Robot Co.

However, typical PAMs only provide linear motion and force, explained Girish Krishnan, professor of Industrial and Enterprise System Engineering at UIUC. This project expands the capabilities of McKibben actuators by altering their construction to yield different deformation patterns, said Krishnan. Such FREEs permit motions beyond pure extension, including contraction, axial rotation and, more generally, screw motion or simultaneous translation and rotation.

FREEs are made with two sets of inextensible fibers wound in a helical fashion around an elastomer tube. The orientation, or helix angles, of the fibers can vary widely in FREE actuators. Selectively altering the helical angles yields complex deformation patterns when the actuators pressurize. In the orthosis, said Krishnan, the current design involves a spiral design that contracts and holds on to the arm, providing relatively uniform pressure and support on the forearm.

Analysis breakthrough

An important aspect of the project involves fundamental research that expands the knowledge base for understanding how FREEs work and creating modeling tools for designing them, said Krishnan. Current McKibben muscles are based on simple fiber orientations and have well-established, mechanics-based mathematical models to predict their behavior.

To help generalize the construction and operating principles for FREE actuators, the CCEFP group has developed a new method to analyze the deformation behavior of FREEs that involves kinematics and kinetostatics.

As noted above, a FREE is essentially a cylindrical hyperelastic membrane with two sets of inextensible fibers wound helically on its outer surface. When pressurized, the actuator tries to maximize its enclosed volume while the fibers maintain a constant length.

Therefore, the analysis considers a volumemaximization problem with constraints due to the inextensibility of fibers, according to the researchers.

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The pneumatic orthosis has the flexibility to allow normal hand movements.

After kinematic analysis, they added a material model of the elastic tube for elastokinetic analysis of the actuator. This gives force-versus-displacement and torqueversus-rotation relationships under various pressures. This offers an alternative way to analyze McKibben actuators. But it also analyzes FREE actuators with asymmetric fiber angles for which, previously, there were no known models. This development lets users readily consider various alternatives and design the FREE geometry, construction and material to meet specific stroke and force requirements.

“This is a major contribution to the CCEFP project,” said Krishnan. Prior to this, most literature only considered McKibben actuators, which primarily contract like muscles. “We have extended this to any fiber configuration. It doesn’t limit motions to pure contraction, but also to extension, rotation, and screw and helical motion, which is what we are trying to demonstrate,” he said.

Creating a general model beyond those for McKibben actuators will let users analyze a more-general class of pneumatic actuators, making them useful for various other applications.

“Considering that these actuators are quite soft, the model predicts motion really well, within 3% accuracy,” Krishnan said.

However, current methods allow a bit more leeway when predicting force, primarily due to estimated properties of the actuator’s constitutive elements.

Fabrication and testing

To make prototype FREE actuators, technicians use a custom winding machine that can interlace fibers to the elastomer tube at any required angle. Adhesive binds fibers to the tube. Several types of fibers were considered—for instance, common cotton twine gave good performance—but Kevlar proved to be the best option, Krishnan said.

He also noted there are no significant technical hurdles to larger-scale production.

The designs, materials and fabrication processes are rather straightforward and can be readily expanded. Commercial ventures like Festo and Shadow have tried-and-tested methods for manufacturing flexible actuators, although those products are mainly used in high-force robotic applications, said Krishnan. “We’re trying to demonstrate more functionality beyond just force, such as different motion patterns.”

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The prototype actuators will be integrated into pneumatic sleeve orthoses to assess performance, safety, comfort and efficiency. Testing with patients is slated for this spring.

To power the pneumatic sleeve, Hsiao-Wecksler’s group is also pursuing the possibility of harvesting pneumatic energy during motion by designing a small pneumatic pump that mounts in the tip of the crutch. The resulting pressurized air can be stored and used to replace an external source of pneumatic power. Prototype FREE actuators are about 15 in. long and 0.38 in. in diameter, so inflated volume is quite low, and pressure requirements are in the 30 to 40 psi range. The pumping action might also provide shock absorption and add compliance to the crutch to improve user comfort.

Future applications

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performing pick-and-place tasks, as well as reaching, gripping and twisting. They’re especially suited for applications that involve human contact. Being made of inflatable materials, they can easily interact with humans and cause no harm, even if there is unforeseen impact, said Krishnan.

McKibben-like actuators that spiral or rotate might someday even replace conventional pneumatic motors and rotary actuators. Given the wide range of possible motions, engineers are only scratching the surface of potential applications.

Other potential applications for FREE actuators are also on the horizon. These soft, compact, lightweight, high-force and energy-storing pneumatic actuators have the potential to revolutionize portable medical assistive devices such as powered prosthetics and orthotics.

“One straightforward application we foresee is in a powered upper-extremity orthosis, say in a patient-transfer device,” said Krishnan.

Nurses or aides lifting a heavy patient could wear a pneumatic stiffening sleeve that can actually supplement the force their muscles provide. A prototype is under construction.

The capabilities of FREE actuators also lend themselves to use in robots, such as

FPW

CCEFP ccefp.org

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From the basic to advanced:

selecting directional control valves Scott Knaack

Sr. VP of Sales and Marketing Prince Hydraulics

Manual control of stack valves via handles is ideal if space is not an issue but cost is.

Images courtesy of Prince Hydraulics Corp.

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Directional control valves are fundamental components in any hydraulic system, but these workhorses have evolved from simple to sophisticated designs that lower system cost.

Hydraulic directional control valves have always been fundamental to hydraulic circuits, machinery and equipment, but an increase in technology is bringing a new level of performance, sophistication and efficiency to these crucial workhorses. Today we see things such as fine metering spools, load sense, proportional features and remote controls to shift spools. All of these features can provide more control, more efficient use of the valve and energy savings. These features, in turn, help lower operating costs.

Directional valves have been used for many years. They can range from being simple, low-cost and compact to ultra-sophisticated, multi-section instruments with price tags to match. Whether you need a single-spool valve to operate a log splitter or a stack valve with 8, 10 or even more work sections, you will be able to find, or configure, a valve with the options that allow it to work in the application needed.

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Critical design considerations No matter how complex a valve might become, it is important to keep in mind a few basic ideas. A valve essentially consists of a spool inside a casting that is either controlled mechanically or electrically. Directional valves come in two main categories: either a sectional valve (sometimes called a stack valve) or a mono block design.

Sectional valves offer far more flexibility, options and complexity, while mono block vales are usually more economical as well as smaller in physical size.

“The most common circuit is the parallel circuit. In this design, when any one of the spools is shifted, it blocks off the open center passage.”

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Be sure to research the following considerations before choosing or designing a directional valve: • Is it a parallel or tandem circuit?

• Do you need an open- or closed-center for oil flow?

• What is the number of gallons per minute from the source?

• How many directions do you want the oil to flow (this is referred to as spool type and is usually expressed as three- way, four-way)?

• How many handle (spool) positions do you want (usually three-position or four-position)?

• What is the spool action, such as spring center to neutral or various detent selections?

• And finally, do you need the valve to be manually or electronically controlled or both?

Mono block valves are usually simpler and smaller in design, and more economical for less complex applications.

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The most common circuit is the parallel circuit. In this design, when any one of the spools is shifted, it blocks off the open center passage. Oil then flows into the parallel circuit core, making oil available to all spools. If more than one spool is shifted, the oil will flow to the path of least resistance. When a spool is shifted in tandem, also referred to as a priority circuit, oil is cut off to all downstream sections.

Thus, the section nearest to the inlet has priority over the other sections. If more than one spool is shifted, all the oil will go to the section nearest to the inlet.

Know your flow, ways for optimal use A hydraulic system will either have a fixeddisplacement pump (gear pump)—which requires an open-center valve—or a variabledisplacement pressure-compensated pump that limits pressure. In the latter case, you need a closed-center valve. Typically, an open center can be converted to closed center by adding a closed-center plug in the outlet section. This will block off the opencenter core when the spools are in neutral.

The flow of your source is necessary in determining how small or large of a valve is needed for your application. Typical sizes range from 2 to 40 gpm. If you size your valve too large, you could have trouble shifting the valve and are adding unnecessary cost. If you size your valve too small, you risk over-pressurizing your system and building up heat. Excessive heat is detrimental to hydraulic systems.

The number of ways you want the oil to flow is sometimes referred to as the spool type, as mentioned earlier. To expand on that, you may have either a three- or fourway spool. An example of a three-way would be: pump, return and work port. An example of a four-way spool would be: pump, return, work port and work port. The spool type is the number of different positions for the spool. For example, a three-position would be forward, neutral and reverse. An example of a four-position would be forward, neutral, reverse and float. You also have to consider

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the spool action. Two common actions are spring center and detent. Spring center allows the handle to pop back to center when released and detent leaves the handle in place once it is moved.

You can control the shifting of the valve by either using a handle (manually) or solenoid (electronically). If the application is cost sensitive, manual is the obvious choice. The electronic option is controlled by a solenoid and allows remote electrical on/off control. As systems become more demanding, there has been a push for more electronics to go into directional control valves.

Directional control valves have always been a fundamental part of any hydraulic system.

Now they offer features and functions that make them more productive and efficient than ever. These evolving features and functions of hydraulic control valves in the future will only be limited by our imaginations as users’ demands and technology continue to push the envelope forward.

FPW

Prince Manufacturing princehyd.com

Electronic or solenoid control of stack valves allows remote electrical on/off control for more complex applications.

Discuss This and other engineering topics at www.engineeringexchange.com

Valve assembly eliminates pressure compensated pump to lower overall system cost A breakthrough valve assembly design from Prince Manufacturing includes inlets that offer pressure-compensated characteristics without the need for an expensive pressure-compensated pump. Additional inlets manage the flow and allow high-flow tractor pumps to be used with nominally sized valve assemblies.

From an operator’s perspective, it gives them the control they want for the work that needs to be done but at a lower cost.

Typically, fine hydraulic control comes from a load-sense valve as well as a high-end pressure compensated pump, both of which are relatively high cost.

Through the use of specially designed compensated inlets, Prince’s engineers have been able to achieve customized flow to the valve sections, allowing highly-controlled function of the section by the operator…all with standard fixed-displacement pumps. The inlets also offer filtered pilot flow for solenoid operation in less than optimal oil cleanliness conditions. Solenoid operators are available in open center, load sense, load sense– pressure comp and proportional configurations.

Other customized inlets and outlets can offer a variety of specialized features to optimize customer requirements.

Customized solutions are available at relatively low usage levels.

All of this is intended to give the operator fine control of all the hydraulic functions of his rig without the extra cost associated with the typical hydraulic systems of today. This represents a significant savings when compared to traditional pressurecompensated pumps.

These new valve assemblies also feature optional radio frequency control integrated solutions for maximum easeof-use. A 2-, 4-, or 8-button remote or, if needed, a belly pack type of remote can be supplied with more options and features.

Prince also offers as options for more corrosive environments, composite end fitting of the valves and enclosed handles that are conducive to harsh conditions.

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Taking a methodical approach is the best way to get off-highway equipment working again, quickly and safely.

Mobile hydraulics troubleshooting Carl Dyke • Contributing Editor

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It is inevitable that even a well-designed mobile hydraulic system will malfunction at some point. There are many reasons why it might happen. Contaminants in the fluid may be interfering with normal component functions. The machine may have been used beyond its design limits at some point. Regular maintenance may have been overlooked or a component such as a pump may have been operated past its expected service life. One component in the system may turn out to be less durable than expected by the designers. These are just a few of the common reasons for system faults.

Once a mobile machine is no longer functioning normally, it is common for the next branch of activities and decisions to become quite abnormal or even suboptimal. In this two-part article, we’ll look at how a typical troubleshooting cycle might progress from beginning to end, how it might become quite random and inefficient, and how it is possible to stay organized and on-track.

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Operator’s complaints Troubleshooting will likely start after a complaint from the machine operator. The operator may notice that functions have become slow. Maybe it’s the boom lift on a crane, or the bucket curl function on an excavator. Perhaps winch speed or travel speed has become slow. Another potential problem is that a cylinder or motor is moving too quickly. These are problems related to the rate of flow.

Another type of complaint is a problem with lifting the heaviest of normal loads. The cylinder or motor motion for the lift function stalls completely under these loads. If the machine has hydraulic propulsion at the wheels or tracks, the equivalent fault would be stalled motion on steeper slopes—ones that can usually be climbed without difficulty. Instead of a complete motion stall, the issue might be an uneven, hunting motion at the cylinder or motor. These types of complaints often point to a problem achieving pressures in the normal, maximum range.

Another range of faults might include one machine function that will not operate at all, or perhaps the cylinder will move only in one direction.

A final example is a hydraulic motor or cylinder that is creeping or in full motion when the controls are placed in neutral/hold position. These issues are often thought of as directional problems.

We have described a range of faults in three different categories, any of which would frustrate a mobile machine operator who was expecting a normal day at work.

The temptation for some troubleshooters under downtime pressures might be to go deeply into the heart of the hydraulic system, replacing a pump or a main valve. That would be jumping far ahead in a process that needs some thought and care. A methodical process will usually consume less time and will avoid needless component replacement.

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The technician as investigator So, how does a troubleshooter start the process? Start with the operator who filed the complaint. A shop technician might receive a work order with a simple description of the fault. The complaint may not be described as clearly as the earlier examples.

Hours may have elapsed since the machine was taken out of service. Find that operator if possible and ask questions.

This is a great time to adopt crime scene investigation skills. You’ll want to ask the operator to explain the fault. Let the story emerge naturally, but interrupt when you need more specifics, such as what type of material was being excavated, or whether the load to be lifted was a usual and normal load. If the operator uses a vague word such as “sluggish” to describe the malfunction, you will want to ask exactly what is meant by that word. You’ll want to know if the problem just happened suddenly or were there other symptoms leading up to the fault in the preceding hours or days. Did the fault occur when the machine was cold at startup, or did the problem only appear once the system was warmed up? Did the operator notice that the hydraulic system was running warmer than usual? Ask if the operator can remember anything else out of the ordinary leading up to the fault. Be patient with this process, listen carefully and take notes.

If the operator reported that his trackdriven machine could not climb an uphill grade of considerable—yet normal—steepness, and then you find a low/high travel speed switch in the cab set in the high

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speed position, you might decide to test the machine yourself or call the operator back to see if perhaps he just overlooked a setting (high-speed travel) that is not meant to work for steep slopes.

What is happening at this stage is called confirming the fault. It is not always possible for a technician to do this easily, once a massive piece of equipment is parked in the shop. If possible, visit the machine on-site soon after a fault is reported so that the symptoms can be witnessed first-hand, and to have the operator’s involvement in the testing. The efficiency of teamwork and trust is valuable in this process.

In some situations, the faulted machine has to be repaired at the job site. The failure will be holding up the progress of work. If, for example, a crane has lowered a load into position on a construction site but cannot lift the hook (hydraulic winch) after being detached from the load, there may be psychological pressure on the troubleshooter to work quickly. The same will hold true for a mining haul truck that is stuck at the dump station with the body hoisted and with no lowering function. A troubleshooter will most assuredly be asked shortly after arriving: How long will it take? This makes for challenging working conditions. In this type of situation, it becomes easy to overlook simple causes for the fault. A troubleshooter must take control of the process and take the time needed to gather important clues and information.

The reason to take the time to gather clues carefully is because it is difficult to know exactly what is going on inside hydraulic components at the time of malfunction. Detailed component testing is time consuming and can be difficult to do safely on-site. Resorting to guesswork component replacement uses up both time and money. What you are trying to do is to gather as many clues from the outside of the system as possible.

Some of those clues may be subtle.

Initial diagnostics: Look for simple causes first Most technicians would agree that it is easier to test electrical systems than hydraulic systems. Safety procedures are still needed of course, but a good quality electrical multimeter can quickly test the internal values of most electrical compo-

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nents at the exposed wiring terminals. Testing related electrical functions on a hydraulic system is one of the tasks you’ll want to carry out sooner rather than later.

Note: In all cases of live hydraulic and electrical testing, be sure to follow all of the machine manufacturer’s safety recommendations. You should already be trained in safe hydraulic work and testing procedures.

But let’s start with even easier, simpler tasks. Of course both operator and technician must always be on the lookout for an external leak. This is the level of simple diagnostics at the beginning of the troubleshooting process. Vibrations can cause some valve solenoid connectors to work loose. Noticing a loose connector or a wire that has become disconnected makes for a short, simple, inexpensive troubleshooting cycle.

If the complaint is numerous slow functions and erratic motions on the machine, and strange pump

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noises, a technician may want to check the fluid level in the main hydraulic tank.

It might be quite low, causing serious flow problems when the machine is working on sloped ground. When were the filters last serviced? Is there a layer of foam on top of the fluid in the tank indicating air ingression? The spongy, non-positive cylinder motion might just be a clamp on the pump suction hose that has come loose, allowing a lot of air to be drawn in. If these points seem obvious, then this is just encouragement not to jump to conclusions too quickly with a decision to change out the pump. Easy-to-check items and issues are often overlooked by great troubleshooters only because of psychological pressure from those waiting for the machine to be fixed.

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Schematic diagram as battle plan If there is no obvious external clue to the malfunction as reported and confirmed— and if a technician has not encountered a particular fault previously—a deeper, more rigorous troubleshooting process must commence.

Don’t bring out the test gauges and flow meters just yet. It’s now time to make a battle plan. The schematic diagram is the most useful tool for planning and guiding troubleshooting work.

In the case of an open-loop circuit, there may be a number of parallel flow paths from the tank out to the pump(s), onward to the directional valves, then to the actuators, and eventually back to the tank. On any one of those main flow paths, there will be valves and other components in series (filters, check valves, flow controls, pressure reducing valves), and there will likely be additional short parallel paths (branches) back to the tank through pressure relief valves.

The schematic diagram is a master flow routing plan, showing the reader where fluid is meant to flow for the different functions, and at different stages of operation. The whole hydraulic system is essentially a circuit, with sub-circuits and

then components. The component symbols are drawn in their normal state as though the machine is shut down. A troubleshooter needs to know the language of the symbols so that she can animate those symbols (for example, shift a directional valve) in her mind’s eye, and study the circuit and sub-circuit flow paths for different stages of machine operation.

The schematic also allows the technician to think about where fluid might flow internally, where or when it should not be.

A piston seal that fails, or a check valve that will not close, may create an internal leak and be responsible for diverting some or all

of the pump flow back to the tank. It is hard to see these possibilities when just looking at collections of hoses, fittings and components on the machine. Mobile machines pack a lot of hydraulic functions into a small space, making it hard to follow and lay out the machine circuit just by looking at hoses and the many strange blocks of steel that they are connected to.

Manifolds are large blocks of aluminum or steel that may have components inserted deep inside, under covers or a plug. They may also feature threaded cartridge valves with part of the component visible from the outside. Valves may also be mounted right on the surface of the manifold. In many cases, manifolds contain all three types of components, making a schematic vital to any real understanding of the circuit.

Sectional valve banks that are common to many mobile machines also contain a number of additional components in each directional control section.

FPW

CD Industrial Group Inc. carldyke.com LunchBoxSessions.com

Discuss This and other engineering topics at www.engineeringexchange.com

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Hydraulic efficiency grows

with variable speed drives Combining hydraulic pumps with variable speed technology increases efficiency while reducing noise and environmental impacts.

Mary C. Gannon • Managing Editor

With any fluid power system, efficiency is always top of the mind, so components and advanced technology that can improve energy consumption are increasingly necessary. To that end, the NFPA last year commissioned a survey to examine the current and potential use of variable speed drives (VSDs) with hydrau-

Siemens’ Sinamics servopump is built on standard components such as the Sinamics S120 drive platform and distributed I/O, and offers users increased machine output and reduced energy costs by up to 50%.

lic pumps.

Overall, a total of 1,788 high-quality usable responses were used to generate results, broken down as 43.1% end users, 10.4% distributors, 14% system integrators, 15.2% manufacturers, and 17.3% other. Almost half (46%) of the respondents had an engineering background. The next largest category was “operations management.” Respondents who chose “Other” were given the option to specify their role; the most common role in this category was “repair and maintenance staff.”

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A hydraulic pump drive, photo courtesy of Parker Hannifin

Not surprisingly, the overall results showed that respondents believe that the use of VSDs in hydraulic applications will increase over the next three years. They cited VSDs’ high-energy efficiency, improved reliability and low operating cost as key determining factors in the increase of their use. On the opposite end of the spectrum, when asked what discourages the use of VSDs, respondents pointed toward high acquisition or upfront costs, lack of maintenance and aftersales support for VSD technology, and lack of design expertise in their use.

The four main manufacturers of VSD technology in the U.S. include Eaton, Parker Hannifin, Siemens and Bosch Rexroth. Here, we spoke with representatives from three of those companies— Lyle Meyer, global product manager, Industrial Drives, Eaton Hydraulics; Lou Lambruschi, marketing services and e-business manager, Parker’s Electromechanical and Drives Div.; and Craig Nelson, marketing manager, Drives, Siemens Industry U.S.—to learn how VSDs can change the way hydraulics function in an industrial setting.

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drives than other technologies?

Meyer: There are three advantages variable speed pump drives offer the market— low noise, longer life and higher efficiency. Depending on what a particular customer’s needs are, lowimpact noise could be a primary reason to incorporate a VSD into a machine. Eaton’s pumps are capable of running down to zero rotations per minute, so reduced noise in the overall system—and better overall sound quality—are significant features.

Efficiency is a key driver that brought about Eaton’s VSD solution, and there are several market influencers that have led to innovative hydraulic pump and system level technologies—government regulations and energy costs. Energy costs continue to increase over time, and government regulations are continuing to require fewer emissions, both of which have led machine builders to consider more efficient electric motor solutions. If hydraulic pumps cannot operate in the speed ranges needed to complement the wider speed ranges of VSD motors, they can be replaced by electro-mechanical options.

Nelson: I always want to jump to the energy savings because that sort of relates to the biggest cost right off, and that’s the payback. Average time for payback is about three to four years on a retrofit. On a new machine, it’s a lot quicker, anywhere between two and five years.

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There’s another part about it, too, which is environmental ... as well as being “green” on the cost is the environmental impact of being less likely to have hydraulic leaks around your plant. That’s something that everybody really has to keep a big check on because of its environmental impact.

Lambruschi: The biggest advantage tends to be energy savings. Other types of pumps will see increased controllability, quieter operation and potentially longer life.

Drives equipped with fieldbus communications allow for local or remote monitoring of the pumping process, allowing access to parameters like pump loading, running time and energy consumption.

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Q.

The NFPA study said that more people are thinking they would adopt this technology in the next three years versus now. What is holding people back?

Nelson: It’s one of those things where you say, here’s a technology that’s better than what existed and what we’ve had in the past. You just expect it to take off just because it was better. It’s just been a little bit slower for people to adopt it.

There is such an installed base of hydraulics out there. I think most of the new machine users are not even giving it a second thought of going with the new technology. What’s been slower is driving people to retrofit out their existing working system for something that’s better, more efficient, takes up less room, less oil, less

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noise, and all the other advantages that it provides.

Meyer: Generally, there are three things that are holding people back from adopting VSD technology—perception, cost and system design. Perception is now the main issue preventing customers from adopting VSD technology, whereas the number one issue in the past was overall cost. Machine builders initially thought a VSD solution for a hydraulic system was extremely expensive. Today, it is equally cost-effective to make a system hydraulic variable speed as it is to make it electric. Hydraulic components don’t change, and electrical components have experienced much lower costs in the past five years. Fixedspeed starters used to be the lower cost, but now VSDs are generally the same or lower cost as fixed speed.

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Combining Eaton’s PVM and DG1-FR1 solutions offers users up to 70% energy savings, reduced noise and cooling needs and pump downsizing.

Another perception issue is in the certainty of what a VSD system can handle. Machine owners and operators who have not used VSD solutions may not understand that performance will not change, but machines will last longer and cost less. The industry is facing an uphill battle for OEMs to convince customers to adopt VSD technologies into their systems, with a common view of, “what I’ve used in the past will continue to work.” When regulations for electric motor efficiency come into effect in the U.S., VSD solutions will likely be adopted in more applications.

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Q. How do you balance the cost concerns with the efficiency benefits?

Lambruschi: In many retrofit applications with known operating cycles, an estimated payback period can be calculated. In actual applications, this has been shown to be less than 12 months. Cost concerns can also be offset by the fact that many power utilities offer rebates or incentives for the purchase of VSDs for pumping applications. Also notable is the fact that cost savings are not just achieved by efficiency, but by less obvious factors such as reduced maintenance costs and enhanced pump life.

Meyer: Duty cycle is key to balancing cost with efficiency. Pumps are capable of multiple speeds, including zero speeds that allow operators to incorporate VFDs—the building block for smart machine architecture. Before you can start designing machine control, you need components that can handle that level of control. If there are cost increases with a VSD, then they must be paid back on the duty cycle.

At Eaton, customers frequently ask how the VSD system compares to a fixed-speed system from a cost perspective, and the answer is the same. It is led by duty cycle. There are some applications with duty cycles that may not reap the benefits of a VSD system, 2 • 2015

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so we work with customers to review their required duty cycles and help determine which solution is the best for their overall operation.

Nelson: When you look at U.S. manufacturers, they are trying to compete on the global market. We’ve always had the quality and now it’s really keeping the cost in check. Moving to automation and making the machines more cost-effective or more efficient is key for the U.S. manufacturing industry. People need to really look at that and say, okay, I need to look at longer-term sustainability than three to five years.

And you need to realize, it’s still about efficiency and going green. If you look at it, even the larger companies, the larger plants, they’re still looking at ways to

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reduce their energy consumption. This fits well when you have those initiatives. It can offer huge savings. Even though the cost doesn’t start from day one, you start seeing that energy savings from day one.

Q. What markets and regions do you see are driving your growth?

Lambruschi: Within pumping applications, we see particularly good growth in the use of drives on hydraulic power units, replacing proportional valves and similar technologies with a more efficient approach. Growth is seen in multiple regions globally, with concentrations in areas where new production facilities are being built or older ones modernized.

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Nelson: I’d say the industries that have the quicker payback are injection molding and presses, in general. Throughout a number of different types of industries, it’s typically where you’re going to see the lower payback periods that are the first ones that are going to adopt.

Meyer: VSD is growing in popularity in both the American and European markets.

Europe has efficiency regulations in place that are driving machine builders to adopt VSD technology, and these regulations are now starting to be adopted in the U.S. At the moment, European machine designers are required to design to a higher standard, so U.S. designers are looking at this too. As mentioned earlier, energy cost is another big driver. The more energy consumed, the more energy costs—and the greater the emissions—so it’s cost efficient to reduce emissions, particularly on large machinery.

Q. Finally, how is your variable speed

Parker’s AC30 family of VSDs offers high levels of control. Featuring a modular construction, it enables a wide range of communications and I/O modules to be easily added.

pump drive different from others on the market?

Nelson: For us, it’s all about ease of use. We offer this solution with our standard sizes and software. We use the same components that we use for most of our typical servo systems, not just our servopumps, like our Sinamics S120 drives, 1FK7 motors and 1PH8 motors.

The ease of use starts from the beginning when you actually have to size up the system just by using those standard products and having a standard sizing software.

Then we go into the commissioning phase of it. With our standard products, the S120 and the Simotics line, what we have is a combined package that really makes the servo aspect of it plug-and-play.

Lambruschi: Pre-programmed pump application macros and pump-specific parameters, as well as environmental features like conformal coated PC boards, make Parker drives more user-friendly and suited to the tough environments that

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pumping applications are often a part of. Larger drives used on higher power pumps are constructed with field replaceable power modules, allowing for quick and easy maintenance and minimal downtime in the event of failure. Parker is also uniquely positioned to be a complete system provider, being a manufacturer of pumps, hydraulics, and fluid handling components in addition to VSDs.

Meyer: Eaton’s biggest differentiator is low speed—our pump products have been tested down to zero speed. Eaton’s pump products are capable of operating at speeds that are as low as or lower than competitive offerings.

In the past, Eaton pumps or competitive offerings could simply be turned off; however, that function added some complexity to the circuitry.

A pump capable of running at zero rpm takes a lot of complexity out of the circuit, in terms of holding pressure. Eaton’s zero-speed capability decreases system complexity and further enables the machine designer to flexibly design the system.

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COMPONENT FOCUS

Ken Korane • Contributing Editor

How does an

O-ring seal?

O

Images courtesy of Apple Rubber Products Inc.

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O-rings are probably the most common fluid power seals.

They’re made by the billions by manufacturers all around the world, and they prevent leaks in everything from pumps and valves to cylinders and connectors. The compact, economical components handle both static and dynamic operations in pneumatic and hydraulic applications.

These simple seals consist of a donut-shaped ring (technically a toroid) with a circular cross section. They’re typically made of elastomers like Buna N, Neoprene or silicone, but they also come in plastics, like PTFE, metals and other materials. Sizes range from fractions of an inch in diameter to several meters across.

O-rings seal by mechanical deformation that creates a barrier to a fluid’s potential leak path between two closely mated surfaces. O-rings are typically installed in a groove that’s machined or molded in one of the surfaces to be sealed.

Their rubber-like properties let the devices compensate for dimensional variations in the mating parts.

When properly sized, the clearance between the surfaces is less the OD of the O-ring. Thus, as the two surfaces contact, forming a gland, they compress the O-ring, which deforms the round cross section. This diametrically squeezes the seal, and the resulting force ensures surface contact with the inner and outer walls of the gland.

With little or no pressure, the natural resiliency of the elastomer compound provides the seal and keeps fluid from passing by. Increasing the squeeze (say, by using a larger diameter O-ring in the same-size groove) increases deformation and sealing force. But that can lead to problems in higherpressure dynamic applications.

Applying fluid pressure pushes the O-ring against the groove wall on the low-pressure side, increasing the sealing force. Interference between the seal and mating surfaces lets

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the O-ring continue to operate leak-free.

At higher pressures, the O-ring deforms to a somewhat “D” shape, and contact area between elastomer and gland surfaces may double from initial zero-pressure conditions. Due to the elastomer’s resiliency, releasing pressure lets the O-ring return to its original shape, ready for the next pressure cycle. It also lets properly designed O-rings seal in both directions.

Extreme pressures, however, can force elastomer material into the small clearance between the mating surfaces just beyond the groove. Ultimately, the O-ring material shears and flows into the so-called extrusion gap, and the seal fails.

Dynamic applications can hasten seal extrusion. But even in static applications, high pressure can stretch assembly bolts

and open the extrusion gap sufficiently to permit leakage.

While O-rings are relatively straightforward seals, there are still a number of design considerations when specifying them.

For starters, they come in a wide range of materials and countless compounds and variations. Matching the material to the application, however, lets them provide excellent fluid compatibility, withstand various operating environments and handle temperature extremes. Other considerations

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include static versus dynamic (rotary or axial) conditions, operating pressure and whether the system sees pressure spikes. These, in turn, let engineers specify design parameters like proper gland dimensions, gland surface finishes, seal cross-section diameter, material hardness, initial compression, clearance gaps, and even how much the seal expands or contracts in relation to its mating surfaces as temperatures change. Properly designed, O-rings provide long, trouble-free life in countless applications.

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PRODUCT WORLD

Rectangular suction cup Piab piab.com The rectangular DURAFLEX RB20x40P suction cup is suitable for handling small rectangular packages. With a material that features the elasticity of rubber and wear resistance of polyurethane, the suction cups are particularly suitable for handling uneven and porous surfaces. Designed with a single bellows, the 20-Ă—-40-cm cup has a low overall height, making it easy to fit into space-restricted areas, and is available with two alterantive fittings.

Dry-break quick disconnect Beswick Engineering beswick.com The ultra-miniature M3 threaded dry-break quick disconnect is manufactured from corrosion-resistant stainless steel and is rated to 500 psig when connected. Buna-N is the standard seal material; Viton and EPDM are optional and can handle many types of fluids. The advanced dry-break design ensures that there is essentially no leakage during connection or disconnection. It also

Hydraulic power units

minimizes the dead volume between the internal and external ends.

Bosch Rexroth boschrexroth-us.com GoPak HPUs are versatile, with a compact footprint to help conserve valuable plant floor space without sacrificing serviceability. They target a broad power range, from 1 to 75 hp, hydraulic pressures up to 4,000 psi, flows up to 61 gpm and fluid reservoir sizes from 5 to 200 gal. This makes

Solenoidoperated valve

them well-suited for applications including machine tools, plastics extrusion and molding, automotive

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production, material handling and metallurgy. They can be configured with the GoDesigner tool, which streamlines customization for fixed

The DTDB is a low-leakage solenoid-operated

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For further information about products on these pages visit the Fluid Power World website @ www.fluidpowerworld.com

Compact modular valves AutomationDirect automationdirect.com The 24-Vdc compact modular valves are available with 3-way/2position, 5-way/2-position and 5-way/3-position configurations with single or double normally-open or normally-open/normally-closed solenoids. Valves are offered with a 3⁄8-in. push-to-connect tubing input and output sizes of 5⁄32 to 3⁄8 in. NITRA compact modular valves have various mounting positions and require no additional fittings; available accessories include 25-pin female D-sub connectors, blank marking tags, pigtail cables, 35-mm DIN rail mounting brackets and pneumatic release tools.

Directional control valve

Steering solution

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Featuring high-grade iron

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for all applications.

The V080 is designed for a maximum flow capacity of 30 gpm and a max pressure of 5,075 psi. With a maximum flow capacity of 55 gpm and a max pressure of 5,440 psi, the V130 is a mid-size option. The V250 allows for higher flow rates; it is designed for a maximum flow capacity of 75 gpm and a max pressure of 4,000 psi.

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AD INDEX Kocsis Technologies, Inc. ..................34 Lillbacka USA, Inc. ...........................35 Main Manufacturing Products, Inc. ... 4 Master Pneumatics ..........................16 Muncie Powers Products ................... 5 NOSHOK, Inc. ...................................23 O+P SrL ...............................................9 Peninsular Cylinder ..........................12 PHD Inc. ............................................31 Prince Manufacturing Corp .............21 ROSS Controls ..................................33 Servo Kinetics ...................................25 Smalley Steel Ring Company.............. 3 Super Swivels ..................................... 2 Tompkins Industries ..................... IFC,4 Veljan Hydrair Limited.......................13 Webtec .............................................46 Yates Industries .................................. 7

Anchor Fluid Power ..........................37 AutomationDirect .............................. 1 Brennan Industries ...........................51 CD Industrial Group .........................53 Clippard Instrument Laboratory, Inc. ............................BC CS Hyde Company ............................26 FABCO-AIR, Inc. ...............................15 FASTER, Inc. ......................................27 Flaretite, Inc. ....................................50 Flow Ezy Filters, Inc. .........................55 FluiDyne Fluid Power .......................11 Holmbury, Inc. .................................IBC Hunger Hydraulics ............................52 Hy-Pro Filtration ...............................45 Hyde Tools, Inc. ................................23 Hydraulex Global ..............................17 Hydraulic Training Associates ..........57

New twist on pneumatic muscles p.32

From the basic to advanced: selecting directional control valves p.38

Industrial variable speed drives p.48

February 2016

www.fluidpowerworld.com

More efficient

mobile hydraulic

troubleshooting PAGE 42

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