FLUID POWER WORLD HANDBOOK 2023 by WTWH Media LLC

JULY 2023

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2023

FLUID POWER HANDBOOK

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Fluid power overview

Hydraulics overview

Cylinders

Filters

Filtration systems & fluid conditioning

Fittings & flanges

Fluids

Hydraulic hose & tubing

Hose couplings

Hydraulic power units

Hydraulic motion controllers

Motors

Pumps

Seals

Sensing technologies

Hydraulic valves

Pneumatics overview

Pneumatic actuators

FRLs

Pneumatic hose & tubing

Vacuum components

Pneumatic valves

Accumulators

Miniature fluid power controls

Shock absorbers

Ad index

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F LUID POWER OVERVIE W

Staying relevant through times of change Welcome to the 12th edition of the Fluid Power Handbook. This year, we’ve rewritten several articles, including those on hydraulic hose, fittings and couplings, hydraulic motors, and more. We've also added new technical sidebars with frequently asked questions, sizing, and specification tips in every category as we are continually growing our library of basics content for our readership. Fluid power systems are comprised of components that include pumps, cylinders, valves, hose, fittings, gauges, sensors, filters, seals, and reservoirs. Some components are considered absolute necessities, while others are optional and used to refine the system for more precise operation or to increase the lifespan of the system or its individual parts. Throughout this handbook, we detail many of the more widely used components, explaining their operation, their place in the system, and how they should be specified.

While fluid power can be used in almost any industry or application, it is commonly seen in markets that include off-highway, mining, packaging, offshore/marine, material handling, construction, aerospace, automation, and robotics. As we work to keep our fingers on the pulse of fluid power technology trends, we strive to bring our audience the most up-to-date content in the industry. This is also why you will see a deeper focus on electrification this year, as we bring a series of Fundamentals Fridays webinars to life starting in the fall, and we'll take deeper dives into mobile electrification, whether in systems that are fully electric, hybrid or traditional diesel-powered. Additionally, keep reading this issue and our websites for key troubleshooting, maintenance and repair advice from some of the industry's finest. Enjoy this year's read! FPW

Mary C. Gannon • Editor-in -Chief mgannon@wtwhmedia.com On Twitter @FPW_marygannon

SENSORS FOR MOBILE AUTOMATION STRONG – SAFE – EFFICIENT  Position sensors for stroke measurement in hydraulic cylinders  Compact safety rotary encoders for position and speed measurement  Dynamically compensated inclination sensors for precise angle measurement

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F LUID POWER HANDBOOK

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Hydraulic technology overview Hydraulic technology has been helping people work for thousands of years in its various forms. Early use of water to power our world saw the discovery of the watermill, using the hydrodynamic properties of water to turn a water wheel. Water-powered technology offers methods to increase our capacity to process anything from flour or paper by grinding raw materials such as wheat or wood respectively. This early hydraulic technology paved the way for our development and use of fluid power technology as we know it today. Today’s hydraulic systems continue to permeate our daily lives, and even despite widespread electrification, fluid power technology has only increased. However, hydraulics offers an advantage not replicated with any other technology, and that advantage is power density. No other source of motivation creates as much force in such a small space as hydraulics does. Modern hydraulics run 3,000 psi all day, with more powerful systems approaching 6,000 psi or more. With such energy compressed into relatively small spaces, hydraulics offers a level of force not possible with any other technology. Hydraulic machinery powers the construction equipment used to build roads and cities while providing the motivation to plant and cultivate most of the farmland in the world. If you can think of a machine that moves while achieving useful work, it’s likely powered by hydraulics. To exploit hydraulics does not require a machine to operate on tracks or use closed-loop drive systems like much of the mobile machine industry. In fact, simple machines and objects use hydraulics to perform myriad tasks for various industries. For example, the machine tool industry uses small hydraulic power units to operate the clamp or chuck on CNC mills and lathes, while any large aircraft counts on hydraulics to operate its primary flight functions. Even the simple bottle jack used to lift your car to install new wheels takes advantage of the high power of compressed liquid. Hydraulics and pneumatics are both subsets of fluid power, but hydraulics differs from pneumatics in that the former uses liquid to transmit force. At the same time, the latter conveys force using compressed air. Suppliers may manufacture hydraulic fluid from base stocks of mineral oil, synthetic oil or even water-glycol solutions. The most 6

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common fluid in hydraulics is anti-wear oil derived from crude, while premium blends come from completely synthetic base stocks such as polyol esters. For applications requiring fire resistance, fluids must not be capable of supporting flame; otherwise, a hose may mimic a flame flower should it spring a leak in the presence of extreme heat. Therefore, such fluids usually have a water base, like high-water-based fluids or the aforementioned water glycol. Naysayers may argue that hydraulics is dirty, loud, or environmentally unfriendly. However, that lazy argument doesn’t ring true for fluid power engineers. Those claims merely indicate that the described systems are improperly designed, installed or maintained. Combining electric and electronic technologies with hydraulics compliments a machine in many ways. Efficiency increases while maintaining power density, and the sophisticated electronic controls systems pair well in the control of electric-proportional valves, especially when paired with sophisticated transducers. Understanding the operation of and parameters for the application is critical, as is good working knowledge of sealing and contamination control technologies. Even the practice of adding a new component to your system may introduce contamination. Contamination destroys hydraulic components more frequently than any other cause, so you must put fluid conditioning technology at the front end of your machine design. Failure and downtime will plague your machine without the appropriate filters and coolers to keep hydraulic fluid within its ideal operating condition. The bottom line is that intelligent engineering and mindful maintenance will avoid problems in the future.

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HYDRAULIC CYLINDERS

Cylin de Co u r w i t h c u rtesy sh of R A i o n i n g . M In d u st ries

Hydraulic cylinders Few things represent a ﬂuid power

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

disassemble and repair in the ﬁeld. Welded cylinders employ a steel barrel with a cap welded to the bottom and the end treatment subsequently welded to the cap. The rod and piston assembly then has to be assembled around the head — which uses a buttress thread for strength — and is tightened into the barrel. Finally, the single-acting ram is typically just a rod inside a barrel with a single port and requires either a spring or mass to retract. For all cylinders, the critical measurements include stroke length and bore and rod diameter. Stroke lengths vary from less than an inch to several feet or more, depending on the requirement of the machine. Bore diameters can range from 1 in. up to more than 24 in., and piston rod diameters range from 1-2 in. to more than 20 in. In practice, however, the choice of stroke, bore and rod dimensions may be limited by environmental or design conditions.

Cylinder types The three most common types of cylinders are tie-rod, welded and ram, the latter of which is single acting, meaning it is powered in one direction only. Tie-rod cylinders can be single acting, although they are most often powered in both directions. They have machined, square caps and heads being forced together against the barrel by high-tensile steel tie rods fastened by nuts, making them easy to

Cylinder mounting methods Mounting methods also play an important role in a cylinder’s performance. Generally, ﬁxed mounts on the centerline of the cylinder are best for straight line force transfer, ideal column loading and avoiding excessive wear. Pivoting mounts, such as clevis or trunnion, require care in application, because of their capacity to move as the cylinder is stroked, resulting in a possible bent rod or excessive wear.

system the way a hydraulic cylinder does. These true workhorses operate in industrial and mobile applications. When compared with pneumatic, mechanical or electric systems, hydraulics can be simpler, more durable and also oﬀer greater power density. For example, a hydraulic cylinder has about ten times the power density of an electric linear actuator of similar size.

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Tie-rod cylinder. Courtesy of Yates Industries

7 • 2023

FLUID POWER WORLD

COFFEE or TEA? Testing cylinder. Courtesy of Hunger Hydraulics

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Flange mounts — Strong and rigid, but have little tolerance for misalignment. It is recommended to use cap end mounts for thrust loads and rod end mounts for loads under tension. Side-mounted cylinders — Easy to install and service, but the mounts can sometimes create a bending moment as the cylinder applies force to a load, increasing wear and tear. To avoid this, specify a stroke at least as long as the bore size for side mount cylinders (heavy loading tends to make short stroke, large bore cylinders unstable). Side mounts, such as side lugs, need to be well aligned and the load supported and guided.

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Centerline lug mounts — Absorb forces on the centerline, but require dowel pins to secure the lugs to prevent movement at higher pressures or as a result of shock loads. Pivot mounts — Absorb force on the cylinder centerline and let the cylinder change alignment in one plane. Common types include clevises, trunnion mounts and spherical bearings. Because these mounts allow a cylinder to pivot, they should be used with rod-end attachments that also pivot. Pivoting mounts are required for many applications, such as booms and buckets, but are also most prone to rod buckling, especially as the rod reaches end of stroke.

What is the maximum pressure for the application?

Float

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Common types of mounting include:

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The hydraulic cylinder must be rated to work within the pressure limit of the hydraulic system it is installed on. An excavator, for example, can operate at 4,000 psi or more, so light-duty snap-ring cylinders rated for 2,000 psi should be avoided. Cylinders are designed with safety factors of 2:1 to 4:1, so sometimes running slightly over-limit might be acceptable, but not double. 10

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HYDRAULIC CYLINDERS What stroke length will be required?

Ensure that the machine has appropriate clearance, because the longer retracted length of the cylinder should be factored. Also, if stroke is too long, additional support will be required, such as a guided load or stop tube.

What mounting method is being used?

Flange mounting is often best because the load is transferred along the centerline of the cylinder. Non-centerline mounting calls for additional support to avoid misalignment, but these are required when the mechanism must pivot through an arc, so load calculations must be factored accurately. Push or pull or both? Any cylinder can be used as single acting, which is powered in one direction only, but it can only push or pull. When a cylinder pushes, protection against rod buckling and bending must be ensured, which can be achieved through oversized rod material or with a stop tube to prevent full extension, taking advantage of the piston’s load-bearing effect. When a cylinder pulls, there is little concern for buckling, but you should ensure your force calculations factored in the smaller rod side of the piston, which experiences reduced force compared to the cap side. A double acting cylinder is powered in both directions to push and pull.

What push or pull tonnage is required? Always assume peak loads will require additional strength. The rule of thumb is to choose a cylinder with a tonnage rating of 20% more than required for the load; however, this is always applicationspecific, so it’s best to consult a hydraulic professional before you make tonnage assumptions. Cylinder force (lb) is equal to the area of the piston (in.3) times pressure (psi), or F=AxP. Key specifications: Operating conditions — Cylinders must meet the requirements of the design specification, such as force, maximum pressure and mounting configuration, but consideration for operating conditions must also be heeded. Cylinders must also withstand extreme temperatures, humidity and even salt water for marine hydraulic systems. Also, when ambient temperatures rise to more than 300° F, standard Buna-N nitrile rubber seals may fail and will instead require synthetic rubber seals, such as Viton. When in doubt, err on the safe side and choose a cylinder design capable of more of than you will ask of it.

Fluid type — Most hydraulic systems use a form of mineral oil, but applications using toxic synthetic fluids — such as phosphate esters — require Viton seals, which will not break down or swell in the fluid. Once again, Buna-N seals may not be adequate to handle

RAM Industries Inc www.ramindustries.com

F LUID POWER HANDBOOK some synthetic hydraulic fluid, although the gentler synthetics, such as PAO-based stock, will be fine. Hydraulic systems using high water-based fluids may require stainless-steel construction, as well as PTFE (Teflon) seals, especially if no glycol is used in the fluid.

Seals — Seals are the most vulnerable component of a hydraulic system. Properly applied seals can reduce friction and wear, lengthening service life, but incorrect types can lead to downtime and maintenance

W W W. MO B I L E H Y DR AU L I CT I P S. CO M

headaches as a result of failures. Every manufacturer likes to use a diﬀerent style, so it is important to replace them with a similar type and material when rebuilding.

Cylinder materials — The type of metal used for cylinder head, cap and bearing can make a big diﬀerence in performance and reliability. Most cylinders use bronze for rod bearings and medium-grade carbon steel for heads and bases. But stronger materials, such as 65-45-12 ductile iron

for rod bearings, can provide a sizable performance advantage for tough industrial tasks. The type of piston rod material can be important in wet or high-humidity environments (like marine hydraulics) where stainless steel may be more durable than the standard case-hardened carbon steel with chrome plating used for most piston rods. A new option for rod surface treatment is nitriding, which is an oxidation process to increase the surface hardness of metals and corrosion resistance. FPW

What is the best cylinder piston seal? How long is a piece of string? So what? Did you think you’d get a straight answer on a subject like “what is the best cylinder piston seal?” There is no best piston seal, just like there is no best car (it’s the Mazda Miata, by the way). If you’re in the snow belt with five kids, your best car is a seven-passenger with all-wheel drive. If you’re retired in Phoenix, well, then your only option is a Miata. Clearly, what works well in a material handling air cylinder will not provide the best solution for the hot strip mill. That little air cylinder kicking boxes off the conveyor in the Amazon warehouse requires quick, snappy action with low friction seals. The mill cylinder used on the hot strip mill needs high-temperature seals appropriate for high water-based fluids. To continue with these examples, consider that a small air cylinder requires low friction seals to move quickly and does not bother with high-pressure provisions. Buna nitrile O-rings work well in air cylinder pistons but tend towards high static friction, requiring some breakaway pressure to start moving. Upgrading to buna nitrile U-cup seals provides a faster breakaway with no velocity penalty. O-rings are press fit, so are under compression during installation, which causes high static friction. Offering less dynamic friction, the O-ring moves smoothly inside the piston bore until “break away” occurs. Light-duty air cylinders get by with 12

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a single O-ring, but heavy-duty air and hydraulic applications require backup rings to prevent seal extrusion. The backup ring is hard plastic and offers a shoulder to lean on, as it were. A double-acting cylinder will see a backup ring on either side of the O-ring, so support is offered in both directions. Modern designs employ a T-shaped seal with grooves allowing the backup rings to snap in tightly. T-seals have excellent high-pressure capacity, yet even hydraulic applications still experience static friction. Pressure holding capacity is one area T-seals shine, offering little to no leakage in applications where load holding is paramount, such as man lifts. The lip seal offers a pocket where the pressure applied increases the sealing effort by pushing the lip outward to the barrel wall. These are unidirectional seals, so any pressure applied to the heel side of the seal will easily pass fluid. Lips seals such as the U-cup offer less static friction and an easier

breakaway, so applications with oscillations make them the top choice. (Relatively) new technologies, such as crown seals, offer a step up to highpressure seals replacing O-rings and T-seals. A polyurethane seal encapsulates a buna nitrile energizer to create an assembly with less static friction yet tremendous pressureholding capacity. Manufacturers offer many variations on the crown seal design, differing in shape and compound. Using a PTFE seal with a rubber energizer, for example, offers a very high-velocity option that sacrifices leakage somewhat. The moral of the story is that no one seal is the best across all applications. You must understand your application requirements and run with the best seal to suit your needs. You might be surprised that for ultimate high-speed cylinders with potential for side-load, a wide piston with three or four cast iron rings offers the highest speed (but with extreme leakage). Sometimes the best seal is none at all.

Co u

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W W W. S E A L I NG A N D CON TA M I N AT I ON T I P S. CO M

Hydraulic filters much particle contamination in the fluid medium. In fact, some estimate that 75% of all fluid power failures can be attributed to contamination-related issues. Thus you, as an engineer, technician or end-user, who ignores filtration does so at the peril of your hydraulic system. There are multiple reasons why your hydraulic fluid becomes contaminated. Every hydraulic machine is first manufactured with built-in contamination during machining, cutting, welding and grinding of the reservoir and fixed plumbing. Additionally, contamination ingression also occurs from either new oil (which is dirtier than you imagine) or external sources such as fallout, grime, mud, and dust. Finally, the components in your system generate their own particles when friction components such as bearings, pistons, spools and swashplates rub together. Removing all forms of particle contamination is your highest priority to ensure a long, reliable life for your hydraulic machine. Filters are your first line of defense to reduce the number of particles in your fluid. Filters also prevent excessive internally-generated contamination, considering particles exacerbate the rate Hydraulic filter. Courtesy of Ohio of internally generated contamination, Fabricators Co. acting like liquid sandpaper. There are several types of filters for you to choose, the most popular of which are inline cartridge and spin-on filter assemblies. The inline cartridge filter assembly is popular and is available for pressure and return lines. These assemblies have a drop filter cartridge that can be removed and replaced when they become clogged. Spin-on filter assemblies are also used for inline applications, although their location is typically limited to return lines. Some manufacturers make heavy-duty assemblies, rated for upwards of 500 psi, which make them ideal for you to use in return lines experiencing pressure spikes. Other filter options exist, such as bag filters and suction strainers. Bag filters are used when large volumes of fluid are being processed, such as is required in steel mills. They are less common in a “live” system where they’re exposed to primary pump flow but are instead 14

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more popular in high volume kidney loop “offline” systems (see Hydraulic Filtration Systems article to follow to learn more). Also fairly common are suction strainers installed in the reservoir’s pump outlet port. They’re often made from woven steel fibers and are designed to remove larger chunks of contamination that could harm a pump. Care must be taken to ensure your suction strainer doesn’t impact pump inlet conditions, as excessive flow resistance increases the likelihood of pump cavitation and resulting damage. Filter construction is also important when you choose your assembly. Construction dictates not only where your filter can and should be located, but also the flow and pressure rating of the assembly. Material construction ranges from plastic or aluminum for lowpressure (500 psi or less) inline or return line assemblies. For medium pressure locations (1,000-3,000 psi), aluminum or steel housings are required. High-pressure filter assemblies (those rated higher than 3,000 psi) require steel construction for both their filter head and bowl, and are often installed with elements constructed for higher collapse pressure. Construction design of a filter assembly varies with its installed location, and differs based on where in the circuit you locate the filter. Any filter installed in a working pressure line requires the capacity to survive that pressure, and then some for safe measure. Return line filters are generally only required to handle backpressure related to flow, which increases due to flow intensification and also to pressure differential created from the clogged element itself. Filters are sized appropriately to handle the maximum flow possible with reasonably low backpressure. Filter assemblies are installed with bypass valves that open when backpressure reaches a predetermined level. The backpressure is created as the element becomes clogged with particles. As the bypass valve opens, fluid sidesteps the element itself, flowing around it to avoid excessive and damaging backpressure, especially in return lines. As a bonus, larger filter assemblies have higher dirt holding capacity, which itself is a critical design consideration. Once you arrive at a filter assembly suitable to your application’s installation requirements, have selected the appropriate pressure rating, and then sized it appropriately to reduce backpressure, you can continue by considering how finely you want to filter your fluid. Every filter manufacturer of reasonable reputation tests

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Optimicron filter element. Courtesy of Hydac

Many fluid power systems fail simply because there is too

FILTERS - HYDRAULIC & LUBE OIL

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Features and Benefits • Patented insertion ring for filter head flange mounting prevents leakage • Patented integrated baffle wall creates settling zone for returning oil (degassing) with simultaneous cooling effect • Tank is optimized for air and heat removal • Tested for leakage (no end-user testing is required) • Tank is certified clean, eliminating time-consuming flushing processes and testing • Lightweight and cost efficient • No risk of corrosion

• Available in four (4) performance optimized sizes (7, 12, 18, & 25 gal.) • Return-line filter options available with Quality Protected aftermarket retaining elements

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Mobile applications have unique requirements for hydraulic components. Often, these components need to be small, compact and as lightweight as possible. Making sure these reservoirs are secure is often overlooked. HYDAC’s Plastic Tank (TNK) Reservoir, a money and time-saving solution also includes mounting straps in three configurations for all 4 sizes!

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Why should you use return filters in your hydraulic system? The venerable return filter is just as crucial to your hydraulic system as your kidneys are to your body. Could your hydraulic system survive with no return line filter? Sure, I suppose in the same way you could survive without kidneys if you strapped on the dialysis machine for five hours a day a few times a week. The hydraulic equivalent to the dialysis machine is the (no pun intended) kidney loop filter, which runs continuously to trap even the finest particles. However, such machines are much more expensive than simple return filters.

TT95R series PowerGuard return line filter element. Courtesy of Todd Technologies Inc – TTI

You’ll find that return line filters are the least expensive option, coming in at a fraction of the investment as pressure filters or the aforementioned kidney loop filters (also known as offline filtration). There are return filters for every budget, ranging from spin-on filters actually found on Amazon to premium in-tank units with ultra-fine synthetic elements. You install return filters in the return line of your hydraulic circuit, appropriately enough. Return filters offer many advantages. First, they offer you the best combination of cost and performance, although I strongly recommend you consider options better than what’s available on Amazon. Spin-on filter assemblies are pretty common, but just as with everything, not all filtration is made equally. You owe your expensive hydraulic machine the filtration quality it deserves, so I recommend only synthetic fiber medium. Synthetic fibers, such as glass fiber, offer the best combination of low micron filter efficiency, low pressure drop and high dirt holding capacity. In addition, the depth media style elements used in high-efficiency filters trap particles throughout the entirety of the media rather than clog the top surface of the media like inferior paper elements. In-tank style filter assemblies provide a convenient mounting location that also avoids messy drips from changing spin-on filter elements. The in-tank assembly drops into a hole on the reservoir lid, leaving only the return line port outside the tank. The lid removes to expose a pull-out filter element, which is easily lifted out and avoids the inevitable dripping that occurs when a spin-on element is removed. In some circumstances, elevated sections of your hydraulic machine may drain its fluid out of your return line when your filter is removed, so be sure to change them quickly. Luckily with in-tank assemblies, the return fluid drains directly down the tube and into the reservoir with no mess. Manufacturers also offer their best filter media with in-tank return line filters. Expect to see filter elements capable of β3 > 1000, should you require it. Here, we describe a 3-micron filter and its beta ratio of 1000. The beta ratio describes how many particles were measured upstream of the tested filter and compares that to the number tested after — higher ratios are superior. Stick to filter elements with at least 200 β Ratio for your given micron size. A β3 > 1000 is about as good as it gets. But in some cases, filtration this fine might be too good. Finer filtration creates more pressure drop as smaller clearances less easily pass fluid. The assembly must be sized for the filtration quality chosen for return line filters. Because return line fluid velocity should remain low, it’s too risky to simply change your filter element to a lower micron version without understanding its effect on pressure drop. Flow surges will create pressure spikes, which could cause your machine to run erratically or even damage some components. Other than cost and real estate, there is no downside to oversized filters — mainly because they also offer superior dirt-holding capacity. 16

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Pressure filters. Courtesy of MP Filtri

and then publishes its filtration ratings, expressing the lowest micron size the filter will efficiently remove, and what that efficiency rating is. You hear filters referred to as their micron rating, such as 5 micron. Anyone can throw a rating at a filter and call it a day, but how you qualify that number dictates how effective the filter is at removing particles of the rated size. Manufacturers must express the beta ratio measured at the given particle rating size for the rating to mean anything. The beta ratio expresses the difference between particles measured before a filter and then after the filter. The higher the ratio, the higher number of particles were trapped in just one pass through filter on a dedicated test rig with special test dust. For example, a beta ratio of 200 represents that for every 200 particles entering upstream of the filter only one particle makes it through. Just as you must specify beta ratio with micron rating, so too must you specify micron rating with beta ratio; they are arbitrary without each other. Written properly, it may read β5 ≥ 200, which means the filter is rated for 5 microns, greater than or equal to beta 200. Once the beta ratio is known, some simple math converts that number to an efficiency rating. Simply take the beta ratio, subtract one, and then divide by the beta ratio. For example, (200-1)/200 = 0.995, or 99.5% efficiency. The previous example tells us our hydraulic filter removes particles of 5 microns and larger at an efficiency of at least 99.5% in a single pass. Always look for the highest beta ratio you can find. FPW

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Filtration systems and fluid conditioning When ultimate filtration is required, an offline system is most efficient. Offline filtration requires a dedicated pump and motor to circulate tank flow through an often very fine filter with high dirt holding capacity. Often called a “kidney loop” filter, these systems run even when the machine does not, and are not exposed to unstable operating conditions related to the primary circuit. The downside is the added expense of an additional pump, motor and filter assembly. You can increase filtration effectiveness with an offline filter system. Offline filtration uses a dedicated lower pressure pump (still often a hydraulic pump), which draws fluid from

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

A filter cart with very fine micron rating will clean your hydraulic system and help remove fine particles not trapped by the machine’s permanently installed filters. Offline filtration also enables changing of filter elements while the machine is running, as shutting down the kidney loop has no association with machine operation. Some filtration systems employ duplex filters, which are two filter assemblies installed in parallel, separated by a three-way ball valve. This design allows for live selection of either filter so the other can be replaced. Most filter manufacturers offer a filter system dedicated to the offline filtration market that is highly efficient and offers high dirt holding capacity. Offline filtration is typically the highest quality in a manufacturer’s product line, which is reflected in the cost of these products. To help justify the purchase of such a system, they are often sold as portable, small units that can be carried by a handle, or large units requiring a wheeled cart to manage their bulk. These units can be wheeled from machine to machine, where a suction tube is placed into a port of the reservoir and then passes through its own filters before being injected back into the tank. Depending on the size of the tank, the filter system’s flow rate and filter quality, one might leave the filter system running on the machine for hours or perhaps days.

Permanently mounted offline systems are now more commonly used as well. They are often mounted to a panel, either near the reservoir or directly attached to it. Eliminating intermittent filtration of the portable type ensures that fluid is clean from storage to service. Some of these filter systems are installed with auxiliary electronics, such as particle counters. A particle counter will give you a live reading of the ISO Code of the oil passing through the unit, so you can leave the unit running until the desired code is achieved. If this type of system seems out of your reach, note that some hydraulic distributors will rent these machines out for a reasonable cost. Removing water in hydraulic fluid Water does your hydraulic system no good. It reduces lubricity, increases corrosion and increases oxidation. Free water settles to the bottom of a reservoir and gets trapped by specialty filter elements or other equipment. However, saturated water is more difficult to remove because it is essentially humidity inside the oil. The amount of water held in saturation depends partly on temperature and pressure. Hotter oil under pressure easily holds more water in saturation, but the problem occurs when the oil cools again, and free water releases itself from the oil. Free water does the most damage, so awareness of your system’s

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OFCO-F

HYDRAULIC FILTRATION SYSTEMS AND F LUID CONDITIONING condition and the tendency of its water to condense might change how you approach your treatment of the problem. If ambient conditions encourage perennial water contamination, a vacuum dehydrator offers one of the best solutions to prevent humidity from condensing into free water. Water’s boiling point varies with pressure, so automotive cooling systems are pressurized to allow the coolant temperature to rise well above the boiling point at sea level. Conversely, water under a vacuum boils more readily (fun fact: water in the presence of a near-complete vacuum will boil at freezing temperatures). The relationship between pressure and boiling allows fluid power designers to remove saturated water by first heating the oil and then exposing it to a vacuum. The moderate heat (110-160° F less), when applied to 20 in.-Hg or less, easily boils the water out of the oil while the vacuum pump carries it away. Sure, you could boil the water out at 212°F, but you’d expose the oil to irreversible oxidation damage. Instead, the vacuum dehydrator offers

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a safe and effective method to lower dissolved water to less than 10% and remove free water entirely. The vacuum dehydrator looks much like a sophisticated filter cart, and is often portable. It works much like an offline filter, where you insert a suction hose into your reservoir while you run the fluid through the machine and back into the tank with dry oil. A single machine will support many power units but could also dedicate itself to a single problematic machine. A vacuum dehydrator doesn’t have to operate on live machinery and may also dry out stored oil in drums or tanks before filling a power unit. In fact, there’s no reason a dehydrator couldn’t be combined with highefficiency filtration to provide your hydraulic machine with the cleanest, driest fluid every time you need to top of the tank.

VUD vacuum dehydrator. Courtesy of Hy-Pro Filtration

FPW

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Hydraulic fittings & flanges Improper selection or improper use of hoses, tubing, fittings, and assemblies can result in machine failures, leaks, personal injury, or even property damage if the failure is catastrophic. Understanding your plumbing standard chosen for your hydraulic system, and following the generally accepted installation standards reduces the chance of failure and prevents productivity-sapping machine downtime. Engineers, designers, and technicians looking to specify plumbing for fluid power systems need to consider a few things besides correct size. You need to consider if the hose end fittings will be reused or permanent? What fitting standard will be on the machine? What hose was chosen or required for the machine. Hydraulic hose ends are offered in two styles: permanent and reusable (also known as field attachable ends). Permanent hose ends are crimped on using special machinery, and the “teeth” within the housing and stem clamp hard on those hose, preventing removal through any method this side of a saw blade. Reusable hose ends require the technician to first install the ferrule, SAE flange connectors. Courtesy of Main Manufacturing

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JIC fittings. Courtesy of Tompkins

which uses a left-handed thread that bites down on the hose’s cover. The technician then installs the socket, which threads traditionally but into the female threads on the outer end of the ferrule. Because the two thread opposite directions, tightening of the socket does not loosen the ferrule — in fact, the assembly just gets tighter. There is a limitation to the pressure holding capacity of reusable hose ends, but they’re suitable for average working pressures. They’re installed using a vice to clamp the ferrule while a requisite wrench or socket wrench torques the socket home. No special equipment is required next to simple hand tools, although an impact wrench or air ratchet makes for quick work. Crimped hose ends are permanent because the ferrule is deformed as the crimping tool crushes it to the manufacturers specified outside diameter. The teeth in the ferrule clamp into the hose’s cover right down to the reinforcement. Sometimes swaging is required using specialized equipment, which is the process of removing the outer carcass, although the practice is more often seen as redundant and obsolete. There are three common types of coupling interfaces used in hydraulics www.fluidpowerworld.com

today: thread interface, mated angle, and O-ring. Each design has its own method of sealing, each vastly different, and some better than others. Threaded couplings have two constructions of thread: male (outside threads) and female (inside threads). The National Pipe Tapered thread, as the name implies, is manufactured with a tapered thread angle. When the male and female components are threaded and torqued together, the tapered threads apply pressure upon one another and deform- the flanks to create a seal. Mated angle couplings form a seal when the male and female threads are screwed together and the seat and face are compressed. Two types of mated angle seals are SAE 45° and JIC 37°, although there are other standards. In the hydraulic realm, the JIC standard is the most popular because of its easy to install and reliable nature. Fittings with angled seats for sealing have straight (parallel) threads. The threads themselves do not seal fluids as with tapered threads. Instead, the threads function to mechanically bring the two mating angle seats together through the mechanical advantage of the thread. National Pipe Straight Thread Mechanical Joint (NPSM) brings two 30°

HYDRAULIC FITTINGS & F L ANGES

tapered seats together to make the seal while employing the NPT thread. SAE 45° flare couplings are used on lower pressure applications, such as fuel lines, hot oil lines or refrigerant lines, but are rare in hydraulics. JIC 37° angle seats are used on medium-pressure and high-pressure lines on heavy equipment to join hydraulic hose assemblies to hydraulic system components. O-ring designs are the pinnacle of high-pressure sealing, and there are three common types of O-ring seal designs — O-ring boss, flat-face, and O-ring flange. In the boss design, straight threads torque the fitting into the port and encapsulates the O-ring inside of the machined groove. With the flat face fitting, the O-ring resides within a machined groove on the male’s face, and the compression of the threads provides a positive seal between the connection. The solid male O-ring face seal fitting will mate only with a swivel female O-ring face seal fitting.

O-ring flanges such as the SAE Code 61 and Code 62 style make highpressure, large-diameter connections. A port is bored with a center outlet, and is surrounded by a smooth, flat face for the seal to interface, and uses four tapped holes to fix the four mounting bolts tight onto flange clamps. There are no threads on this coupling besides the four bolt holes, while the flange itself has the groove for the O-ring to reside and seal. When specifying a hydraulic hose end, you must consider the following criteria: • • • • • • • •

Hose diameter Crimped or ﬁeld-serviceable ends Type of ﬁtting end and standard, such as female JIC or male ORB Solid or swivel end Straight or angled end Maximum temperature Maximum pressure Skive or no-skive FPW

Elbow tube fitting. Courtesy of Brennan

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How do you install metric fittings? There are no secrets here, but installing metric hydraulic ﬁttings depends on the type of ﬁtting being used. You will need several tools to install them. Generally, you will need various wrenches, a hose cutter (if you’re making metric hose assemblies), a deburring tool, and, in some cases,

machinery requiring hydraulic fittings or plumbing, aside from metric combination wrenches, much of what you use will perfectly suit the needs of metric fitting installation. To install a metric hydraulic hose end fitting, follow these steps just as you would with SAE hose assemblies: 1.

thread sealant. If you create hydraulic hoses with metric ﬁttings, you also need a hydraulic crimper, just as with

any other hose assembly. If your shop already manufactures or supplies hydraulic ﬁttings and adaptors, it’s likely you already carry an appropriate accoutrement to arm you for the task of metric ﬁtting installation. And if you manufacture

Cut the hydraulic hose to the appropriate length using a hydraulic hose cutter employing a steel blade. Use a deburring tool to remove any burrs or rough edges from the cut end of the hose. Look up the hose insertion length in the manufacturer’s literature, and mark the hose at the speciﬁed distance. Then, insert the ﬁtting into the hose’s end, ensuring the insertion depth matches the mark location.

Here are some tips for installing metric hydraulic ﬁttings: 1.

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5. 6.

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Use the correct size and type of fitting for the application while also confirming that the thread form you’ve chosen is correct. In rare circumstances, competing thread standards will actually fit together but offer poor fitment and leakage protection. Use the correct hand tools for the job. Metric fittings have metric hex nuts, so choose the appropriate metric wrench for the job. For adapters, metric sockets also work well. Adjustable wrenches can work, but be careful because the opportunity to strip the nut increases, especially with older, worn wrenches. Tighten the fitting only until it is snug, do not overtighten. Over-tightening may damage or strip the threads or even damage the seal. Perform a pressure test after installation to ensure the fitting is properly sealed and secure.

Nobody is perfect, so expect that mistakes can occur. Here are some common mistakes to avoid when installing metric hydraulic ﬁttings: 1.

Use MAIN Manufacturing Products, Inc.

Crimp the fitting onto the hose using a hydraulic crimper or hydraulic press and then measure the crimp OD to confirm it is within the manufacturer’s listed specification.

Using the wrong size or type of fitting for the application. Cutting the hydraulic hose at an angle or with a dull blade. Over-tightening the fitting, which can damage the threads or cause the fitting to crack. Failing to use a thread sealant for tapered threads or using the wrong type of sealant. Conversely, using thread sealant on straight threads or those designed for O-rings. Skipping the pressure test after installation. Omitting to purchase or install O-rings where required.

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Hydraulic fluids and their benefits All hydraulic fluid is designed to transmit fluid power energy through a system, and for the most part, they do the job the same way. But that doesn’t mean all oil is the same. In fact, there are five common types of hydraulic fluid, each with benefits and downsides, whose use depends on the application best suited for them. Anti-wear hydraulic fluid enjoys the comfortable throne atop the hydraulic fluid kingdom. Anti-wear oil derives from petroleum oil, offering excellent lubricity, superior corrosion protection, and great oxidation resistance. AW oil generally offers a good viscosity index and heat transfer as well but fairs poorly in flame-resistant applications, being quite flammable. AW oil is the jack of all trades product that suits the majority of hydraulic systems and machinery in a wide range of temperature applications. Additives easily improve the base oil to increase performance, and AW oil is offered in a wide range of viscosity offerings. Biodegradable hydraulic fluid gets its base stock from renewable and natural oil sources, such as seed sources like soy or canola. Biodegradability defines the capacity of a material to eventually break down into elemental components in the presence of microorganisms. If the base material is something bacteria like to eat, the material will likely break down into water, C02 and some minerals over time. These fluids benefit not only from their renewable source but their safer impact on the local environment should they spill or leak. Bio oils also offer excellent lubricity and corrosion protection, but their viscosity is more likely to change with temperature. Granted, the overall effective temperature range of most bio-oil is very good. Bio-oil makes its home in any hydraulic application where the possibility of contamination exists in a sensitive environment. Forestry machinery does well to be offered with bio-oil, which does not contaminate soil after a leak. Food-safe applications take advantage of the fully ingestible nature of bio-oil since crosscontamination results in a less daunting cleanup effort after a spill.

A subset of biodegradable oils are Environmentally Acceptable Lubricants or EALs, which are typically used on machinery operating on or around waterways, where the impact of hazardous and toxic oil is most severe. Many environmental regulations require fluids to be EAL compliant, such as the 2013 VGP, a US regulation to prevent the discharge of toxic lubricants into US waterways. An EAL hydraulic fluid must meet three primary criteria — they must be biodegradable, not bioaccumulative, and offer low toxicity. In addition, each additive to the fluid must also meet those three criteria, such as viscosity improvers, anti-wear chemicals, or detergents. Synthetic fluid offers good performance across the board in most categories — viscosity index, lubricity, oxidative stability, corrosion protection and thermal transfer capacity. Depending on the base oil, it may also offer fair fire resistance. With a quality additive package, a synthetic blend offers the best choice for most hydraulic fluid requirements. Expect to have excellent all-weather performance, superior lubrication and corrosion protection. Phosphate ester was created as a synthetic form of fireresistant fluid, used primarily in steel mills or aircraft hydraulics. If your hose springs a leak, the last thing you need is a flame thrower should a spark intercept the jet of oil. Phosphate ester also enjoys good overall oxidative stability, corrosion protection, and thermal transfer properties. However, its viscosity tends to be more affected by temperature than other fluids. Water glycol offers some excellent properties as a hydraulic fluid; mainly being water, it has an outstanding viscosity index, fire resistance, and thermal transfer capacity. However, as you would imagine, it’s merely okay regarding lubricity and oxidation while being the poorest of the top five with corrosion resistance. Water glycol has replaced phosphate ester in many steel mill applications, being a much less aggressive fluid on seals, paint, and personnel. However, it tends to be a high maintenance fluid, requiring frequent testing to confirm its specific gravity suits specification. Typically, the ratio is 60:40 or 65:35 glycol to water, and it is often dyed pink or red for identification purposes. Finally, as you can imagine, the water evaporates over time and requires replenishing. FPW

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HYDRAULIC HOSE

Tera-Glide braided hydraulic hose assemblies. Courtesy of Texcel

Hydraulic hose You find hydraulic hose on countless industrial and mobile hydraulic machines. It provides designers with a familiar and sensible method to route hydraulic fluid to and from reservoirs, pumps, valves, motors, and accessories. Hose flexibility makes it the primary choice for hydraulic functions that rotate or pivot, for remotely operated systems such as underwater robots, or where ultimate flexibility reigns king, such as a cable carrier. Applications where noise and vibration make for an unpleasant work environment may sometimes be improved by installing hoses in place of pipes or tubes. A tube more easily resonates and vibrates to transmit noise, and the synthetic rubber tube and cover of a hydraulic hose dampen vibrations. Hydraulic pumps, especially, sometimes generate an ear-piercing sound as pressure waves’ ripples exit into the flow path. Using a hydraulic hose with a synthetic or textile reinforcement provides superior resistance to reverberations and noise.

Hose construction Hydraulic hose construction typically utilizes three primary layers — the inner tube, the reinforcement, and the outer cover. The inner tube must suit the machine’s hydraulic fluid and not just the particular chemical composition of that fluid. The temperature must also play a part in your selection since high-temperature applications may require a plastic tube such as Teflon. In contrast, standard hydraulic hoses work well with synthetic rubber, like buna nitrile. The reinforcement layer provides most of the pressure capacity for which hydraulic hose is known. They range from six spiral wires of high-strength steel for high-pressure hose down to textile braids for low pressure, non-conductive applications (non-conductive hose resists electrical conductance). The most common reinforcement method uses two layers of braided steel to offer excellent flexibility alongside respectable pressure capacity. The reinforcement also provides a structural element. A suction hose, for example, requires resistance to vacuum rather than positive pressure. A metal coil spiralled through the hose combined with www.fluidpowerworld.com

a suction-resistant inner tube is the most common structure of suction hose. “Truck hose” falls into spiral coil camp and offers a common and practical choice for pump inlet hoses for even the highest flow applications. The outer cover holds the dual role of keeping the construction held fast while offering protection from external chemical and physical damage. Abrasion commonly wears the cover away and subsequently exposes the reinforcement, leading to potential failure. Expect to see neoprene or special nitrile polymers used on the cover to help resist abrasion and chemical attacks. In addition, the cover material plays a role in resisting ambient heat, so select your hydraulic hose with a holistic approach. Special hose types Specialty hydraulic hose may offer a solution to the problem you didn’t know your application had. Anti-static construction prevents the buildup of electrical charge, which is paramount for explosion-proof applications in mines, refineries, and oil & gas industries. However, sometimes ambient conditions threaten a hydraulic hose’s performance and lifespan. Although the 7 • 2023

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inner tube maximum temperature rating considers the hydraulic fluid temperature, the outer cover must resist extreme heat conditions like those in steel mills. If heat isn’t enough menace to hydraulic hose assemblies, conditional threats also include UV light, ozone, saltwater, and chemicals. In extreme examples of each, manufacturers offer solutions to resist the degradation of the outer cover and the subsequent possibility of premature failure. Thoughtful consideration of your environment, whether at sea or in a chemical processing plant, will surely sidestep any potential pitfalls.

Ultra-high pressure hydraulic hoses. Courtesy of Spir-Star

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Selection tips When selecting hydraulic hose construction, consider flow rate (which dictates hose sizes), temperature, fluid type, max pressure, and ambient conditions. Armed with the previously discussed fluid and ambient condition understanding, hydraulic hose must meet the performance criteria dictated by the system’s pressure and flow. High flow applications require a large diameter hose, which in turn reduces the pressure resisting capacity of the hose, in most cases. Only a few construction types,

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such as 100R13, offer both high pressure and large diameter solutions. However, with high-performance hose comes drawbacks, such as the double threat of stiffness and weight. Most hoses are manufactured to SAE J517, European Norm (EN) or ISO Standards. In North America, you will primarily come across the SAE J517 Standard and its common nomenclature 100RXX, where the XX ranges from numbers 1 through 19 throughout the series. Each standard, such as the iconic 100R2 or 100R12, offers detail on construction and application. Unfortunately, older hose design experiences the unfortunate symptom of segmented applications — a side effect often requires the designer or technician to choose multiple hose construction types for a single machine. One recent trend in hydraulic hose technology is to create a single standard for most common sizes that offers the best of many worlds, such as with 100R17 hose — offering 3,000 psi working pressure for every size from 1/8 to 1 in. while exhibiting excellent flexibility across the range. Although no hose offers a solution for every possible application, consider your options carefully when selecting the best hose for your machine. FPW

HYDRAULIC HOSE

Hydraulic Live Swivels Inline & 90°

What impacts hydraulic hose life?

Courtesy of Adobe Stock

Hydraulic hoses are critical components of any hydraulic system, and their lifespan is essential for the system’s efficiency and longevity. Several factors impact hydraulic hose life, from environmental conditions to maintenance practices. If you heed the tips below, you can enjoy long life from your hoses. One of the most critical factors impacting hydraulic hose life is temperature. High temperatures can cause hoses to degrade, crack and break down quickly, leading to leaks and system failure. Conversely, extremely low temperatures make the hose brittle and more prone to cracking. When your hose experiences both extremes frequently, repeated expansion and contraction may rapidly degrade your hose assembly. Another important factor is high pressure, which can cause hydraulic hoses to swell, leading to loss of flexibility and, eventually, failure. Similarly, pressure spikes caused by fluid hammer can damage the hoses by fatiguing the reinforcement or even shearing it catastrophically. The type of fluid used in the hydraulic system also impacts hose life, as fluids, such as phosphate ester, are more corrosive than others, which can cause the hose’s inner tube to deteriorate over time. Incompatible fluids may also cause the hoses to swell and lose their mechanical properties, leading to leaks and failure. The environment in which the hydraulic system operates is another crucial factor, and exposure to sunlight, ozone, and other elements causes the hose to fail sooner than desired. Similarly, exposure to chemicals, oil, and industrial fallout can also lead to hose failure should the outer carcass of the hose lack compatibility with those chemicals. Proper maintenance practices are also essential for extending hydraulic hose life. Regular inspection of hoses for signs of wear and damage, especially from abrasion or at the crimp joint, can help detect issues early and prevent failure. Proper routing and clamping of hoses can also help prevent damage from abrasion and flexing. You must also choose the correct hose for the job, which is critical for extending its lifespan. Different types of hoses are designed to handle different pressure and temperature ranges, as well as different types of fluids. For example, using a large-diameter 1-wire braised hose in an application better suited for 4-wire spiral wound reinforcement is a recipe for disaster. Know your hoses and their limitations. In addition to these factors, the hydraulic system’s design can impact hose life. Properly designed systems will have adequate hose lengths and precise routing to prevent excessive hose bending, twisting, or stretching. Hydraulic hose is manufactured to bend relatively well, but highpressure hose tends to be stiffer. Attempting to bend ultra-stiff hose will result in fatigue, so be sure to choose high-flex hose for those applications. Reinforcement layers dislike torque, so avoid excessive twist during installation. Several factors impact hydraulic hose life, including temperature, pressure, fluid type, environment, maintenance practices, hose design, and system design. Regular inspection and maintenance, proper hose selection, and system design are essential for extending hose life and ensuring hydraulic system efficiency and longevity.

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HYDRAULIC COUPLINGS

What are hydraulic couplers? Hydraulic quick couplers are indispensable tools in various industries that rely on hydraulic systems. They play a crucial role in connecting and disconnecting hydraulic hoses and attachments swiftly and efficiently. These couplers provide a secure and leak-free connection, allowing for seamless fluid transfer in hydraulic systems. Typically made of durable materials like steel or brass, hydraulic quick couplers consist of two mating halves: a male and a female coupler. The male coupler features a protruding nipple with a check valve to prevent leakage when disconnected. The female coupler has a corresponding socket with internal seals and locking mechanisms. When the two halves are brought together, they form a tight seal that prevents hydraulic fluid from escaping. Also called quick-connects or quick disconnects, these fittings allow fluid to flow when the male and female sides are locked together. Conversely, when disconnected, the quick couplings prevent fluid leakage using check valves to block exiting fluid. One of the primary advantages of hydraulic quick couplers is their ability to connect and disconnect hydraulic components rapidly, saving valuable time during equipment setup or maintenance. They eliminate the need for time-consuming and messy manual threading or wrenching. With a simple push or pull action, the couplers

securely lock into place, ensuring a reliable connection. Moreover, hydraulic quick couplers enhance safety by minimizing the risk of fluid spills and leaks. The design of the couplers prevents accidental disconnection during operation, reducing the likelihood of injuries and damage to equipment. The two most common types are the agricultural (pioneer) and flat face. The agricultural coupler uses two check balls that open to allow oil flow when pushed against each other when the couplers are connected. The flat face couplers use flat poppets that push inside one another, and offer superior contamination resistance, as the agricultural type can trap dirt. The threaded coupler is a third, less common option for specialty applications, such as trucking and high-pressure work tools. They employ male threads on the nipple portion, and when inserted and tightened into the female coupler, squeeze together to open both check valves. Thread-to-connect couplers offer a very high-pressure rating while offering very little flow in return. Quick couplings should be sized based on their flow capacity. It’s a mistake to size couplings relative to the thread size on the hose or fitting to which the coupling attaches. For example, 3/8 in. quick couplings may only flow 4 gpm at 20 psi of backpressure, while the hose itself may flow double that amount. It’s perfectly okay to use bushings to reduce the larger thread on the coupler down to the size of your plumbing. If your hose thread is larger than your coupling thread, your coupling is likely undersized. Flat face couplers offer a

more significant flow path with reduced pressure drop. Their interlocking sleeves open an extensive cross-section than poppet-style couplings. The poppets or ball-checks of the latter interfere with the flow path, creating pressure drop. Just like many (but not all) hydraulic components, you get what you pay for. A set of ballcheck couplings purchased from a local tractor parts store will offer little in common with the premium flat face couplers. Inexpensive couplings will corrode more quickly, which is a problem with mobile applications. As previously mentioned, the flow rate will suffer using ball-check couplings, forcing you to oversize the set and pay more regardless. Cheap couplings will also leak more readily, all the while offering little in the way of smooth connection and disconnection. Finally, the poppet style loses oil every time you disconnect it and is also prone to collecting contamination in the female end’s open face. Premium flat face couplings offer corrosion-resistant parts that are precision-machined to offer the smoothest, most reliable connection. As

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MC series (multi-coupler). Courtesy of Holmbury

discussed, their large flow path offers lower pressure drop, so you benefit from using a more appropriately sized set. Finally, most flat face couplings offer a twist lock that prevents accidental disconnection should an object hit the sleeve. Multiplate couplers let users simultaneously connect and disconnect multiple hydraulic lines that contain residual pressure. This reduces operator error and improves KPIs (key performance indicators), saving companies time and money in the field. FPW

FSC series (Flat-Face Screw Connect). Courtesy of Holmbury

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Hydraulic power units Nearly every single hydraulic system shares one thing in common — they’re run by a hydraulic power unit. Although some units are multitaskers, like the engine on a tractor, most often they’re purpose built for the single task of converting mechanical energy into hydraulic energy. The scope of a power unit ranges from fractional horsepower electric units to monstrous constructions in the hundreds of horsepower. The power unit exists to supply the machine with hydraulic energy in the form of pressure and flow, without which you have idle components. You must first calculate the pressure and flow required by the actuators in the systems. You may calculate this step more than once as you balance performance with economy, as

very few machinery OEMs have no limits, financial or otherwise. After you arrive at your pressure and flow requirements, you specify the pump type and size. Pump cost and complexity are vast but this dictates the level of performance you can expect to achieve with your actuators. The type of pump used correlates with the direction you must take with reservoir design, filtration and complexity of pumping. A gear pump, for example, requires only suction and pressure lines. A load sensing piston pump, conversely, will add to that a case drain line and one or more hookups for the load sense network. The rest of the power unit can be built around the pump. You must choose the size of your reservoir. Although opinions vary, you can’t go wrong with sizing it as large as possible. Limitations will exist for cost and footprint, but on average, expect to need at

L-shapred HPU. Courtesy of Dakota Fluid Power

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least three times pump flow at minimum, to ideally five times if it can be achieved. Every multiple of pump flow provides a precious extra minute of fluid dwell time. Reservoir size is critical for many reasons. A large volume of hydraulic fluid relative to pump size gives time for fluid to cool before being drawn back into the circuit where heat soaks in once again. Large tank volume means large tank surface area, and in addition to the first point, this large surface provides a radiation layer to improve cooling. Additionally, with more fluid, particles settle more effectively than if they immediately re-enter the circuit, as with smaller tanks. Opposite to the settling of particles, air bubbles are given more time to rise, reducing the potential for cavitationrelated damage from aeration. After you calculate tank volume, you must now consider the reservoir construction type. Reservoir style plays an important role in ensuring the pump inlet conditions are ideal, preventing conditions favorable to cavitation. Economics are also primary here, ranging from the vertical type at the low end, to the L-shaped at the upper end. The former is compact but difficult to service, while the latter is highly serviceable but large and expensive. Highly complex hydraulic systems consist of many components — some related to the function of the circuits, like manifolds, directional valves and pressure valves — and other components required for fluid conditioning and monitoring. Filters, heat exchangers, and pressure gauges are components added to ensure safe and reliable power unit operation. To ensure ease and convenience, as many components as possible should mount to the reservoir. As such, these components command much real estate, and reservoirs are oversized to accommodate. Use your hydraulic schematic as the first step in the power unit creation process. A hand-drawn schematic helps you choose actuators and major components, but a detailed drawing helps with the visualization

HYDRAULIC POWER UNITS

What are compact hydraulic power units? Hydraulic power units are both the source of hydraulic energy and fluid conditioning. The hydraulic reservoir provides a mounting surface for the hydraulic pump and its prime mover while offering up real estate to mount filters, coolers, valves, and accessories. In addition, the reservoir stores the hydraulic fluid, providing a surface to radiate heat while evacuating air. Hydraulic power units range from those as large as shipping containers to some as small as a bread box. The compact hydraulic power unit packs a lot of punch into a small package, including most of the critical components within reason. The motor, pump, valve head, breather cap, and valves pack themselves into one convenient and economical package. Most compact power unit manufacturers offer standard designs for common machineries, such as auto shop hoists, dump trailers, snow plow attachments, bin tippers, forklifts, lift tables, dock levellers, and power tailgates, just to name a few. What you’ll notice in common with these applications is their low-duty cycle applications, where their functions are used infrequently, slowly or both. It’s common for these units to come with dc motors with 12 or 24 V and 120 or 220 Vac units with no more than a few horsepower. Their modular design allows a designer to select

the pump size, electric motor, reservoir type and size, and end head that each suits their application. The end head is a combination component that provides the reservoir, pump, and motor mounting point. The end also includes cavities and circuitry to install valves to create simple hydraulic circuits. Most compact power unit manufacturers offer a D03 valve pad option atop the end. Just as with industrial stack valves, simple hydraulic circuits are easy to create or modify. In addition, modular mounting pads allow installation of more valves in series or parallel, which is as simple as a few longer tie-rods to hold the valve pads together. Most units come installed with relief valves, often just a ball and spring design. In addition, a check valve installed after the pump prevents loads from dropping when the motor shuts off. This basic configuration is typical to nearly every compact power unit design and would make for the most economical. Reservoirs tend to be small,

ranging from a quart up to 5 gal or so. The size depends less on cooling and contamination settling and more on satisfying differential cylinder volume. You may have to choose between a vertical and horizontal style reservoir, each offering slightly different advantages. The vertical reservoir needs its breather cap to be close to the end head yet with a long suction tube to reach down to the bottom of the reservoir. Meanwhile, the horizontal style makes do with a short suction tube and flexibility with its breather cap location. The pumps used in compact hydraulic power units are almost exclusively gear pumps, and they are close-coupled directly to the end head and use a small metal splined drive coupler or sometimes a tang shaft. Displacement options range from small to downright tiny. It’s not unheard of to see 0.25 cc/rev of displacement or less. Because of limited horsepower on most power units, high-pressure systems must make do with a minimal flow rating.

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Compact hydraulic power units may not be your best option for high duty cycle applications. Still, if you usually use traditional hydraulic power units, you’ll be surprised by the economic advantage these units oﬀer. Even if you require a more complicated circuit, you can simply order one of these units with pump, motor, and reservoir and instead plumb up your own control and conditioning circuit. For example, the pressure port may lead to your own custom valve manifold and then return through the high-quality inline ﬁlter of your choice — your options are endless. This HPU is commonly used for a dump trailer, requiring a power up and power down hydraulic controls and comes standard with a pendant for remote operation. It can be configured with different pump displacements and choice of steel or plastic tanks in various sizes to meet the customer’s needs. Courtesy of Tandy and ALA Industries

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Vertical, portable HPU. Courtesy of Dakota Fluid Power

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of component layout. A circuit drawing should be modified to include every component that will exist on the power unit, not only for the assembly technician to understand how to install and plumb all the components, but for future troubleshooting and repair. Experienced hydraulic designers know what a power unit needs, but seeing the circuit helps spot gaps where less obvious components should be drawn, and then subsequently added to the bill of materials. Test points, ball valves, bellhousings, drive couplers, etc., are all important and should be included. Once a schematic is complete, a bill of materials (BOM) can be created from it. The most important set of components is the pump/motor assembly. It includes the chosen pump, a motor of adequate power capacity, a pump-motor mount, and drive coupler set. The pump/motor mount — often called the bellhousing — rigidly fixes the C-Face electric motor to the pump and provides a gap to install the couplers. A coupler slides on the motor shaft, its mate slides on the pump shaft and then a synthetic rubber insert is placed between them before the couplers are pushed together and fixed in place with set screws. Be sure to select a coupler set rated for the required horsepower and pressure spike potential. Once together, the pump/motor assembly is mounted to the reservoir, preferably with isolation mounts. These mounts are either welded or bolted to the reservoir and consist of two metal plates galvanized onto either side of a chunk of rubber. This isolator prevents excessive pump/motor vibration from resonating through the steel plates of the reservoir; an important requirement because hydraulic power units are already prone to nasty harmonic noise pollution. In succession, the remaining “fixed” components are mounted to the reservoir. Accumulators mount off the side, valve banks to the top, filtration inside or on top, level/temperature indicator located to the side, ball valves www.fluidpowerworld.com

(very important!) hard plumbed to the suction port, and any other component either welded or bolted to the tank are now installed. With all fixed components now complete, you can fabricate the power unit’s plumbing. Most designers prefer tube but it is timelier to fabricate. It is semi-permanent and is more reliable in the long run. Hose can be used for plumbing as well, although hose invariably fails. Hose has its place, however, especially if noise and vibration is a concern. Tube transmits vibrations more readily, but hose can often dampen it. Most frequently, you plumb a power unit using a combination of hose and tube. At the end of fabrication, the unpainted components are removed, and the power unit is cleaned and prepped for paint. Epoxy paint is best because it resists oil and provides a durable finish. When the paint dries, the technician re-assembles the unit, and the final stages of power unit fabrication begin. The electrician now wires the electrical components, and this includes adding any electrical enclosures, transducers, switches, etc. Wiring of the motor itself will often occur on sight at commissioning, but the electrician wires the valves and control boxes when the power unit is manufactured, to allow for testing. Once electrical is complete, the technician fills the tank with oil and jogs the motor from the electrical panel to ensure the motor is turning the correct direction. The technician turns on the pump, checks for leaks, and tests the HPU at pressure. The final step, after successful testing, includes draining the tank, installing on a skid, and wrapping up for shipping. FPW

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How are motion controllers used in fluid power? Motion controllers are used extensively on industrial machinery, but speciﬁc controllers exist that are dedicated for use on electrohydraulic machinery. They provide closed-loop control of electrohydraulic and pneumatic applications from single to multi-axis systems. Common applications can be found in materials, aerospace, forestry, energy, metals, entertainment, and more. Like all motion controllers, these computational devices reduce system error by taking an input command, comparing it to a feedback signal and helping to bring the position or output in line with the input or required position. They ensure precise

pressure and force control while smoothly transitioning from position to force control. This precise and repeatable motion improves productivity by reducing mistakes in manufacturing. Additionally, the multi-axis design of most controllers helps to reduce system design costs by allowing for synchronization, tight control of gearing through system changes, and camming of the gear ratio so the relationship between slave and master axis is expressed as a nonlinear equation. Most motion controllers work in concert with position and pressure transducers and sensors, which send signals from data logging devices to the controllers. They can accept analog voltage or current signals. Additionally, they receive positional signals from encoders and may also output PWM (pulse width modulation)

Case study: motion controllers synchronize lifting cylinders Delta Computer’s Delta RMC150 controllers manage the synchronization of hydraulic arm lifting cylinders at logging mill company Western Forest Products (WFP). In this application, their mill in Ladysmith, B.C., uses two powerful, 31-ft long hydraulic cylinders with a load capacity of 50 tons to lift bundles of hemlock, Douglas ﬁr and red cedar logs out of the adjoining bay.

Delta’s RMC150 can simultaneously control up to eight motion axes.

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The cylinders connect to a pair of lifting arms, which attach to either side of a large cradle. The cradle raises the log bundles in an arc onto the elevated log deck where the mill operates. Both lifting arms must move in unison, or www.fluidpowerworld.com

oﬀ-center forces could damage the cradle, halt production and necessitate costly repairs. To manage the synchronization of the hydraulic arm lifting cylinders, Delta Computer Systems RMC motion controllers have a builtin axis synchronization function, whereby the motion of one axis can be precisely linked electronically to that of another. For this application, Wilson chose the eight-axis RMC150 electrohydraulic motion controller. Synchronized movements The motion controller manages the lifting cylinders using position data obtained from magnetostrictive linear displacement transducers (MLDTs) mounted in smaller 30-in. following cylinders. Each following cylinder mounts on the lifting arm below a main lifting

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MOTION CONTROLLERS

Next level hydraulic control

RMC70 modular, below, and RMC200 controller, right. Courtesy of Delta Motion Control

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signals. In hydraulic designs, using a motion controller that provides analog control signals to drive proportional valves is best. In a hydraulic system, these controllers ensure synchronous motion by controlling a servo or proportional valve. The controller then needs to work with the feedback devices, like encoders or pressure or position transducers, to create command trajectories for the motors to follow. The controller uses this data to create a motion profile to tell the motor where the load should be positioned and when and how fast it must move and when to stop. Finally, easy programming of most motion controllers allows users to simply use built-in commands for complex motion profiles. Using advanced controllers and software allows easy graphical programming of control profiles.

RMC150 Up to 8-Axis

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cylinder. By reading position information from the MLDTs and factoring in the size ratio between the smaller and larger cylinders, the motion controller precisely calculates the required position of the main cylinders. The Delta RMC150 also connects to pressure sensors mounted in the large cylinders that allow the motion controller to monitor the hydraulic pressure and display it on the bundle lift ’s human machine interface (HMI). The RMC150 precisely synchronizes motion operations. When one cylinder moves, the other will as well. If an axis should lag too much, the controller will stop the motion. The log carriage will raise and lower at diﬀerent speeds depending on the load, and the amount of force required to move the bundle lift changes 7 • 2023

depending on the angle of the arms. Though the speed may change, arm motion is continuously synchronized. In addition to the main lifting arms, the Delta motion controller handles a third motion axis that controls a secondary piece of equipment that lifts logs, one at a time, from the log deck onto the belt that feeds into the mill. To control this axis, the RMC150 gets position inputs from an MLDT embedded within another following cylinder, to control oil ﬂow in this cylinder via another hydraulic servovalve. Because one RMC150 can handle up to eight motion axes simultaneously, it was no problem for the same controller to handle the bundle lifting arms and the log lifting arm all moving at the same time.

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Fast, precise, simple and elegant. Use Delta RMC motion controllers and graphical RMCTools software to simplify and improve complex motion. 1-50 axes of synchronized position, velocity and pressure/force control. Visit our website for videos, case studies, and specifications. Find a case study of your industry and application. Discover simple, fast, and precise electro-hydraulic motion at deltamotion.com

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HYDRAULIC MOTORS

Hydraulic motors Hydraulic motors are rotary actuators that convert hydraulic energy into mechanical torque. Using the pressure and flow provided by the hydraulic pump, hydraulic motors rotate to pull, drive or winch external loads on various hydraulic machines spanning construction equipment to food mixers. The three most common constructions of hydraulic motors are the gear, vane and piston varieties, each with a unique style. In addition, some common types use orbital technology, such as gerotor and geroller motors. Manufacturers offer fixeddisplacement pumps in all the major construction types, with only the piston variety available with the variable-displacement option. A fixed displacement means the theoretical motor volume remains constant, while torque and speed vary only by adjusting flow and pressure through various means. A variable-displacement motor modifies displacement through swashplate control, essentially offering infinite adjustment of speed and torque within its range of control. Understand motor torque and speed Torque, or the turning and twisting effort of the force of the motor, is expressed as inchpounds (in.-lb), foot-pounds (ft-lbs) or newton meters (Nm). When describing the torque performance of a hydraulic motor, we describe three different areas. First, breakaway torque is typically used to define the

minimum torque required to start a motor with no load, and this torque factors in internal friction and the pressure required to overcome static friction. Running torque describes the load-induced torque a motor uses to move whatever rotary function the machine requires. Running torque may be relatively stable, such as a winch function, but could also vary widely for dynamically changing conditions, such as wheel drive motors. Starting torque is the minimum torque required to start a motor under load and is a combination of load-induced torque (which factors inertia) and breakaway torque. The ratio of actual torque to theoretical torque provides us with the mechanical efficiency factor of a hydraulic motor. We calculate the hydraulic motor’s internal volume to describe how much fluid the motor circulates in one single rotation, otherwise known as displacement. Displacement is a volume calculation, so units are expressed in cubic centimeters or cubic inches. The larger the motor’s displacement, the higher the force created per pound per square inch of hydraulic pressure, but the motor’s velocity is inversely proportional to displacement. Motors are often described with theoretical numbers because the geometry that makes up the motor’s physical displacement is offset by clearances and leakage that prevent actual torque from matching theoretical torque. So if you wish to achieve a desired output speed (usually described in revolutions per minute or rpm), you must also factor in

A36VM axial piston variable motor, for hydrostatic drivetrains. Courtesy of Bosch Rexroth

efficiency. For example, any given piston motor may achieve 90% efficiency, so that provided with 100 gpm, the motor will waste 10 gpm as pure heat rather than motion. You can calculate motor speed by the following formula, where 231 is just the number of cubic inches in a gallon: Flow in gpm x 231 ÷ cubic inch displacement = rpm Motor type and selection Each motor type enjoys different natural characteristics and expect performance to be relative to cost. Gear motors, for example, are inexpensive but generally limited to medium pressure, medium torque and a narrow range of displacement (although they generally offer the lowest displacement options), and they are often rated for high speed (3,000 rpm or more). On the other hand, vane motors offer the fluid power designer a mediumpressure, medium-speed, quieter, and more efficient option than the gear motor option. The piston motor provides a wide range of capabilities, although counting on few being considered an economical capital

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purchase, their efficient nature quickly provides a long-term return on investment. As small as 5 cc or as large as 1,000 cc or bigger, the piston motor also offers a vast array of control options. You can also expect high pressure, high torque, highspeed options — as well as being the most efficient choice. The construction of each motor, as you’d expect, varies widely by style. Gear motors feature two gears, one driven (by the shaft) and the other idle. Their function is simple; highpressure oil enters the inlet port, which flows around the gears and housing to the outlet port. Although torque is a function of displacement and pressure, providing high pressure at the inlet does not guarantee high force. The pressure differential from the inlet and outlet port matters, so understand that every psi of backpressure reduces effectual output. At the medium-pressure and

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FLUID POWER WORLD

F LUID POWER HANDBOOK cost range, vane motors feature a housing with an eccentric bore. The motor’s vanes slide in and out of its rotor, and displacement is controlled by the size of the vanes and the width of its eccentric bore. The movement of the pressurized fluid causes an unbalanced force, which in turn forces the rotor to turn in one direction. Piston-type motors are available in various styles, including radial, axial, and bent-axis styles, to name the most popular. Radial-piston motors feature pistons arranged perpendicularly to the crankshaft’s axis. As the crankshaft rotates, the pistons reciprocate radially by the fluid pressure. Axial-piston designs feature several pistons (the most common is nine) arranged and reciprocating axially inside a housing (cylinder block, rotor, or barrel). The pistons ride on a wear plate which is either fixed or adjustable, and the thrust plate’s angle partially dictates the pump’s displacement.

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This cylinder block rotates about its axis by a shaft aligned with the pumping pistons. Two designs of axial piston motors exist — swashplate and bent axis types. Swashplate designs feature the pistons and drive shaft in a parallel arrangement. In the bent-axis version, the pistons are arranged at an angle to the main drive shaft. Another advantage to the piston pump is the control options. Electro-proportional control, two-speed control and even automatic displacement control varies torque and speed based on demand. The orbital motors use a special spool or disc valve to automatically distribute pressurized flow to the fluid volume inside a uniquely shaped rotor arrangement. The gerotor design has a simple inside and outer rotor. In contrast,

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Thorx family of cam lobe motors reduces shock at speed changeover by 70%. Courtesy of Danfoss

the geroller design employs rollers to offer lower friction, higher mechanical efficiency, and higher start-up torque than gerotor designs. In addition, they provide smooth, low-speed operation and offer longer life with less wear on the rollers. Gerotors provide continuous fluidtight sealing throughout their smooth operation, although their efficiency is relatively low. There are several essential things to consider when selecting a hydraulic motor. First, you must know the maximum operating pressure, speed, and torque the motor will need to accommodate. This will allow you to calculate its displacement and flow requirements to specify the pump flow and pressure required to operate it. Hydraulic motors can use different fluids, so you must know the system’s requirements. Does it need a bio-based, environmentally-friendly fluid or fireresistant one, for example, which may require special seals or technology? In addition, contamination can be a problem, so knowing its resistance levels is essential so you may choose appropriate filtration. Cost is a huge factor in any component selection, but the initial cost and expected life are just one part of the equation. You must also know the motor’s efficiency rating, as this will determine whether it runs cost-effectively. In addition, a component that is easy to repair and maintain or quickly changed out with other brands will reduce overall system costs. Finally, consider the motor’s size and weight, as this will impact the size and weight of the system or machine with which it is being used. FPW

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Hydraulic pumps Hydraulic pumps are used in literally every single hydraulic power transmission system. A hydraulic pump is the device that converts mechanical energy into hydraulic energy, which is a combination of pressure and flow. A hydraulic pump can be any device that you can input force into to create pressure, which in turn creates flow. Most hydraulic pumps have a mechanical input from an internal combustion engine or electric motor. These prime movers input their mechanical power to the hydraulic pump in a rotational fashion. The input shaft of the pump will be connected to gears, vanes or pistons of the hydraulic pump, where they will rotate or reciprocate to transfer pressure (force) to the hydraulic fluid. As long as the force (pressure)

created by the pump is high enough, flow will occur at a rate dictated by the displacement volume of the pump and the speed at which it rotates. These pumps, also called positive displacement pumps, have a small clearance between rotating and stationary parts. A specific amount of fluid is delivered to the system for each revolution. Positive-displacement pumps can be further divided into two categories: fixed- and variable-displacement. Fixeddisplacement pumps provide a single, specific volume displacement per revolution. In variable-displacement pumps, displacement per cycle can vary from zero to maximum volumetric capacity. Some of the more widely used types of positive-displacement pumps are gear, piston and vane.

GRH gear pump. Courtesy of ALA Industries

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Gear pumps can be either internal or external styles. External gear pumps are one of the most popular types used in modern hydraulic systems. Gear pumps produce flow by using the teeth of two meshing gears to move the fluid. Their simple construction ensures limited purchase costs and servicing. They feature decent mechanical and volumetric efficiency, compact dimensions and low weight/power ratio. Of the three common types of positive displacement pumps, gear pumps are the least efficient; their appeal is low cost and simple design. External gear pumps can be equipped with straight spur (the most common type), helical or herringbone gears. In operation, the drive gear and driven gear rotate, creating a partial vacuum at the pump inlet (where gear teeth unmesh) that draws fluid into gear teeth. Gear teeth mesh at the outlet, forcing fluid out of the pump.

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Internal gear pumps contain one internal and one external gear. They pump fluid in the same manner as external spur gear pumps. In the basic design, the internal gear, which drives the outer gear, has one tooth less than the outer gear. As they mesh, the teeth create sliding seal points. Because their transition zone from low to high pressure (the area over the crescent) is relatively long, internal gear pumps can offer lower noise levels than some other types of pumps. Gears are made of special steel and are often case hardened and quench hardened. Then gears are ground and fine finished. Proper tooth profile design and geometric proportions can reduce pulsation and noise levels during pump operation. Piston pumps supply high flows at high speed. Two types of piston pumps—axial and radial—are manufactured in both fixed- and variabledisplacement versions. Axialpiston pumps contain one or more pistons that convert rotary shaft motion into axial reciprocating motion. An angled

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cam (or wobble plate) rotates, causing pistons to reciprocate and take ﬂuid in as they move toward the thin part of the plate. Fluid is expelled as pistons approach the thick end. In the bent-axis design, both pistons and shaft rotate, making a wobble plate unnecessary. Bent-axis pumps use the drive shaft to rotate pistons. With the longer sealing paths along the piston walls, piston pump eﬃciencies tend to be higher than other types of pumps. In addition, variable-displacement pumps can provide savings by only providing the pumping necessary for the function, saving additional energy and costs.

Radial-piston pumps (fixed-displacement) are used especially for high pressure and relatively small flows. Pressures of up to 10,000 psi are common. Variable-displacement is not possible, but sometimes the pump is designed in such a way that the plungers can be switched off one by one, so that a sort of variable-displacement pump is obtained. Radial-piston pumps are characterized by a radial piston arrangement within a cylinder block. As pistons reciprocate, they convert rotary shaft motion into radial motion. One version has

Avoid this one piston pump mistake Hydraulic pumps are primarily designed to convert incoming prime mover energy into hydraulic energy, manifested as pressure and flow. The term hydrostatic refers to a state of pressure equilibrium, especially in a confined space. All traditional hydraulic applications are hydrostatic, and in most cases, if you shut down the pump, physical loads should hold fast using the already pressurized hydraulic oil. It would be easy if everyone used hydraulic pumps for hydraulic applications, but not everyone seems to like things easy. For example, I can think of a dozen ways to lubricate a CNC machine or large bearing, and even if the lubrication medium was hydraulic fluid, I could think of better pump designs for this application. Still, some spindles require hydrostatic bearing support for very high-speed machining, so

Yuken remote pilot piston pump Courtesy of ALA Industries

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sometimes high-pressure hydraulic fluid is the only solution. You’d be surprised to know how often hydraulic pumps are used for water-based coolant for CNC machines. Although hydrostatic bearings absolutely require high pressure to support the assembly, using them for coolant is a surprising take on the pressure compensated pump. Dynamic pumps use impellers to essentially throw the fluid to create inertial pressure, much like the impeller on a boat. You can cap the outlet port of a dynamic pump just the same as you can a pressure compensated piston pump. I suppose engineers started using pressure compensated pumps for cooling because of their ability to maintain a set pressure even when downstream flow paths wear, such as with orifices inside of tooling. Through-tool coolant will slowly erode the internal diameter of its flow path, which increases the effective orifice size, thereby reducing pressure drop. So long as the pump is oversized for the application, it will maintain the pressure compensation set point despite downstream increases in orifice size (to a point). However, there are right and wrong ways to use hydraulic pumps for lubrication and coolant. For example, variable displacement axial piston pumps are overbuilt for these applications, mainly because they handle thousands more psi than any lubrication or coolant application needs. At the same time, these pumps actually require a minimum operating pressure. Although minimum compensator pressure depends on the make and www.fluidpowerworld.com

construction of the pump, expect minimum pressure of at least 200-300 psi. Unlike gear pumps, for example, the pressure compensated pump has many parts engineered to operate effectively only when pressure exists. For example, the compensator, control piston, and (sometimes) the bias piston run from pilot pressure, but pressure is required to keep the entire pump under tension. In a pump’s rotating group a cylinder block rotates, and the swashplate angle forces the pistons to reciprocate, which in turn pumps fluid. As the piston passes “top dead center” and begins to retract into the block to create pressure, the entire assembly maintains tension until the piston again extends to suck in the fluid. Without pressure, there exists no tension in the rotating group. With no tension, the entire assembly is a floppy collection of metal parts banging and slapping as they reciprocate and rotate at maximum displacement because no hydraulic pressure exists to bring the pump on standby. Hydraulic oil feeds typically down through the hollow pistons where a pinhole in the socket feeds pilot pressure to keep the slippers lubricated against the swashplate, but with no standby pressure, no lubrication occurs. If you are using, or are considering using, a hydraulic pump for your lubrication or coolant application, you must guarantee your pump never drops below its minimum pressure rating. This may occur from orifice wear, but I’ve also seen hydraulic circuits designed to “unload” the pump when coolant isn’t required. You’re better off installing a poppet valve to block outlet flow than to unload the pump because only running with no oil will damage a pump faster.

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cylindrical pistons, while another uses ball-shaped pistons. Another classification refers to porting: Checkvalve radial-piston pumps use a rotating cam to reciprocate pistons; pintle-valve pumps have a rotating cylinder block, and piston heads contact an eccentric stationary reaction ring. Rotary vane pumps (fixed and simple adjustable displacement) generally have higher efficiencies and lower noise levels than gear pumps. They can be used for mid pressures of 2,500 psi. Some types of vane pumps can change the center of the vane body, so that a simple adjustable pump is obtained. These adjustable vane

V20 sin gle va ne pu Co u Fluid P rtesy of FluiDmp. ower yne

pumps are constant pressure or constant power pumps. Displacement is increased until the required pressure or power is reached and subsequently the displacement or swept volume is decreased until equilibrium is reached. A critical element in vane pump design is how the vanes are pushed into contact with the pump housing, and how the vane tips are machined at this very point. Several types of “lip” designs are used, and the main objective is to provide a tight seal between the inside of the housing and the vane, and at the same time to minimize wear and metal-to-metal contact. Forcing the vane out of the rotating center and toward the pump housing is accomplished using springloaded vanes, or more traditionally, vanes loaded hydrodynamically (by the pressurized system ﬂuid). FPW

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Hydraulic seals One of the arguments often used against hydraulic systems is that dreaded word, leakage. But with proper sealing, leakage won’t be a problem with your system. Leakage from the cylinder or across the piston, along with the ingress of unwanted contaminants, can not only decrease the lifespan of the components, but it will affect the efficiency of the entire application. Material options Proper material choices will be determined by the seal’s environment. Different types of chemicals react differently to different fluids, while some materials have higher pressure and temperature limits. They also must be able to withstand extrusion, so materials are very application-specific.

Polyurethane Polyurethane is an organic material whose chemical composition is characterized by a large number of urethane groups. Urethanes belong to the thermoplastic elastomers (TPE) family and close the gap between thermoplastic and elastomeric materials regarding hardness, deforming behavior and consistency. Within certain temperature limits, polyurethane possesses the elastic characteristics of rubber combined with the advantages of a rigid plastic. The composition of the material is determined by three components: polyol, diisocyanate and a chain extender. The type and amount of these materials used, and the reaction conditions, are decisive in determining the properties of the resulting polyurethane material. They possess the following properties: y high mechanical, tensile strength y good abrasion resistance y modulus of elasticity is variable y wide range of hardness values, while retaining good elasticity y good resistance to ozone and oxygen y outstanding resistance to abrasion and tear 48

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Temperature range for use: –30 to 80° C; high performance types (compounds) up to 110° C in mineral oils (long-term exposure temperature).

Acrylonitrile-Butadiene-Rubber (NBR) NBR is a polymer of butadiene and acrylonitrile. The acrylonitrile (ACN) component affects the following properties: y elasticity y cold flexibility y gas permeability y compression set y swelling resistance in mineral oils, greases and fuels An NBR material with low ACN content has very good cold flexibility (down to approximately –45° C) and moderate resistance to oil and fuel. In contrast, a material with very high ACN content with optimum resistance to oil and fuels, may have a cold temperature flexibility only down to –3° C. With rising ACN content, the elasticity and the gas permeability decrease and the compression set becomes worse.

777 double-acting, energized piston seal. Courtesy of Hallite

NBR provides: y good resistance to swelling in aliphatic hydrocarbons; greases; fire retardant hydraulic fluids of Groups HFA, HFB and HFC y good resistance to hot water at temperatures up to 100° C (sanitary fittings), inorganic acids and bases at concentrations, and temperatures which are not too high y high swell in aromatic hydrocarbons, chlorinated hydrocarbons, flame retardant hydraulic fluids of the Group HFD, esters Temperature range for use (depending on the blend composition): –40 to 100° C and for short periods up to 130° C (material hardens at higher temperatures). For special blends, cold flexibility extends down to –55° C.

Fluoro-Rubber (FKM) Copolymers, terpolymers or tetrapolymers with various compositions and with fluorine contents from 65 to 71%, which have varying resistance to surrounding media and varying cold flexibility. www.fluidpowerworld.com

HYDRAULIC SE ALS

What are seal extrusion gaps? For any seal to function well in a fluid power application, it must resist the extreme forces attempting to squeeze the material through even the smallest gap like so much play dough. The gaps available to a seal to squeeze through are called extrusion gaps. To understand the extrusion gap, you must first understand the primary role of a seal, which is to keep separate two areas of differential pressure, fluid or medium. For the sake of this discussion, hydraulic seals keep pressurized hydraulic fluid where it best serves our purpose — somewhere it can transfer energy with as little lost to leakage as possible. Any two separate areas requiring a seal also include a gap where two individual components meet, such as the end-seal on a hydraulic cylinder that seals the tube ID from the air outside the cylinder. An endseal design may be subjected to extrusion as tie rod stretch opens the seal gap. No matter how well-engineered, machined and assembled, no two separate components can be so close to each other as to prevent leakage between those two components at high pressure. Thus, seals literally fill the gap between parts. The gaps in and around the seal cavity also offer a dangerous opportunity. Those gaps offer a path for the seal to take when exposed to pressure of sufficient force. Many soft seal compounds, such as Buna Nitrile, act almost like putty when exposed to extreme pressure. That putty has the opportunity to squeeze through the extrusion gap. Seal manufacturers publish cavity dimensions and tolerances that best suit the seal construction and polymer. It’s essential to design within these published dimensions to prevent the possibility of extrusion. A small enough extrusion gap is no gap at all, making the seal effective against even the most extreme pressure cycles. It simply takes intelligent engineering and precision manufacturing. 7 • 2023

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Sometimes even small extrusion gaps may eventually wear away at seals, especially when movement is involved. For example, a piston seal under high pressure, even with tight gaps, still has potential for extrusion. As pressure softens the seal, the added friction of movement can pull the seal out through the extrusion gap, albeit very slowly. This slow process of extrusion is sometimes referred to as “nibbling.” Image 2 shows an example of a seal extruded over some time. All threats of danger aside, hydraulic component manufacturers are well aware of the potential for seal extrusion. Pumps, valves, and cylinders are all manufactured within tight tolerances of the appropriate dimensions, and extrusion is rare for oﬀ-the-shelf hydraulics. The

concern comes when rookie engineers or designers do not adhere to the catalog speciﬁcations. Be sure to select a seal appropriate for the application and create the seal cavity best suiting that seal.

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An example of extrusion nibbling on a hydraulic seal. Courtesy of Trelleborg

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FKM provides: y tough resistance to high heat y excellent resistance to oil, hydraulic fluid and hydrocarbon solvents y good flame retardance y low permeability to gases y high swell in polar solvents, ketones and fire-retardant hydraulic fluids

elastomeric component to energize a lip seal configuration because of the low elasticity and tendency to cold flow over time.

Newer materials (cross-lined by peroxides) have good resistance to media, which can only be tolerated to a small extent, if at all, by conventional FKM. Temperature range for use: about –20 to 200° C (for short periods to 230° C). Special grades: –50° to 200° C.

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

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

683 low friction rod seal. Courtesy of Hallite

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Six common seal designs Following is a list of some of the most common seal designs used in fluid power applications.

Wipers y provide aggressive wiping force y prevent mud, water, dirt and other contamination from entering y allow lubricating oil film to return to system on inward stroke y protect main sealing elements, thus increasing life of seals y often made from polyurethane, which offers high abrasion resistance y often used as a linkage pin grease seal Rod Seals y prevent system fluid from escaping to atmosphere y must provide sealing function at low and high pressure y require excellent extrusion and wear resistance y should provide good pump-back capability for lubricating oil film y often must withstand up to 6,000 psi Buffer Seals y must withstand high pressure exposure y protect the rod seal against pressure spikes y pressure-relieving capability prevents pressure build-up between seals y increase rod seal life y allow for wider extrusion gaps y require high wear resistance www.fluidpowerworld.com

Wear Bands y prevent contact between metal parts in the cylinder y center rod and piston from housing elements y increase seal life O-rings y used in static applications and radial or axial deformation to maintain sealing contact force y double-acting, so seal on both sides of a component y can be used as energizing elements or as primary seals y self-acting; do not require system pressure or speed to create the seal FPW

SENSING TECHNOLOGIES

Sensing technology Sensors are used heavily in ﬂuid power applications, to measure critical functions such as position, ﬂow, pressure, temperature, and more. The variety of devices that exist to gauge these functions are many, but here, we take an in-depth look at some of the more commonly used devices — position and pressure sensors and transducers.

Pressure transducers, a subset of pressure sensors, can be any number of devices that sample and record the pressure in a system. They convert a pressure measurement into an analog electrical output signal, which can be used by sensing instrumentation such as microprocessors and computers. This is accomplished through physical deformation or mechanical deﬂection. Criteria to consider when selecting a pressure transducer are mechanism type, input and

M9100 pressure transducer. Courtesy TE Connectivity

transducer’s output signal can be used in systems that require digital signals, such as a programmable logic controller (PLC) or a programmable automation controller (PAC). Some pressure transducers output current rather than voltage, and are referred to as transmitters. These values typically fall within tens of thousandths of amps. When choosing the output of a pressure transducer, keep in mind the input requirements of the device that will be accepting the signal, the distance the signal must travel and possible interference that can be found in the environment around the system. FPW

output, and performance specifications. Common types are strain gauge, and thick/ thin film. Strain gauge use the mechanical deformation under pressure of strainsensitive variable resistors, which may be integrated into measurement circuits such as a wheatstone bridge. In a thick/thin film transducer, a titanium nitride or polysilicon film may be applied to sensing equipment to impart the circuit with piezoelectric sensitivity to pressure. Almost all pressure transducers require a source of electrical input. Input voltage can vary but typically falls under 10 V, while output is typically in the hundreds of thousandths of volts. A change in system pressure would cause a change in the transducer’s resistance on the electrical circuit and would result in a change to the output voltage. With the aid of an analog to digital converter (ADC), the

Pressure sensors for hydraulic applications. Courtesy of Sensata

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Positioning sensing Several technologies exist to provide position feedback or data of a cylinder’s position. The sensor converts the position into a proportional analog or digital signal.

Hall-Effect Transducers use a magnet that communicates with the Hall chips, which then give an output to the internally built microprocessor. The output from the microprocessor is converted to a signal required by the user interface such as voltage, current, PWM or digital output. Using Hall-effect technology on linear position sensors allows manufacturers to make small, compact designs that can be mounted internally or externally to a cylinder. Halleffect technology is well suited to mobile applications as it is highly resistive to shock and vibration. It is used commonly on steering and depth applications. LVDTs or Linear Variable-Displacement Transducers are durable and resist shock and vibration while oﬀering high repeatability. These absolute linear position/displacement transducers convert a linear displacement into an analog electrical signal. Their design includes transformer coils wound around nonmagnetic coils.

LVITs — Linear Variable Inductive Transducers — are contactless position sensing devices, with sensing ranges up to 30 in. or more. Most designs feature an inductive probe surrounded by a conductive tube. This is attached to the moving object to make the reading. These contactless position sensing devices use eddy currents developed by an inductor in the surface of a conductive movable element to vary the resonant frequency of an L-C tank circuit. Modern electronics using microprocessors and small component size makes high performance possible, achieving linearity errors of less than ±0.1% and temperature coeﬃcients of 50 ppm/°F, along with either analog or digital outputs. Magnetostrictive Transducers measure the distance between a position magnet attached to the component in motion and the head-end of a sensing rod that is attached to the axis to be measured. The magnet does not touch the sensing rod, so no parts can wear out. The sensing rod mounts along the motion axis and the position magnet attaches to the moving member. An electronics module sends an analog or digital position reading to a controller or receiving device. The electrical connection interface can be either an integral connector or cable and visual diagnostic LEDs to ensure proper wiring, power, and magnet positioning.

Cutaway shows encoder integrat ed into a hydraulic cylinde r. Courtesy of SIKO

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HLT 1300 linear position sensor. Courtesy of Hydac

Encoders are used heavily on mobile machinery. Available with capacitive, optical or magnetic sensing and with incremental or absolute position sensing, these devices accurately determine the stroke of the cylinder. Rotary and linear devices are available, but rotary styles are most common. These devices measure position and resolution in pulses per revolution. Some rotary encoder designs use a wire-actuated sensor mounted directly inside the cylinder. Others are mounted externally. Others are based on Hall-eﬀect, magnetostrictive, or inductive technologies. Linear encoders are available with resistive, capacitive, optical or magnetic sensing with incremental or absolute position sensing to accurately determine the stroke of the cylinder. FPW

SENSING TECHNOLOGIES

Understanding electrical inputs/outputs in sensing technology te d oun in-m der. p g t h ig ylin gineerin htwe nac LL lig ducer o f Rota En trans urtesy o Co

Fluid power systems are crucial in various industries, from manufacturing to transportation. These systems rely on precise control and monitoring to ensure efficient operation and safety. Sensing technology is an integral part of these systems, enabling the measurement and control of fluid parameters. This article will delve into electrical inputs and outputs in sensing technology explicitly used in fluid power. In fluid power systems, sensors convert physical quantities, such as pressure, temperature, flow rate, and position, into electrical signals that can be interpreted and utilized for control and monitoring. These sensors interface the fluid power system and the electronic control system (such as a PLC), facilitating efficient operation and automation. You first need to understand electrical inputs in sensing technology, which refer to the electrical signals received by the sensors of the fluid power system. For instance, a pressure transducer may first sense load pressure at the pump, which is then converted into an analog electrical signal. The PLC interprets the incoming

signal where its programming extrapolates pressure based upon the designated scale. Electrical inputs can take various forms, depending on the type of sensor and the parameter being measured. Standard electrical inputs in fluid power sensing technology include voltage, current, and resistance, and you’ll often find transducers available with 4-20 mA, 0-5 V and 0-10 V. For instance, in a flow sensor, the movement of the fluid generates a voltage or current proportional to the flow rate, which is then used as an electrical input for control purposes. Most sensors must be calibrated, so in this example, the programmer would calibrate the flow sensor to read zero flow at 4 mA and maximum flow at 20 mA. Once the sensor receives the electrical input, it undergoes processing and conversion to generate an output signal. This brings us to the concept of electrical outputs in sensing technology, where electrical outputs refer to the signals the sensor generates in response to the electrical input. These output signals provide valuable information about the fluid parameters being measured. Similar to electrical inputs, electrical outputs can take various forms, depending on the sensor type and application. Common electrical outputs in fluid power sensing technology include voltage, current, frequency, and digital signals. www.fluidpowerworld.com

For instance, a temperature sensor might generate a voltage signal proportional to the temperature, which the control system can then use to monitor and regulate the fluid’s temperature via thermostatic control over the cooling circuit. It’s important to note that electrical inputs and outputs in sensing technology are closely interconnected. The accuracy and reliability of the output signal depend on the quality of the electrical input received by the sensor. Therefore, proper electrical connections and signal conditioning are vital for accurate measurements and reliable control. Moreover, electrical inputs and outputs are subject to signal conditioning and processing techniques to enhance their accuracy and usability. Signal conditioning involves amplifying, filtering, and linearizing the electrical signal to eliminate noise and distortions. The control system can further utilize this processed signal to make informed decisions and adjustments in the fluid power system. In conclusion, electrical inputs and outputs play a fundamental role in sensing technology used in fluid power systems. Transducers convert physical quantities into electrical signals, enabling control and monitoring of fluid parameters. Electrical inputs represent the signals the sensor receives, while electrical outputs are the signals generated in response to the inputs. Understanding these inputs and outputs is essential for optimizing fluid power systems, ensuring accurate measurements, and facilitating efficient control and automation. 7 • 2023

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Hydraulic valves Hydraulic valves, used in conjunction with actuators, help make hydraulics unique in its control of force, torque and motion. Valves govern the direction, pressure and flow of hydraulic fluid, enabling smooth, safe control of actuators. A valve’s purpose may be as simple as relieving pressure to protect your pump and actuator or as complex as electronically controlling both pressure and flow with a proportional valve. A valve circuit may contain a single lever valve or an extensive complexity using a dozen valves per function, as seen in custom manifolds. Directional control valves The directional control valve comes available in myriad configurations and is named appropriately to its primary function, which is to control the path of fluid flow in some way. Directional control valves manage fluid by blocking, diverting, directing, or dumping.

Their complexity varies immensely (just like their cost), as does the integration method. Valve construction runs the gamut from cartridge valves to monoblock valves or subplate mounted valves to inline valves. The operation of a directional valve depends on the industry application in which they are typically applied. For example, directional control valves for log splitters represent the economical and straightforward end. In contrast, servovalves controlling flight simulators perform well at the precise yet expensive niche. You’ll find valves to operate every possible combination of pressure and flow, although extreme combinations of simultaneous pressure and flow are rare. The most basic directional valve is the check valve; it allows flow into one work port and blocks flow coming back through the opposite port. Alternatively, directional valves with complex construction are also common, such as with the pilot-operated valve, which uses a small valve to control a larger one. A standard solenoid spool valve has one directly operated component (the spool) that controls fluid direction when it shifts. As flow increases, the force upon the

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spool also increases, and these flow forces can prevent a spool from actuating, which can be the case with direct-acting electric coils. By using a small pilot valve to control the main-stage spool's movement, the size (and flow) of the valve is nearly limitless. Directional valves are often described by the number of “ways” fluid can travel through them and also by the positions available into which the valve may shift. The ways are equal to the number of work ports, so a 4-way directional valve contains Pressure, Tank and A and B work ports. Positions are equal to the number of positional envelopes. For example, one would describe a double-acting single monoblock valve as “4way, 3-position,” or simply a 4/3 valve. Very few valves offer more than three positions, although the snowplow float valve is one such animal. Directional valves are available in monoblock or sectional valves, common to the mobile-hydraulic industry, as well as subplate mounted industrial type valves such as ISO style D03, D05 and so on. Also common to mobile and industrial markets are cartridge valves installed into manifold blocks.

Cartridge valve manufacturers offer many unique products and allow high levels of creativity with limitless available valve combinations. Inline valves offer a standalone combination of valve with a ported body, which must be plumbed as a separate component not directly interfaced with any other manifold or body. Pressure controls In its most concise description, a pressure valve offers designers an option to limit pressure. Most pressure valves use springenergized poppets pushed against a seat with some form of adjustment screw to modify the spring’s pretension. Pressure valves often use a simple ball and spring configuration or spools for high flow circuits. Relief valve operation is simple: a spring pushes the poppet against a seat, and when pressure from the system is strong enough to counteract the force of the spring, the valve will slowly open, proportionally bleeding off fluid to limit pressure. A relief valve limits maximum pressure for either the entire system or a sub-circuit, with the lowest pressure parallel valve opening first. It is critical

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HYDRAULIC VALVES Yuke np Cour roportio n tesy of AL al valve. A Ind ustrie s

to understand that pressure takes the path of least resistance. Therefore, selecting a pressure valve downstream with a lower setting than the main system relief valve will see all pump ﬂow dump through the valve with the lower setting, thereby leaving no hydraulic energy source for other actuators. Most other pressure valves are based on the relief valve’s simple spring-loaded

ball or poppet construction. Sequence, counterbalance, and brake valves are variations of the relief valve but with added utility or functionality, such as reverse ﬂow check valves or integrated pilot operation. The pressure-reducing valve diﬀers from the other pressure valves because it limits

pressure downstream rather than upstream. Reducing valves are used when sub-circuit pressures need to be lower without sacrificing pressure performance in the rest of the system. Sequence valves operate much as their name suggests — they are pressure valves that remain closed until upstream pressure overcomes the valve’s spring setting. At this point, it simply opens to pass flow to a downstream subcircuit. Sequence valves may be specified with a reverse flow check valve that allows the flow to bypass in the reverse direction. Sequence valves, or any valve with pressure at all work ports simultaneously, should contain a method to drain the spring chamber of trapped pressure. Without a drain, pressure becomes trapped in the spring chamber, which is additive to the spring valves. The result is a valve that opens later than intended or not at all. Counterbalance and brake valves are

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Why do hydraulic valves fail? No matter how well engineered or manufactured, no product has infinite reliability, including hydraulic valves. Valves are critical components in hydraulic systems, responsible for controlling the flow, direction, and pressure of the hydraulic fluid circulating to transmit work. When a valve fails, it can cause system downtime, decreased productivity, and even damage to other downstream components if it releases particles into the hydraulic fluid. Understanding the reasons why hydraulic valves fail can help you prevent these issues from occurring. One of the most common reasons for hydraulic valve failure is contamination. The hydraulic fluid that flows through the system can become contaminated with dirt, debris, and internally-generated metal particles. Suppose contaminated fluid makes its way to the valve. In that case, it may work itself into the small clearances between the spool and body, scoring one or both surfaces, eventually leading to internal leakage. Larger particles may prevent the valve from functioning correctly entirely. Regular maintenance and high-quality filtration can reduce contamination and extend the life of hydraulic valves. Another reason for hydraulic valve failure is general wear and tear. Hydraulic valves are subjected to a lot of stress and strain from

repeated pressure cycles, which causes components such as seals and springs to become worn or fatigued, leading to eventual failure. As well, the electrical coils that activate the valve can burn out over time or even sometimes catastrophically. When you subject a valve to excessive pressure, that type of overloading could fatigue the valve faster at best or break it entirely at worst. In addition, if the valve is subjected to more pressure than it can handle, it can become stuck or damaged, preventing it from opening or closing properly. Proper system design and pressure control can help prevent overloading and extend the life of hydraulic valves. Corrosion is another potential cause of hydraulic valve failure, particularly in harsh environments such as saltwater or acidic chemical environments. Corrosion can weaken the valve and cause it to become brittle, leading to failure, and any rust created is a potential source of contamination for the valve and other components. Should you not avoid a corrosive environment, choose materials for the valve suitable to resist, such as stainless steel. In addition, regular cleaning can help prevent corrosion and extend the life of hydraulic valves. Finally, improper maintenance also contributes to hydraulic valve failure. Lack of regular maintenance, especially with the hydraulic fluid crucial to valve health, is of utmost importance. Failing to follow a regular fluid sample and test program might leave you clueless if the oil needs changing. Even when filtered well, the oil may lose its additives over time, reducing lubricity, corrosion resistance and anti-oxidant capacity. By understanding these factors, you can take steps to prevent valve failure and ensure your hydraulic system continues to operate efficiently and reliably. Proper maintenance, system design, and pressure control are all key to extending the life of hydraulic valves and preventing downtime and damage.

Once hydraulic fluid is badly contaminated, component failures occur more frequently. Courtesy of CD Industrial

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motion control valves designed to safely limit and control loads with overrun potential. Essentially any cylinder that may pull or drop under load, or any motor with constant tension, should use a motion control valve. Installed on the actuator port where load-induced pressure occurs, these are essentially relief valves that require extensively more than load pressure to open directly. More commonly, they take a pilot signal from the opposing work port to open the counterbalance or brake valve using a fraction of the load-induced pressure. This method is safer and more efficient and has the effect of limiting the actuator to a velocity dictated by pump flow rather than load-induced acceleration. Pressure reducing valves remain open until downstream pressure rises above the valve’s setting, an effect much different from other pressure valves, which remain closed until cracked open by pressure. Pressure

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reducing valves may reduce pressure on either work port or the primary pressure port and also perform best when their spring chambers can drain to tank. They operate by modulating incoming flow rate, which in turn reduces downstream pressure. Flow control valves Flow control valves control or limit flow by one of various methods. They are often just a needle valve, which is just a variable restriction, adjusted by a screw or knob much like pressure valves, to restrict the cross-sectional area to reduce flow. When installed with reverse flow check valves, we change the name from needle valve to flow control. Flow control valves can sometimes have multiple ports, such as a priority flow control. They provide controlled, fixed flow to one part of the circuit (sometimes at the sacrifice of another part), but only if input flow is high enough for its priority demand.

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Flow controls are (ideally) pressure compensated, allowing the valve to maintain its set flow regardless of load-induced pressure variances. Pressure compensators are a type of flow control valve available as a single component, often added to other valves in a circuit to provide flow rate accuracy independent of load, such as with an electronic proportional valve. Proportional valves are considered both flow and directional valves to meter flow and control the direction in which flow is metered. Proportional valves use pulsewidth modulation to vary current while they maintain voltage. Varying the current modifies the force of the magnetic field and subsequently how far the spool or poppet moves within its body, changing the size of the opening for fluid to take, which of course, limits flow. A simple variable resistor can limit current, but it is inefficient and cannot provide a PWM controller’s benefits. An electronic valve controller can provide adjustable minimum and maximum settings. A minimum current value is needed to move the spool past its “dead zone” overlap where it “starts” to flow. Also, a maximum current value prevents too much electric juice from fatiguing the valve and coil when only a couple of amps are required to achieve full flow anyway. A proper controller and driver provide a dither signal to the valve, which vibrates the spool so that static friction doesn’t allow the spool to stick inside the body. The spool movement is unnoticeable but is enough so that when a change in current is required, the spool responds rapidly without overshooting the desired new position. FPW

Directional seated valve. Courtesy of HAWE Hydraulik

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Pneumatics overview Pneumatics is a fluid power technology similar to hydraulics in that it transmits force through a pressurized medium to create useful work. However, pneumatic technology differs from hydraulics in its compressibility. Hydraulic oil compresses as well, but only 0.4% every thousand psi or so. Air will compress to half its volume when subjected to double the pressure. Compressibility is an asset for pneumatic systems, allowing for extremely high acceleration and inherent shock absorption. As compressed air moves from high pressure to one of lower pressure, the expansion accelerates the air. The acceleration occurs at the loads of the actuators to provide the snappy movement pneumatic systems are known for. But, of course, the compressibility of air prevents it from being the first choice for load-

holding applications. Still, air-over-oil systems provide a versatile solution when hydraulic power units are unavailable. Pneumatic systems get their power from a compressor that takes air from atmospheric pressure and reduces it to an eighth or less of its original volume. A compressor’s role is singular, and unless your machine uses every cubic inch of compressor air that exists, the compressed air must be stored. Specialized air tanks called receivers act as a buffer between the compressor and the downstream subsystems. This buffer stores the compressed air to reduce the compressor’s load and provides extra capacity when overall demand exceeds compressor capacity. Pneumatic systems operate between 80-120 psi, which depends on the requirements of the loads and actuators in the system. They combine the force and speed advantages of higher pressure with the efficiency challenge of high compression. In other words, above 120 psi, the energy required to further pack air into a smaller space is somewhat of a challenge. Higher compression results in more heat, which adds to the system’s complexity as multiple stages and coolers may be required. Highpressure pneumatic systems also experience a higher risk of leaks and failures, sometimes catastrophic. Actuators can't use air directly from a compressor or receiver. It must first be conditioned to suit each subcircuit or function. Most pneumatic tools, motors, cylinders, effectors and valves prefer clean, dry air with a stable pressure. Therefore, the primary compressor set comes with (or should be optioned with) a pressure regulator set higher than 60

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all others in the plant, a dryer large enough to peak demand, and a filter to prevent any compressor-generated particles from travelling downstream. Because each subcircuit may have separate conditioning needs, individual branches come fixed with their own conditioning components. Filters, regulators, and lubricators offer tailored control over the air quality for each function. For example, a work cell using pneumatic drills and impact guns requires reduced-pressure clean air and air tool oil, which combine to improve performance and reliability. On the other hand, an automated paint booth requires a very high volume of clean, dry air with no lubrication, so understanding the requirements of each air system branch prevents costly design mistakes. Pneumatic applications are diverse. Air process systems, such as sandblasting, are not a fluid power function since air does not achieve work. Pneumatic actuators are incredibly varied — cylinders, motors, clamps, grippers, and rotary actuators. Air cylinders offer quick acceleration for light loads or automated processes, such as packaging equipment, pick-and-place robots, ejectors, or clamps. High-speed, clean air motors can replace light-duty electric or hydraulic motors. Grippers used as robot end effectors provide an inexpensive, rapid method to clamp material for manipulation. Pneumatic clamping solutions include two-jaw parallel grippers or a single pneumatic cylinder against a toggle for high clamping force. Pneumatic actuators and pressure, flow and control valves used to control them may be integrated in many industries. Food & beverage is served by stainless and aluminum components resistant to washdown while offering finishes resistant to bacteria or fungal growth. Medical and pharmaceutical industries benefit from the rapid cycle times provided to robots pressing, punching and ejecting millions of pills or parts. Using a vacuum to move delicate objects without harm offers another trick in the pneumatic hat. FPW

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PNEUMATIC ACTUATORS

Pneumatic actuators Pneumatic actuators take advantage of compressed air to provide your machine with quick and powerful actuation of nearly infinite possible functions. They take the form of cylinders, motors, slides, grippers and rotary actuators, each of which receives pressurized, compressed air to create linear or rotational force. The pistons or vanes of pneumatic actuators produce force when delivered with pressurized air. Because of the compressibility of air, pneumatic actuators are sensitive to both backpressure and flow restrictions. To get around the complexities of variability, we express the forces applied via pneumatic actuators in terms of differential pressure rather than the inlet pressure. In other words, the force generated by a pneumatic actuator is defined by the difference between the pressure at the actuator’s inlet port compared to its outlet port. Because of the relatively clean air operating pneumatic actuators, any leaks result in a loss of performance and reduction in efficiency rather than a possible hydraulic oil leak. However, many pneumatic actuators require lubrication

for performance and longevity, so study your product documentation to check the requirements of your actuator. Pneumatic cylinders The cylinder is the most popular pneumatic actuator — consisting of a piston and rod assembly installed into a barrel and capped on either side to contain both working and load pressure. When one of two ports has directed air from an upstream valve, the cylinder will extend or retract with force equal to the previously mentioned pressure differential factored with the piston’s surface area. A cylinder with a larger bore will have more surface area and, subsequently, more force when applied with a given pressure differential. Cylinders may also be singleacting, pressuring in one direction only while employing gravity or springs to retract. Cylinder bodies must include the mounting method, which is fixed to the machine’s frame or support. Conversely, the cylinder’s rod end attaches to the machine component which moves under load. Should that loaded component move through a radius or arc, the cylinder’s pivot method must be included, such as with a trunnion, clevis or eye.

DSNB actuator for NFPA mounting applications. Courtesy of Festo

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Pneumatic cylinders come in various construction styles: NFPA tie-rod, extruded body ISO, pancake style, and compact round line, to name a few. Unique to pneumatic actuators is the rodless cylinder, which uses a magnet or mechanical coupling that attaches the rodless piston to the mounting platform. They often operate as non-rotating slides for positioning applications. Single-acting cylinders use one air port to allow compressed air to enter the cylinder to move the piston to the desired position, as well as an internal spring to return the piston to the “home” position when the air pressure is removed. Double-acting cylinders have an air port at each end and move the piston forward and back by alternating the port that receives the high-pressure air. Typically, the actuator body is connected to a support frame, and the end of the rod is connected to a machine element that is to be moved. A directional control valve is used to provide a path of compressed air to the extend port while allowing the exhaust air to escape through the valve to the atmosphere. The diﬀerence in pressure on the two sides of the piston results in a force equal to the pressure diﬀerential multiplied by the surface area of the piston. If the load connected

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to the rod is less than the resultant force, the piston and rod will extend and move the machine element. Reversing the directional control valve will provide compressed air to the retract port, allowing exhaust to escape the extend port, and the cylinder will return back to its home position. Pneumatic actuators are at the working end of a fluid power system. Upstream of these units — which produce the visible work of moving a load — are compressors, filters, pressure regulators, lubricators, on-off control valves, and flow controls. Connecting all of them together is a network of piping or tubing (rigid or flexible) and fittings. Pressure and flow requirements of the actuators in a system must be taken into account when selecting these upstream system components to ensure desired performance. Undersized upstream components can cause a pneumatic actuator to perform poorly, or even make it unable to move its load at all. Rotary actuators Rotary actuators transmit torque through a limited rotational arc. Rather than pneumatic motors, which rotate continuously, rotary actuators move a load through a limited range of motion. Some rotate through two discrete positions, while others are capable

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F LUID POWER HANDBOOK of positioning at any angle around the arc. The two most common rotary actuator construction types used in fluid power are the vane and rack and pinion. The vane rotary actuator looks much like an air motor, with a shaft protruding from its mounting face. Two air ports connect internally to the common chamber separated by the vane. Pressure at one port forces the vane towards the opposing port with force equal to the vane’s surface area multiplied by the pressure differential at that chamber. The vane-type rotary actuator makes an excellent two-point operation for industrial automation requiring a load to move quickly between two positions. Although most models offer stroke adjustment, the function pertains mainly to fine-tuning the end-of-stroke position. Rack and pinion rotary actuators are like two air cylinders working in opposite directions and joined at the center by the rack and pinion. As each cylinder strokes, the horizontal motion of their racks forces the

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center pinion to rotate. The torque created is a combination of the cylinders’ forces and the diameter of the pinion gear. Rack and pinion style actuators offer superior side load resistance. The reinforcement from its bearing and abutment of the racks help ensure the load is well-supported. Rack and pinion rotary actuator work well cycling to the end of the stroke and at any point in between. They are not capable of supporting a load mid-stroke like a hydraulic application could. However, with position feedback (like an encoder) and sophisticated control valves, rapid and accurate positioning is possible. Vane-type rotary actuators rarely achieve more than 270 degrees of rotation because their action is like a swinging door. However, rack and pinion actuators are limited only by the stroke of the air cylinders powering them. So it’s not unreasonable to expect a thousand degrees or more of rotation. Accessories improve the function of any rotary actuator. Position switches located

on the body of an actuator may provide a signal for end-of-stroke confirmation for either vane or rack and pinion styles. Many position sensors, such as magnet-sensing reed switches along the length of the rack-andpinion cylinders, may allow discrete positioning anywhere along stroke length. Furthermore, if infinite positioning suits the process, LDTs may be installed to provide an accurate position signal to be relayed to the PLC. Popular applications for rotary actuators are rotary tables, which are used in automation to position workpieces at various work stages as part of a process. In addition, pick and place applications with partial rotation are suitable for vane-type actuators. Other typical applications are tilting, braking, tensioning and lifting. Air motors Some pneumatic actuators operate with rotational torque rather than linear force. Air motors are efficient, high-speed actuators used for drilling, milling, conveying, and tool

Cylinder seal selection Although pneumatic cylinders operate in many conditions, their capacity to withstand the pitfalls of those conditions often comes down to sealing. Performance and longevity of pneumatic cylinders depend on the quality of their seals. A seal’s primary purpose is to contain the compressed air within the cylinder and prevent it from leaking, which reduces efficiency while increasing energy consumption as air passes without doing useful work. First consider operating conditions, which are the most crucial factor when selecting seals for pneumatic cylinders. Next, consider the environment the cylinder will be used in, including temperature range (both internal and ambient), the pressure range the cylinder will see, and exposure to chemicals, dust, moisture, and ultraviolet light. Load requirement is crucial, such as the load’s mass and movement speed. 62

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The seals must be selected to withstand the forces and stresses generated by the load and velocity. With higher pressure, including those created through spikes or intensification, the seals can extrude out small gaps, such as between the piston and barrel. If high velocity is the primary design factor, low-friction seals offer an efficient and reliable solution, which is less likely to subject itself to friction-induced softening. Consider lightly loaded lip seals as opposed to interference fit options like O-rings. The seal’s polymer should be a prime consideration for any pneumatic cylinder application. Common seal materials include nitrile (Buna N), fluoroelastomer (Viton etc.), and polyurethane. Nitrile seals are frequently used in general-purpose applications and offer excellent resistance to oils and fuels. Fluoroelastomer seals are often used in hightemperature applications and have excellent chemical resistance. Polyurethane seals have excellent abrasion resistance and are often used in applications where the load is constantly in contact with the seal. www.fluidpowerworld.com

The seal’s profile is also essential for the performance of the cylinder. The profile refers to the shape of the seal and includes the cross-section, diameter, and overall shape. The profile must be compatible with the pocket or groove it’s installed within and must provide adequate pressure sealing capacity without leakage or extrusion. The seal cavity is a machined pocket to house the seal and keep it firmly in place, and it must neither be too large to allow leakage nor too small as to increase friction. Consider compatibility with lubricants used in the cylinder. Some seals are incompatible with some lubricants, which can cause them to fail. Lubricants that contain solvents, such as mineral spirits or benzene, can attack certain seal materials and cause them to swell or become brittle. Lubricants high in acidity or pH can attack certain seals. Silicone-based lubricants are not recommended for nitrile or fluoroelastomer seals, as they can cause the seals to become brittle and crack over time. Petroleum-based lubricants can attack

PNEUMATIC ACTUATORS operation. They have low inertia, which allows them to accelerate and decelerate rapidly while spinning quickly to high speed. Air motors have many benefits — they offer infinitely variable speed by altering incoming flow and pressure while starting and stopping nearly instantly. Because of the cooling effect of expanding air inside the motor, air motors never overheat or burn out. Additionally, because only air powers these motors, any danger from electrical spark is a non-factor. Finally, air motors are perfect for clean conditions such as food & beverage or pharmaceutical use. By and large, the most common type of air motor used in fluid power is the rotary vane motor. Air motors function when compressed air expands against the vanes of the rotor and will create torque equal to the pressure differential between the inlet and outlet port multiplied by the surface area of the vanes. A rotor with multiple slots and spring-loaded vanes has low inertia, allowing them to start and stop quickly. In addition, low-friction internal components allow some vane motor designs to spin to 20,000 rpm. Higher-powered, heavy-duty air motors are almost always the radial piston type. Vane-type motors rarely achieve more than a few horsepower capacities, but piston motors may output 25 hp or more. More efficient than their vane counterparts, the piston style also offers more torque. Of course, to achieve such high power, radial piston motors require high flow. At peak output, a 25-hp air motor may need close to 700 scfm. FPW

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ﬂuoroelastomer seals and cause them to degrade. Consider the maintenance requirements of the sealing technology as well. Some seals require frequent maintenance, such as lubrication or replacement, while others have a longer service life. If the cylinder is a low-cost option, maintenance may not be a factor, but for expensive NFPA or ISO cylinders, a high-quality design is inﬁnitely repairable. As many as seven or more seals may be used in 7 • 2023

a pneumatic cylinder — piston seals, rod seal, wiper, end seals, and occasionally more. The appropriate piston, rod, wiper, and end seals for pneumatic cylinders are critical to ensure performance and longevity. Considering operating conditions, load requirements, seal material, proﬁle, lubricant compatibility, and maintenance needs, gives your seal its best chance at survival, even in the most demanding application. FLUID POWER WORLD

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FRLs Compressors generate pressurized air, but that exiting air typically contains dirt and water. Before it can travel downstream to valves and actuators, it must be filtered, regulated and sometimes lubricated. Otherwise, left untreated, it can damage products, cause premature component wear, attack seals and cause them to leak, and permit rust and corrosion in tools and piping — all leading to faster breakdowns and higher maintenance and operating costs. An air line filter traps particle and liquid contamination in compressed air. It captures solid particles (dust, dirt, rust), and also separates liquids (like water and oil) entrained in the compressed air. Filters are installed in the line upstream of regulators, lubricators, directional control valves, and air-driven devices such as cylinders and motors. There are three types of filters: general purpose, coalescing and vapor removal. General purpose filters are used to remove water and particles, coalescing to remove oil, and vapor removal to evacuate oil vapor and odor. Pressure regulators reduce and control fluid pressure in compressed air systems. Regulators are also frequently referred to as PRVs (pressure reducing valves). Optimally, a regulator maintains a constant output pressure regardless of variations in the input 64

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pressure and downstream flow requirements, so long as upstream pressure doesn’t drop below that of downstream. In practice, output pressure is influenced to some degree by variations in primary pressure and flow. Pressure regulators are used to control pressure to air tools, impact wrenches, blow guns, air gauging equipment, air cylinders, air bearings, air motors, spraying devices, fluidic systems, air logic valves, aerosol lubrication systems, and most other fluid power applications requiring subordinated pressure. Regulators employ a control-spring acting upon a diaphragm to regulate pressure, and its spring rate determines the range of pressure adjustment. General purpose regulators are available in relieving or non-relieving types. Relieving regulators can be adjusted over a wide pressure range, and even when downstream flow is blocked at the reducing valve, relieving regulators will allow the excess downstream loador head-induced pressure to be exhausted. Non-relieving regulators, when similarly adjusted, will not allow the downstream pressure to escape. The trapped air will need to be released by some other means; for example, by operating a downstream valve. A lubricator adds controlled quantities of oil or other lubricant into a compressed air system to reduce the friction of moving components. Most air tools, cylinders, valves, air motors, and other air-driven equipment require

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FRL compressed air service unit. Courtesy of Festo

lubrication to extend their useful life. The use of an air line lubricator solves the problems of too much or too little lubrication that arise with conventional lubrication methods, such as either grease gun or direct oil application. Once the lubricator is adjusted, an accurately metered quantity of atomized lubricant is supplied to the air operated equipment, and the only maintenance required is a periodic refill of the lubricator reservoir. Adding lubrication to a system also “washes away” compressor oils that travel through the system in vapor form. Mineral oils added to the system prevent synthetic compressor oil build-up on system components. When lubricators are not used in a system, a coalescing filter should be installed to remove compressor oil aerosols.

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Pneumatic hose & tubing Imagine you’re in charge of automating a factory or warehouse. You need to move products quickly and efficiently from one point to another and consider pneumatics as a solution. Pneumatic systems need plumbing, lots of it. The most popular plumbing conduit for air systems is synthetic plastic or rubber tubing or hose. However, with so many types of pneumatic hose available, how do you choose the best one for your application? Let’s start by looking at the factors you should consider when selecting a pneumatic hose. Firstly, you need to consider the flow rate of your components and actuators and, therefore, the pneumatic hose. For example, if you have high-volume production lines or need to move large actuators quickly, you’ll need a pneumatic tubing with a high flow rate to ensure you provide your machines with the flow they need to do the job. Secondly, you need to consider material composition because it plays a part in flexibility, durability, weight, and compatibility with external factors. The chosen tubing material is crucial for food and beverage applications, where you need to use foodsafe compounds that will not leave toxic residue. For example, you don’t want to use pneumatic tubing that could contaminate your food or beverage products, which is the case with PVC —hence it is not recommended. Polyurethane hose is widely used in automation and robotics applications due to its high flexibility, durability, and resistance to abrasion, chemicals, and UV rays. It is also suitable for use with compressed air systems and in the food and beverage industry (think CO2 lines for soft drinks). Nylon tubing is commonly used in pneumatic systems for its high resistance to pressure, excellent flexibility, and solid durability. But, again, it is also suitable for use in compressed air systems and the food and beverage industry (think CO2 lines for beer). Polyethylene material is excellent for various pneumatic applications due to its flexibility, www.fluidpowerworld.com

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low weight, and resistance to chemicals and impact. Teﬂon is a plastic unmatched for hightemperature applications and in environments where chemicals are present due to its high resistance to both. They are commonly used in the chemical, pharmaceutical, and food and beverage industries. Thirdly, you need to consider the pressure rating of the pneumatic hose. Not all tubing provides the same pressureresisting capacity, especially in more exotic applications that are hot, cold, or exposed to ambient chemicals. In addition, tubing is rated with consideration to a safety factor, so be sure to select the hose for its working pressure rather than its maximum pressure. Fourthly, you need to consider the size and length of the pneumatic tubing. Longer tube will

have more cumulative pressure drop, so you may need to choose a larger size to accommodate. Also, consider if the hose is stationary or moves frequency, such as in cable carriers. A rigid hose such as Teflon might not last as long as a more flexible choice such as nylon. Finally, you should balance the previous considerations with cost. Pneumatic tubing is available at a range of price points, and you need to select one that fits within your budget but still meets your needs. Many fluid power distributors will offer bulk discounts for purchasing rolls of tubing rather than smaller sections. If your shop builds a lot of equipment, you’re likely color-coding your tubing. Although no industry standards exist for air lines, it is common to use red for pressure and blue for atmosphere.

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How can you prevent pneumatic tube failure? Pneumatic systems are common in various industries, including automation, food & beverage, and packaging. They’re preferred over other systems for their simplicity, efficiency, cleanliness, and versatility. Pneumatic systems rely on hoses to transport compressed air from the compressor to the devices that use it. There are many types of hose, each with unique properties and applications. However, pneumatic hoses are prone to failure over time, like any other mechanical component. Therefore, it’s essential to understand the types of failures that may occur and how to prevent them. Here are some of the most common types of pneumatic tube failure and how to prevent them. One of the most common types of pneumatic tube failure is abrasion. Abrasion occurs when the hose rubs against another surface, causing it to wear out over time. Abrasion also occurs from friction between the hose and other components, such as fittings or the machinery itself. To prevent abrasion, consider using abrasion-resistant hose, protective sleeves, or installing the hose in a way that reduces contact with other components. Kinking occurs when a hose bends too sharply, causing it to collapse or form a permanent bend. In addition, kinking can restrict airflow or damage the hose, leading to a loss of pressure as it leaks. To prevent kinking, install the hose correctly, with gradual bends and no sharp angles. All tubes have a minimum bending diameter, and any bends tighter than recommended could lead to a kink. If the hose needs to bend sharply, consider using a female-to-female elbow or installing a swivel joint. When a hose is compressed or flattened, either by vacuum or by the weight of other components, it can be crushed. Crushing can damage the hose, restrict airflow, or cause leaks when repeated events eventually lead to fatigue. To prevent crushing, ensure that the hose is installed in a way that reduces contact with heavy components. Consider using a protective sleeve or routing the hose to reduce external pressure. Chemical damage occurs when a hose is exposed to chemicals that degrade its polymer. This can cause the hose to weaken, crack, or become brittle, leading to leaks or failure. To prevent chemical damage, consider hose resistant to the specific chemicals in your environment. If the hose must be exposed to chemicals, ensure it is cleaned and maintained regularly. Aging is a reality for pneumatic tube and occurs when a hose degrades over time due to exposure to sunlight, heat, or moisture. Aging causes the hose to become brittle, lose elasticity, or crack, leading to leaks or failure. To prevent aging, consider using hoses designed for outdoor use or with UV-resistant properties. Store hoses in a cool, dry place and avoid exposure to direct sunlight or heat sources. And inspect hoses regularly. 66

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VACUUM COMPONENTS

Vacuum components Vacuum is pressure that is

lower than atmospheric — 14.7 psia at sea level. In a vacuum system, the difference between atmospheric and vacuum pressure creates the ability to lift, hold, move, and generally perform work. There are two types of vacuum applications: closed, or nonporous; and open, or porous. In a closed system, removing air progressively decreases the air density within the sealed, confined space and creates a vacuum. In an open system, a vacuum unit must remove more gas molecules than are able to leak back into the system. Vacuum is typically divided into three areas of application, depending on the level of vacuum required. Low-level vacuum applications are typically those requiring high flows and low force. These systems are primarily serviced by blowers. Screen printing on cloth is one application that falls into this range. The majority of industrial vacuum falls within the range of 6 to 29.5 in.-Hg. Application examples include pick-and-place and thermoforming. Scientific or process applications encompass the deepest levels — approaching a near-perfect 29.92 in.-Hg. Flow in this range is minimal. Examples of

applications are ion implantation and space simulation. The vacuum generators that evacuate air and create the required low pressure come in an extensive array of types, sizes, designs and efficiencies to suit widely ranging applications. Two basic types are electric-motordriven vacuum pumps and vacuum ejectors. Vacuum pumps. Mechanical vacuum pumps generally fall into one of two different types: positive-displacement and dynamic/kinetic. Displacement vacuum pumps essentially operate as compressors with the intake below atmospheric pressure and the output at atmospheric pressure. They draw in a fairly constant volume of air, which is mechanically shut off, expanded, and then ejected. The main feature of vacuum pumps of this type is that they can achieve a high vacuum with low flow rates. Types include reciprocating piston, rotary vane, diaphragm and rotary screw. They are often suited for precision industrial applications. Kinetic vacuum pumps cause gas particles to flow in the delivery direction by applying additional force during evacuation. Rotary blowers, for example, operate according to the impulse principle: a rotating impeller transfers kinetic energy by impacting air molecules. In

VX multi-stage vacuum pump. Courtesy of COVAL

FLIW (Foam Lip Wide) piGRIP series of foam suction cups. Courtesy of Piab

operation, air is drawn in and compressed on the suction side by the impeller blades. These vacuum pumps generate a relatively low vacuum, but at high flow rates (high suction capacity). They are usually suited for handling extremely porous materials, such as clamping cardboard boxes. Among the advantages, typical positive-displacement industrial pumps generate up to about 98% vacuum — beyond the capability of ejectors. And blowers can offer high suction rates well beyond 1,000 m3/hr. However, electromechanical vacuum pumps tend to operate continuously with vacuum requirements regulated by valves. And compared to ejectors, they are larger, heavier, and usually cost more. Vacuum ejectors. Vacuum ejectors basically generate vacuum using pneumatically driven nozzles without moving parts. They produce high vacuum at relatively low flow rates. A classic ejector consists of a jet nozzle (also called a Laval or venturi nozzle) and, depending on the design, at least one receiver nozzle. Compressed air enters the ejector and a narrowing of the jet nozzle accelerates the flowing air to up to five times the speed of sound. The ejector has a short gap between the jet-nozzle exit and

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the entry to the receiver nozzle. Here, expanded compressed air from the jet nozzle creates a suction effect at the gap which, in turn, creates a vacuum at the output vacuum port. Vacuum ejectors come in two basic versions, single and multi-stage. A single-stage ejector includes a jet nozzle and one receiver nozzle; a multistage ejector has a jet nozzle and several nozzle stages, each of which has a larger diameter in proportion to the falling air pressure. Air drawn in from the first chamber, combined with compressed air from the jet nozzle, is thus used as a propulsion jet for the other chambers. In both versions, air exiting the receiver nozzle generally discharges via a silencer or directly to the atmosphere. Among their benefits, vacuum ejectors are compact, lightweight, and relatively inexpensive and they respond quickly, with fast start and stop times. They resist wear, can mount in any position, experience no heat build-up in operation, and consume energy only as needed — as they switch off when no vacuum is needed. On the downside, vacuum ejectors only generate pressures to about 85% vacuum, and do not produce extremely high suction rates.

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Pneumatic valves Compressed air pneumatic

systems require methods of safe and precise control of actuators unique to their accoutrement. Although the medium is fluid, just as hydraulic or process water systems, the execution of control is different in many ways. What is shared in the conduction of any fluid power medium is the need for valves to control force, velocity and direction of movement. Air preparation Pressure relief valves will control pressure at their inlet port by exhausting pressure to atmosphere. Relief valves are typically used only in receivers or air storage devices, such as accumulators, as a means to prevent excessive pressurization. As such, relief valves are often called safety valves and are not typically appropriate for use anywhere but the air preparation stage. Pressure regulators in pneumatic systems limit pressure downstream of the unit by blocking pressure upstream at the inlet. Regulators are used in the air preparation stage, as well as in control of cylinders and motors. The

letter R in the acronym FRL stands for regulator, which is installed downstream of the receiver tank, but before the circuit they are regulating. Sometimes multiple stages of pressure reduction are required, especially with a large centralized compressor and receiver feeding various workstations. A regulator can control pressure within the main grid of distribution plumbing, but sometimes air is piped directly to an FRL at each workstation or machine. Pressure at this main header could be 120 psi or more, but a branch circuit could be regulated at 90 psi, for example. Most regulators are capable of relieving downstream pressure, which prevents that downstream pressure from elevating as a result of load-induced pressure or thermal expansion. Pressure regulators can be had as stand-alone units, but sometimes a ﬁlter is attached to kill two birds with one stone. Regulators are most often available as a component of a modular set, with a ﬁlter, regulator, lubricator or dryer etc., and can be assembled in

CPX valve manifold configuration for Emerson DeltaV DCS systems. Courtesy of Festo

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any combination. The regulator will have an inlet port, outlet port and a port for the pressure gauge, which they are most often included with. Pressure regulators can also be used to control pressure for individual actuators, such as an inline regulator or workport mounted regulator. These are typically quite small and included with reverse flow check valves, as would be required for double acting function of a cylinder, for example. Further still, differential pressure regulators are offered by some manufacturers, to maintain a set pressure differential between the two ports, rather than just maintaining downstream pressure. It should be noted that all pressure regulators are adjustable, most often with screws or knobs. Flow controls Also common in pneumatic systems are valves to control flow. Fewer are available compared to pressure or directional valves, but most circuits apply them for easy adjustment to cylinder or motor velocity. Controlling velocity in pneumatic systems is more complex than a hydraulic system, because pressure differential between the work ports of a cylinder plays a larger part. Flow control valves for pneumatics are simple, usually available in two configurations used in two different ways. One configuration is merely a variable restriction, with a screw or knob adjustment to open and close a variable orifice; this is also often referred to as a needle or choke valve. The other type introduces a check valve, which allows free flow in one direction,

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Stepper 12 proportional flow control valve. Courtesy of Spartan Scientific

and restriction in the opposing direction. For whatever reason, this valve has hijacked the name flow control all for itself. Flow control valves are applied in two different ways; meter in or meter out. Meter in is the method of controlling the rate of airflow as it enters a motor or cylinder. When metering in, a cylinder will move rapidly with high force and efficiency, but the motion of the piston is prone to spongy and unpredictable movement. When metering out, the cylinder velocity is more stable and repeatable, but efficiency and dynamic force are lost to the energy required to push past the flow control. Most applications operate using meter out flow controls, because disadvantages are easily overcome by increasing upstream pressure. A method of increasing cylinder velocity, for double acting or spring-return cylinder retraction functions, is to add a quick exhaust valve to the cap

PNEUMATIC VALVES

What are electropneumatic flow controllers? An electropneumatic flow controller provides precision control of the flow of a gas to an actuator — representing the latest flow control option. They are most commonly used to control the flow of air to an actuator; thereby controlling the speed which the actuator extends/retracts or rotates. To appreciate the advances that electropneumatic flow valves provide, it is important to understand the mechanical technology they are built upon. A simple way to control the flow of gas to an actuator is a needle valve. This requires a person to manually turn a knob that gradually slides a needle into an orifice reducing the flow. A limitation of this method is that the air going into and out of the actuator is controlled by the same valve. The next advancement in flow control was the integration of a check valve into the valve. This allowed for control of the flow into or out

of the actuator with the return path can open and pass around the orifice. While both valves provide excellent speed control of actuators, their limitations result from their manual adjustment and one flow point. A common issue in pneumatic systems is that as the actuators wear, the speed is reduced, the seals wear and the flow controls need adjustment. An electropneumatic flow control provides an automated process for adjusting the flow control addressing the wear example and helps maintenance of the machine by providing early warning of service or replacement needs on the actuators. They can control the speed of an actuator using a sensor for a feedback loop. For example, in a pneumatic cylinder with a linear position transducer sending the location cylinder rod as it extends, the electropneumatic flow valve can provide more air, which allows the cylinder to rapidly extend and then slow down when reaching a point where the cylinder is to generate force.

Manifold, DIN rail and panel mounting are valuable options for many applications. Units like the MM closed-loop valve offer electronic control of pressure and provide flexibility with mounting and accurate, repeatable, customizable pressure control from vacuum through 175 psig. Courtesy of Proportion-Air

Pilot Operated Pneumatic Check Valves with Both Manual and Pilot Release Capabilities NU-CHECK

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DUAL-CHECK

Checks both sides of a pneuma�c device to stop and hold movement in either direc�on ®

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FEATURES Ball and seat style check provides bubble �ght seal Self-cleaning design highly tolerant to dirt and debris Standard 3-year warranty

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F LUID POWER HANDBOOK side work port. Because cylinders retract faster than they extend as a result of differential air volumes, it is harder to evacuate the cap side air volume without oversized valves or plumbing. A quick exhaust valve vents directly to air from the cap side work port, and reduces the backpressure created upon retraction, permitting very rapid piston velocity.

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Directional control valves Pneumatic directional valves are available in many sizes, styles and configurations. At the basic end of the spectrum is the simple check valve, which allows free flow in one direction and prevents flow in the reverse direction. These can be installed anywhere from right after the receiver to within a flow control valve itself. As directional valves grow in complexity, they are specified under a general naming practice related to the number of positional envelopes of the valve and the number of work ports in the valve, and specifically in the order described. For example, if it has five ports, port 1 will be for pressure inlet, ports 2 and 4 for work ports, and 3 and 5 for the exhaust ports. A valve with three positions will have a neutral condition, extend condition and retract condition. Putting it all together, this describes a five-way, three-position valve, also referred to as a 5/3 valve. The common configurations seen in pneumatics are 5/3, 5/2, 4/2, 3/2 and sometimes 2/2 valves. Also part of the description of a directional valve is its method of both operation and positioning. The valve operator is the mechanism providing the force to shift the valve between its positions. The operator can be a manual lever, electric solenoid, an air pilot, or cam mechanism, to name a few. Some valves are a combination of these, such as a solenoid pilot valve, which is a tiny valve providing pilot energy to move the main-stage valve. Positioning of any valve is achieved by either a spring, such as with a 5/2 spring-offset valve, or with detents in 5/2 detented valves. A 5/2 spring-offset valve will return to its starting position when energy is removed from its operator, like de-energizing the coil, or removing pilot pressure. A 5/2 detented valve will stay in the position it was last activated to until the operator switches it again. Pneumatic valves are manufactured in various incarnations. Poppet valves are simple, using a spring to push a face of the poppet down on its seat. Construction can be metal-to-metal, rubber-to-metal or even with diaphragms. Poppet valves can often flow in one direction, just as a check valve, but need to be energized to flow in reverse. They are limited to two- or three-way port configurations, although they can mimic four- or five-way valves when used in parallel. They offer typically high flow conductance for their size, and are generally very resistant to contamination. Spool valves use a notched metal cylinder that slides within a precisely machined body, drilled with three to five ports, or even seven ports if the valve is pilot operated. Low-end valves consist of only a spool and body, and are prone to internal leakage. Better valves use seals in the body or spool to prevent leakage between ports. High-end spool valves are constructed with precision, often requiring fine lapping procedures during manufacturing, and with their

ACCURACY REPEATABILITY CUSTOMIZATION

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PNEUMATIC VALVES tight tolerances, often require few seals, improving reliability and longevity. Other forms of high-end valves use a sliding block of metal or ceramic, which is not only efficient, but also extremely resistant to contamination, making them great for dirty environments. Proportional valve technology Proportional valves are considered both flow and directional valves to meter flow and control the direction in which flow is metered. Proportional valves used pulse width modulation to vary current while they maintain voltage. Varying the current modifies the force of the magnetic field and subsequently how far the spool or poppet moves within its body, changing the size of the opening available for fluid to take, which of course limits flow. A simple variable resistor can limit current but it is inefficient and cannot provide a PWM controller’s benefits. Older proportional valve designs employed a spool valve with metering notches and PWM ready coils to infinitely vary the spool position. The performance level of these proportional valves left much to be desired but was the least expensive option to vary flow and direction simultaneously. Having no way to control accuracy in the face of changes in pressure drop, the actual flow rate through a prop valve will vary based on changes in flow, system pressure, and load pressure. For proportional valves to achieve any level of performance close to a motor-based servovalve, advanced electronic control was required. Because a standard coil powered prop valve was susceptible to flow forces, the feedback method was required to maintain the spool in its desired position. Linear differential transducers came to the rescue to monitor spool position down to microscopic distances. The transducer signal feeds back into the valve’s onboard electronics and when it senses the spool outside of its desired position, the valves adjust the PWM output to the appropriate coil to bring it back in line with the desired position. Proportional valves have evolved to be quite sophisticated. The frequency response, accuracy, and hysteresis come close to flapper valve performance and sometimes even surpasses them. In fact a whole new breed of valves, called high response, have taken the proportional valve to near servovalve performance. A high response valve is a relatively new term used to describe valves whose performance is variable, dynamic, and powerful. Previously only servovalves running technologies such as a torque motor could be classified as high response but with the proliferation of contemporary electronics, feedback, and programming, proportional valves have closed the gap. Now some proportional valves match the performance of servovalves. New designs can include self-contained media separated 7 • 2023

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electronic proportional flow control valves. Using different positions or steps, these valves can precisely regulate flow output and require minimal power to maintain a desired position, maximizing energy savings Proportional valves in many cases look exactly like the spool valve they’re based upon — cartridge or CETOP valves, for example, are hard to tell apart from their bang-bang counterparts. Proportional valve spools require metering notches so Dual-check valves. that even a minute valve shift allows a Courtesy of ALADCO throttled volume to flow. Proportional valve coils must translate their incoming power signals into a variable magnetic field that tugs the plunger which in turn shifts the spool to varying degrees. The pulse width modulated signal produced by the electronic valve controller maintains a constant voltage that varies the length of time the signal is on. By varying the pulse width, the valve controller essentially varies the current to the valve to control the strength of the magnetic field, thereby the metered flow output from the valve. FPW

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Accumulators Hydraulic accumulators are devices that store and discharge energy in the form of pressurized fluid. They’re analogous to rechargeable batteries or capacitors in electrical systems, and they are often used to improve hydraulicsystem efficiency. These pressure vessels hold hydraulic fluid and a compressible gas, typically nitrogen. The housing or shell is made of materials like steel, stainless steel, aluminum, titanium, and fiber-reinforced composites. Inside, a moveable or flexible barrier — usually a piston or rubber bladder — separates oil from the gas. In these hydropneumatic units, hydraulic fluids only compress slightly under pressure. In contrast, gases can be compressed into smaller

volumes under high pressures. The re-expansion of the gas is what supplies energy back into the system. Potential energy is stored in the compressed gas and released on demand to force oil from the accumulator and into a circuit. To use the device, the gas volume is first precharged — generally to around 80 to 90% of the minimum system working pressure. This expands the gas volume to fill most of the accumulator with only a small amount of oil remaining inside. In operation, the hydraulic pump raises system pressure and forces fluid to enter the accumulator. The piston or bladder moves and compresses the gas volume because fluid pressure exceeds the precharge pressure. When a downstream action such as actuator movement creates system demand, hydraulic system pressure falls and the accumulator releases the stored, pressurized fluid to

the circuit. Then the charging cycle begins again. Three types exist: bladder, piston and diaphragm accumulators. Bladder accumulators use a flexible closed bladder inside the shell to separate the gas and fluid. They usually have large ports that permit rapid fluid discharge and help ensure that the device is relatively insensitive to dirt and contamination. Bladder-type accumulators are usually designed to have a 4:1 pressure ratio (maximum pressure to gas-charged pressure) to protect the bladder from excessive distortion and material strain. Experts tend to view bladder accumulators as the best general-purpose units. They come in many standard sizes, and good response characteristics make them suitable for shock applications. A bladder can be easily replaced in the event of failure or damage. Courtesy of GPM Controls

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Piston accumulators are much like hydraulic cylinders without the rod. Similar to other accumulators, a typical piston accumulator consists of a fluid section and gas section, with the movable piston separating the two. Less common are piston accumulators that replace highpressure gas with a spring or heavy weight to apply force to the piston. Piston accumulators are generally recommended for large stored volumes — to 100 gallons or more — and can have high flow rates. Pressure ratio is limited only by the design, but they’re usually not recommended for shock applications. They are often built for rugged, heavyduty operations. However, they are more sensitive to contamination that can damage the seals — although most piston accumulators are readily repaired by replacing the piston seals. Diaphragm accumulators operate much like bladder accumulators. The difference is that instead of a rubber bladder, this version uses an elastic diaphragm to separate the oil and gas volumes. Diaphragm accumulators are economical, compact and lightweight devices that offer relatively small flow and volume typically to around one gallon. A diaphragm accumulator can handle higher compression ratios of up to 8 to 10:1 because the rubber barrier does not distort to the same degree as a bladder. They also enjoy wide mounting flexibility, are insensitive to contamination and quickly respond to changes in pressures, making them suited for shock applications. FPW

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ACCUMUL ATORS

What are accumulator safety blocks? Hydropneumatic accumulators combine the power density of hydraulics with the compressibility (and expandability) of air. The accumulator itself uses either bladders, diaphragms or pistons to separate the gas side from the hydraulic side. The air side is pre-charged with nitrogen gas to a pressure appropriate for the application. Nitrogen is used for its non-reactive nature and may be charged up to 2,000 psiI or more. The gas volume of an accumulator may range from fractions of a liter up to 15 gal or more, allowing about a third of such volume to be used as hydraulic ﬂow, give or take.

Internal to the valve block is a series of valves Accumulator to passively and actively control the energy state safety blocks. Courtesy of the accumulator. A locking ball valve provides of Parker the first line of defence – a technician who Hannifin performs maintenance on the machine may lock the accumulator into the tank drain position to guarantee the accumulator cannot be charged should the machine inadvertently be turned on. Once maintenance or service completes, the technician removes the lock and closes the valve, so the accumulator again holds pressure. A second ball valve installed into the manifold closes to block incoming pump fluid, providing important redundant safety for the machine and technicians alike. A relief valve installed parallel to the ball valves limits pressure inside the accumulator. It must be set higher than the system relief valve to prevent pump pressure from draining directly to the tank. The optional solenoid valve, as discussed earlier, provides yet another safeguard to ensure no energy remains stored when you shut the machine down. A pressure gauge in the accumulator port offers a visual guarantee that the accumulator remains drained.

During operation, pressurized fluid is directed into the accumulator, which compresses the nitrogen until the gas compresses to the point that its pressure equalizes with system pressure. Once downstream pressure drops below system pressure, such as when a function is activated, the compressed gas forces hydraulic fluid from the accumulator’s fluid port. The vigor in which the accumulator sends fluid depends on the pressure differential at the downstream load or restriction. Because accumulators store potential energy much like an electrical capacitor, the possibility of accidental discharge must be respected. In fact, a large accumulator storing hydraulic fluid under high pressure may release the entirety of its energy within seconds, equating to perhaps hundreds of horsepower in some cases. The possible danger is very real, and all precautions must be taken to safely and reliably contain the accumulator’s stored energy. Should one or more accumulators exist DON’T JUST GO WITH THE FLOW in your hydraulic circuit, special valves must be installed to control and direct accumulator energy. Then, when the machine shuts down, either intentionally or via an emergency stop, operators and service personnel need not guess if the accumulators contain potentially dangerous pressurized fluid. A normally open solenoid valve teed off from the accumulator pressure port should open to direct fluid to the reservoir as a default safety feature. Such a valve should also include an orifice to prevent saturation of the tank line and potentially damaging return line filters or other equipment downstream. Although designing a safety circuit for an accumulator would be relatively straightforward, time and cost can be saved by purchasing a stand-alone accumulator safety block. These safety blocks contain all the necessary valves and components to keep the accumulator safe when not in operation. The blocks generally have three ports, one pressure out, one for the reservoir and a third close-coupled to the accumulator itself.

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Miniature fluid power controls

Microhydraulics

Miniature flow controls. Courtesy of The Lee Co.

Fluid power systems are noted for their high power density — permitting high force and torque output from relatively small components when compared to electromechanical systems. Microhydraulics makes it feasible to obtain a significant amount of force from a minimal power source within a very restricted space envelope. Thus, it can provide a straightforward solution to problems that are often beyond the limits of traditional mechanical options. In many cases, these systems are ideally suited for wideranging applications like medical orthotic and prosthetic equipment, human-assist lifts, exoskeletons, hand tools, rescue robots, aircraft and missiles, race cars and oceanographic instrumentation. Engineers might be tempted to simply downsize typical commercial components when the need arises to 74

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control motion and force in very small powered systems. However, the reality is a bit more complex because scaling laws are not intuitive, according to researchers Jicheng Xia and William Durfee of the University of Minnesota. For example, they note that in a cylinder, force is proportional to area (L2) while weight is proportional to volume (L3). On the other hand, the thickness and weight of a cylinder wall required to contain a fixed pressure goes down with bore size. Thus, the final weight of a hydraulic system at small scale cannot be determined by proportionally scaling a large system. Also, the fundamentals associated with pressuredriven flow dictates that high pressures are required to permit high flow rates through micro-sized channels. In laminar-flow conditions, an order-of-magnitude decrease in the hydraulic diameter of a channel increases by two orders of magnitude the pressure difference required to maintain a constant average flow velocity.

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Another critical barrier for increased hydraulic power density at reasonable efficiency is the seals. Surface effects such as friction drag of seals and viscous drag of gaps become significant in small bores and that impacts overall efficiency. Too tight and friction dominates; too loose and the pressurized fluid will leak past the seal. Cost and power consumption are also important considerations. Fortunately, a number of manufacturers have designed or re-engineered hydraulic components to work on a “miniature” scale. As one example, Bieri Hydraulik, a unit of Hydac International, makes six standard versions of Type AKP microaxial piston pumps designed with three or five pistons. For instance, the 5-piston Size AKP36 pump measures only 1.4 in. (36 mm) in diameter by 3.9 in. (99 mm) long. It features a displacement of 0.36 cm3/rev with 250 bar maximum pressure and 4,000 rpm max speed. The Size AKP103 measures 1.9 in. (50 mm) in diameter x 3.8 in. (98 mm) long. It has 3 pistons, displacement of 0.1 cm3/rev, 500 bar max rated pressure, and runs at speeds to 5,000 rpm. A 5-piston version offers displacement of 0.3 cm3/rev. The quiet-running units reportedly offer high volumetric efficiency even at minimum speed of 100 rpm. They are valve controlled on pressure and suction side, so are not suitable as motors. The small units are used in offshore and oil and gas

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applications, in metering systems, and general hydraulics systems with small displacements. Hydro Leduc offers a complete range of fixed and variable displacement micropumps; micro-motors (speeds from 350 to 6,500 rpm); check, pressure-relief, solenoid and pilot valves; and complete micro-power packs for operating in widely varied working environments. For example, its PB32 fixed displacement micro-pump has a body diameter of only 1.28 in. (32 mm) with displacement as small as 0.0007 in.3, maximum speed of 5,000 rpm continuous and 6,000 peak, and maximum pressure of 4,350 psi continuous and 5,075 psi peak. A slightly larger PB33 HP version has a 0.0027 in.3 displacement and a maximum continuous pressure rating of 13,050 psi and max peak of 14,500 psi (1,000 bar). The Lee Company. makes an array of miniature, high-performance fluid control components, including Lee Plug expansion plugs, solenoid valves, flow restrictors, safety screens, relief and check valves, and shuttle valves. The company’s flow controls, to cite one typical product, offer metered flow in one direction and free flow in the opposite direction. It’s also called a one-way restrictor. In the smallest size, diameter is only 0.18 in., yet nominal system pressure rating is up to 3,000 psi. Other similar-size products include poppet-style check valves that can flow one gpm at 25 psid and have a nominal system pressure rating up to 4,000 psi; and pressure relief valves that

MINIATURE CONTROLS have cracking pressures from 20 to 100 psid and, in some versions handle nominal system pressures up to 5,000 psi. Some miniature check valve and restrictor models can even handle system pressures up to 8,000 psi. Likewise, safety screens as small as 0.13 in. diameter help protect orifices, relief valves, and other sensitive hydraulic components. Critical components are often relatively immune to low levels of small-size contaminants, but a single large particle can cause sudden failure — possibly with catastrophic effects. While filters maintain fluid cleanliness during operation, safety screens provide an added level of protection. The units come with hole sizes from 0.0008 in. to 0.062 in., and highpressure versions won’t burst or collapse at pressures of 7,500 psid, even if fully clogged.

SFC Koenig offers a range of plugs, flow controls, check valves and related components. The Expander plugs, for instance, reportedly seal drilled holes with excellent reliability. They come in sizes from 0.093 to 0.875 in. and are rated to 6,500 psi (450 bar) for push-type units and 7,200 psi (500 bar) for pull versions. Its stainless-steel Restrictor units provide precise flow control in fluid systems and are available in sizes as small as 0.093 in. (4 mm) in expander and threaded styles, and handle pressures to 2,900 psi (200 bar). Orifice can be specified to achieve desired flow rates. Check valves, 0.216 in. (5.5 mm) diameter, handle forward or reverse flow, have a cracking pressure of 2 to 29 psi (0.14 to 2 bar) and maximum working pressure of 4,352 psi (280 bar).

Takako Industries, a member of the KYB Group, claims to make the world’s smallest axial-piston pump. The square TFH-040 unit measures only 1.18 in. (30 mm) wide by 3.0 in. (77 mm) long and is rated for a maximum working pressure of about 2,030 psi (140 bar). Displacement is 0.4 cc/rev, input speed is to 2,000 rpm, with a flow rate of 0.8 lpm. The unit is part of a family of micropumps which feature a hybrid drive system that combines the benefits of hydraulics with the controllability of an acservomotor and inverter to satisfy a range of specifications with a small-volume pump. Typical applications, Takako says, include a pump for valve controls, mold switching equipment for forming machines, hydraulic clamps, and crimping presses. FPW

Miniature pneumatics

Cordis electronic pressure controls. Courtesy of Clippard

In the realm of fluid power engineering and manufacturing, innovation knows no bounds. The advent of miniature pneumatics has ushered in a new era of precision and efficiency, enabling a wide range of industries to benefit from compact and surprisingly powerful pneumatic systems. These miniaturized marvels have found their way into various sectors, using low to medium pressure and serving as the backbone for countless lightand medium-duty applications.

Miniature pneumatics refers to the design, development, and application of pneumatic systems at a significantly reduced scale compared to traditional pneumatic systems. These systems utilize compressed air or gases to generate force, motion, or pressure in a precise and controlled manner. With advancements in manufacturing techniques and high-quality materials, miniature pneumatic components have become more reliable, compact, and cost-effective than ever before. The medical industry dramatically benefits from miniature pneumatics due to the need for precise control and compact,

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F LUID POWER HANDBOOK quiet devices. Applications range from surgical instruments, drug delivery systems, and prosthetics to respiratory devices, diagnostic equipment, and laboratory automation. Miniature pneumatic systems ensure accuracy, responsiveness, and safety, making them indispensable in critical healthcare settings. Because of the ingenuity of engineers, methods to reduce power consumption (such as magnetically latched solenoid valves) provided medical equipment manufacturers with compact and portable devices not previously possible. Portable oxygen delivery systems are now small, portable and quiet, so patients are no longer bed-ridden when requiring oxygen supplementation. Many batterypowered pneumatic devices aid emergency workers as well as long-term care workers. Portable ventilators, nebulizers, and suction devices are just a few life-saving machines created from low-power, miniature pneumatic components. Miniature pneumatics also play a crucial role in robotics and automation, where size, weight, and efficiency are paramount. These components enable precise movement, gripping, and actuation in small robotic systems, such as drones, industrial automation, and robotic prosthetics. Their ability to deliver high force and rapid response makes them invaluable in achieving delicate yet dynamic tasks. The electronics industry demands precision and reliability in manufacturing processes, and miniature pneumatics rise

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to the occasion. They are used in pick-and-place machines, micro-electro-mechanical systems (MEMS), and semiconductor fabrication equipment. Miniature pneumatic components enable precise handling, positioning, and inspection of delicate electronic components, ensuring high-quality production with reduced risk of damage. The aerospace and defense sectors benefit from miniature pneumatics in various applications, including flight control systems, unmanned aerial vehicles (UAVs), missile guidance systems, and parachute release mechanisms. Miniature pneumatic components offer rapid response times, compact designs, and the ability to operate in extreme environments, making them ideal for critical aerospace and defense operations. Nearly every heavy-duty pneumatic component has a miniature counterpart:

Miniature valves control the flow of compressed air or gases in pneumatic systems. They come in various configurations, including solenoid, check, proportional, and shuttle valves. These valves provide precise regulation and quick response times, crucial for miniature applications where space is limited. Many miniature components come available as cartridge valves, allowing machine manufacturers to create custom compact manifolds to reduce plumbing or insert the valves into custom actuators as well. Miniature cylinders convert compressed air or gases into linear motion, enabling actuation and movement in confined spaces. They are available in different types, including single-acting, double-acting, rotary, and compact cylinders. Miniature cylinders offer high force-to-size ratios and exceptional precision for controlled motion applications. Miniature air motors offer high-speed, precise control for rotary applications, such as dental tools or medical saws. Conversely, tiny air motors used to accurately control liquid dosing systems or sample manipulation equipment turn very slowly and take advantage of extremely quiet and smooth operation. Miniature air preparation units ensure the quality and cleanliness of the compressed air supplied to miniature pneumatic systems. These units consist of filters, regulators, lubricators, and pressure gauges. By removing impurities and regulating air pressure, miniature air preparation units enhance the performance and longevity of miniature pneumatic components. Miniature fittings and tubing are required for miniature valves and actuators. They require appropriately sized plumbing, so miniature fittings and tubing provide the necessary connections and pathways for the flow of compressed air or gases. Depending on the application and work environment, they come in various materials, such as stainless steel and polymer. FPW

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WE INNOVATE. Imitation is easy. Innovation is hard work. Leighton Lee II was an innovator. He founded our company on that spirit, and it’s how we solve tough problems today. Every product you see here—from miniature check and relief valves to shuttle valves, flow controls, precision orifices and plugs—was developed to solve a customer’s fluid control challenge. Since 1948, we’ve been delivering engineered solutions for a wide variety of demanding applications. We have the experience, product breadth, and technical know-how to provide engineered performance, with zero risk. Don’t let an imitator ruin your day—or your design. Contact us today to put our knowledge to work for you. 2 Pettipaug Rd, Westbrook CT 06498-0424 860-399-6281 | 1-800-LEE PLUG | www.theleeco.com

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Shock absorbers Machine builders are always on the lookout for ways to run equipment faster and increase

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throughput and productivity. However, components moving at high speeds often must decelerate and stop without damaging the equipment or payload. Otherwise, the consequences are excessive loads, vibration and noise that can compromise safety and

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Determine kinetic energy in the system from:

machine reliability. Ek = W/(722)(V2) Engineers can sometimes dampen motion with products like inexpensive elastomeric bumpers, simple air cushions, or gas-spring linear dampers. But these typically have a limited ability to absorb energy and decelerate objects. Shock absorbers, in contrast, provide controlled deceleration by converting kinetic energy to thermal energy. In action, motion applied to a hydraulic shock absorber’s piston forces pressurized fluid through specially designed internal orifices. That restricts flow and generates heat which, in turn, transfers to the metal body and dissipates to the environment. After impact, a spring typically returns the piston rod to the starting location. Shocks are used in a wide range of applications, from automotive manufacturing and lumber processing to robots, cranes and packaging equipment. When choosing a shock absorber, one must specify the stroke length, compressed length, extended length, cylinder (body) diameter, and rod diameter. The stroke length is the distance between the compressed and extended length. The cylinder diameter is an important factor in determining whether the cylinder will fit into the desired location, and how the shock absorber will be affixed to the adjacent structure. How do you size a shock absorber? Sizing a shock absorber is relatively straightforward. Several reputable manufacturers offer online calculators, but here are a few guidelines to quickly come up with suitable products for a given task. Manufacturers’ web sites and data sheets typically list products by parameters like stroke, usable velocity range, maximum amount of energy that can be absorbed per cycle, maximum force capacity, and the maximum propelling force it can handle, as well as dimensions and other relevant

details. Before sizing a shock absorber, however, users ﬁrst need to determine the relevant operating conditions, including the weight and velocity of the moving mass and how frequently the shock is loaded. For simplicity, let’s look at a linear-motion application and use Imperial units for the calculations.

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where Ek = kinetic energy, lb-in.; W = weight of moving mass, lb; and V = velocity of moving mass, in./sec. This equation represents the amount of kinetic energy that the shock absorber will convert to thermal energy on each impact. Next calculate the work energy in the application, deﬁned as the amount of energy an external device generates to move the load: Ew = Fd(S) where Ew = work or drive energy, lb-in.; Fd = drive force, lb; and S = stroke of the shock absorber, in. Note that Fd should not exceed the unit’s maximum rated propelling force. If it does, select a larger size and recalculate the work energy. The next step is to calculate the total energy, Et (lb-in.) per cycle, shown as: Et = Ek + Ew Again, if this exceeds the model’s energy-absorbing capacity, select a larger unit and recalculate the work energy. Otherwise, the shock’s temperature may rise beyond rated limits and critical internal components like hydraulic seals could fail. If the application uses more than one shock absorber, divide the total energy Et by the number of shocks to determine the total energy per shock. Then determine the total energy a unit must convert in one hour. That’s because even though a shock might absorb an acceptable amount of energy in a single impact, it might not be able to dissipate the generated heat if the cycle rate is too fast. Here, multiply Et by C, the total number of cycles per hour: Etc = Et(C)

SHOCK ABSORBERS

Fp = Et/(Sη) where S = the stroke of the shock absorber and η is the unit’s damping efficiency. While the efficiency can vary with the type and model, 85% efficiency is a good baseline for typical industrial shocks. This is important when selecting a suitable shock absorber because the machine structure and mounting must have the necessary strength and rigidity to withstand the transmitted force. The efficiency of various units is measured by evaluating how much of the shock’s stroke is used for actual damping of the motion. Shock absorber efficiency increases as more energy dissipates over the stroke, and more-efficient products typically yield the lowest shock forces for a given stroke. Considerations such as the machine’s structural integrity and the payload’s ability to withstand forces without damage are also key to successful damping configurations. And some applications or payloads may have specified g-load rating limits. For example, an

operator housed in a large overhead crane must be protected from excessive g-forces. Calculate this g-load from: g = (Fp – Fd)/W The above calculations help ensure that a given shock absorber meets all operating parameters. Again, make certain that the selected model matches or exceeds requirements for energy absorbed per cycle and per hour, as well as the shock force. Otherwise, it will likely cause damage or fail prematurely. Shock absorbers may be made from aluminum, steel and stainless steel, or thermoplastic. Steel is used when high strength is required. The other materials provide varying balance between strength, weight, corrosion resistance and cost. Additionally, the rods can be treated with chrome to provide corrosion resistance and increase surface hardness. Nitride will increase the hardness by introducing nitrogen into the outer surface of the rod. There are also a number of important shock absorber features to consider. Adjustable shock absorbers allow the stiffness of the response to be monitored and finetuned. This is usually accomplished by adding or removing hydro/pneumatic medium from the shock absorber by way of a valve. Locking capability allows the position of the rod to be fixed at a given position. FPW

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when performance matters Industrial shock absorbers Industrial gas springs Vibration isolation Buy Online Standard products available

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PET shock absorbers. Courtesy of ACE Controls

The device’s hourly capacity must exceed this calculated amount. If not, choose a larger absorber (and recalculate Ew if the stroke changes) or, possibly, add an external oil tank or a cooling device to help dissipate the heat. Finally, consider the shock force, Fp (lb) in the application. Shock force, in essence, is the resistive force required by the shock absorber to stop the moving load:

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