fluid power world handbook june 2015

June 2015www.fluidpowerworld.com

2015HANDBOOKFluid Power

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2 FLUID POWER WORLD 6 2015 fluidpowerworld.com

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

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

Fluid power is, quite simply, the use of a liquid or a gas to move a load and accomplish work. The technology is used in countless industrial as well as everyday environments, from automobile assembly lines to passenger airliners and from packaging equipment to huge earth-moving pieces of equipment. Fluid power can be used for extremely tough tasks, such as boring new underground mining tunnelsor for very gentle operations, such as lifting and stacking large sheets of glass. Through various components and actuators, fluid power systems can push, pull, lift, rotate or grip almost any load.

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

Fluid power systems are comprised of a myriad of components, including pumps, cylinders, valves, hose, fittings, gauges, sensors, filters, seals and reservoirs. Some components are considered absolute necessities, while others are optional and used to refine the system for more precise operation or to increase the lifespan of the system or its individual parts. Throughout this handbook, we will detail many of the more

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

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

And fluid power is an important technology. A 2012 study by the Department of Energy discovered that between 2.0% and 2.9% of the United States energy is transmitted through fluid power equipment. While that is an impressive statistic, the study also found that the efficiency of fluid power averages 22%.

While that percentage is low, it also illustrates how much improvement there is to make. The study concludes that a 5% improvement in efficiency over 5 years is possible by instituting best practices in industry. Or, even better, a 15% improvement over 15 years is possible with a strategic R&D program. Doing this would save the U.S. an amazing $37 billion.

While some say that fluid power is a static, mature technology, theres still a lot in store for the technology. As the Internet of Things continues to dominate the engineering news, were slowly seeing hydraulic and pneumatic components become more Internet-friendly, wireless and capable of being monitored and controlled from distant locations. Were eagerly watching to see what the coming years will bring to the world of fluid power. FPW

Fluid Power OVERVIEW

Paul J. Heney Editorial [email protected] @DW_Editor

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02 Fluid Power Overview06 SMART TECHNOLOGY14 Gauges18 Safety24 Shock Absorbers and Linear Dampers

26 Pneumatics Overview27 Air Brakes28 Air Compressors32 Air Springs34 Compact Cylinders - Actuators36 Cylinders - Pneumatic Actuators39 Cylinder Slides/Rodless Cylinders - Pneumatic41 FRLs44 Grippers - Pneumatic47 Miniature Pneumatics50 Vacuum Components52 Valves - Pneumatic

57 Hydraulics Overview58 Accumulators61 Bar Stock62 Clutches and Brakes64 Cylinders - Hydraulic 71 Filters - Hydraulic74 Filtration Systems78 Fittings and Flanges - Hydraulic86 Fluids - Hydraulic88 Grippers - Hydraulic90 Hose - Hydraulic94 Hose Couplings - Hydraulic99 Manifolds - Hydraulic104 Motors - Hydraulic108 Pressure Transducers112 PTOs and Gearboxes116 Pumps - Hydraulic122 Replacement/Rebuilds126 Rings128 Rotary Actuators - Hydraulic132 Seals136 Valves - Hydraulic

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Smart Technology

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fluidpowerworld.com 6 2015 FLUID POWER WORLD 5

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EDITORIAL

Editorial Director Paul J. Heney [email protected]@dw_editor

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2011, 2012, 2013,2014

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

FLUID POWER WORLD is also an independent forum for the expression of opinions relevant to industry issues. Letters to the editor and by-lined articles express the views of the author and not necessarily of the publisher or publication. Every effort is made to provide accurate information. However, the publisher assumes no responsibility for accuracy of submitted advertising and editorial information. Non-commissioned articles and news releases cannot

be acknowledged. Unsolicited materials cannot be returned nor will this organization assume responsibility for their care.

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

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Smart Technology:

Michelle DiFrangia Assistant Editor

6 FLUID POWER WORLD 6 2015

Its closer than you think

The HyQ or Hydraulically actuated Quadruped robot helps humans during search and rescue operations. Moog developed the Highly Integrated Smart Actuator, which is integrated into the legs of the robot, to aid it in navigating rough and uneven terrain. The custom-designed hydraulic actuator incorporates a sensor network, onboard loop closure for force, position and velocity control and EtherCat interface into one unit.

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WE ARE IN THE MIDST OF ANOTHER INDUSTRIAL REVOLUTION, BUT THIS ONE HAS US WITH OUR HEADS IN THE CLOUDS AND OUR HANDS READY TO CUT THE WIRES.

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

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

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

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

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




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

Vast quantities of data can be overwhelming. Training is key to getting the most out of an IoT integration, said Edwards. It is important to train staff to handle the increase of software and electronics on these products, and the data and analytics they provide. This will allow customers to take true advantage of the opportunities the IoT offers.

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

So where will IoT hold the most value? Are certain components better suited for integrating this technology? Some say yes, while others arent as ready to call out specifics.

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

Hoxie also points to components that are naturally more sensing oriented, such as control elements, as being more compatible. However, he also said that components that have not historically seen controls, like hoses, can now be incorporated into the IoT and offer significant value.

Alternatively, King doesnt think any one component of fluid power is more compatible than another. Its not the component that is important, but what that component does that matters, he said, echoing his thoughts on Big Data. If the component is critical to the customers operations, it should be connected to the IoT so new insights can be derived that help improve the users experience.

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

EATON HYDRAULICSPRODUCT: LifeSense Hydraulic Hose Condition Monitoring System

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

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

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

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

But what about the risk factors associated with storing information on

the Cloud? Alex Edwards, manager, Software, Electronics and Controls Center of Excellence at Eaton Hydraulics, offered


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BOSCH REXROTHPRODUCT: Hydraulic Power Pack

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

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all more or less equally suited from a technology standpoint, provided electronics have bought their way into them already. As far as better suited, with respect to adding value to have a device as part of the IoT, it is hard to say because the IoT experience base is so limited at this time.

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

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

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

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

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

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

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

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

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



fluidpowerworld.com

termtrend,onewhichwemaynotfullyunderstandtheimpactofuntilweareusingthenextgenerationofhydraulicproductsandcomponents.

In10years,itwillcompletelytransformhowpeoplewillinteractwithmachines.Agreatplacetoseethisisagriculture,whetheritissmarttractorsthathelpoptimizeplantingandcropselection,orgrainbinsensorstoreducespoilage,addedKing.

Langropointedoutthatsomeindustryexpertspredictcompleteimplementationofmanufacturingfacilitiesin15to20years,whileothersexpecttoseethetransitionsooner.

Regardlessoftimeframe,onethingiscertain:OncethefulleconomicvalueoftheIoTisrealized,implementationonsomelevelwillbecomealmostmandatory.

AnypieceofequipmentshippedfromnowonthatisnotabletoupgradeitselftosupporttheIoTtechnologyevolutionwillberemovedfromservicebeforetheendofitsdesignlifeandreplacedbysomethingthatcansupporttheup-to-dateIoTstandardsandfunctionality,saidRey.

ItlookslikeitssafetosaythatifyourenotactivelyresearchingtheIoT,youshouldbe,andyourcustomersprobablyalreadyare.FPW

Some industry professionals might argue that

electronics has an advantage over fluid power

when it comes to implementing the IoT. What are

your thoughts?

Jeremy King, Bimba Manufacturing

It is as easy to get data from a fluid power device

as it is from an electronic device. One has to

simply integrate the sensors and connect them

up. Providing data to the IoT is trivial; it is having

people who understand what that data means

that is important. In many ways, fluid power

engineers have the advantage of knowing a lot

more about the entire system so they can derive

deeper insights from the data.

Ben Hoxie, Eaton Hydraulics

We see electronics and fluid power as integrated

solutions. Machines will continue to need the

power and efficiency hydraulics provides, but with

powerful intelligence electronics software pro-

vides. The future is in coupling these capabilities

together for maximum configurability, efficiency,

intelligence and power.

Frank Langro, Festo

I tend to agree that the electronic-based products

have a leg-up, so to say, in that they have an

inherent ability to transfer data that a purely

pneumatic product might not have. However,

the integration of pneumatics and electrics has

evolved and will continue to evolve, making it

feasible to integrate sensors and communications

into traditionally dumb products like air supply

units or cylinders.

Gonzalo Rey, Moog

It is hard today to find a piece of a fluid power kit

that does not have electronics. If the question

means pure electronics then one element of

their advantage is that their obsolescence horizon

is much shorter than for a fluid power installation.

That makes it easier to keep the installed base

up-to-date with the IoT, and therefore, a lot easier

to support. To combat this, fluid power devices

must support safe and convenient field upgrades.

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

R

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2000

1000

0 5000psi

4000

3000

GAUGES

A pressure gauge is a fluid intensity measurement device. Pressure

gauges are required for the set-up and tuning of

fluid power machines, and are indispensable in troubleshooting

them. Without pressure gauges, fluid power systems would be both unpredictable and unreliable. Gauges help to ensure there are no leaks or pressure changes that could affect the operating condition of the hydraulic system.

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

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

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

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

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


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

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

They are many types of gauge styles, the most common being Bourdon tubes and bellow gauges. Bourdon tubes function by taking the pressure and converting it into mechanical energy. This energy moves a dial in the gauge, displaying the current amount of pressure in the system. Bourdon tube gauges are currently some of the most common gauges and have different configurations such as curved, helical and spiral. The different style of tubing, the size of

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

Bourdon tube operation is simple. They consist of a semicircular and flat tube of metal, fixed at one end and attached

to a sensitive lever mechanism at the other. As pressure increases inside the tube, the force of the fluid attempts to straighten out the

curved tube. The tube then pulls away from the lever, which being connected to the needle on the display, shows the pressure at the fluid port.

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

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

Most pressure gauges in North America come with a 14-in. NPT male, but SAE thread is gaining popularity. The use of test-point adapters at various locations on the hydraulic system allows for measurement during troubleshooting without having to purchase dozens of pressure gauges. The test-point fitting attaches to the gauge, which can be screwed onto the test points throughout the circuit, allowing you to connect under pressure to measure at various points in the system. Most gauges are 212 in. in diameter, and can be either top-mount or panel-mount styles, but gauges are available in every size, material and construction imaginable.

Whether used for testing equipment or operating machinery, the right pressure gauge helps reduce costly downtime. In mechanical gauge applications for hydraulic systems, the common threats to gauge reliability are vibration, pulsation and pressure spikes. Therefore, its best to look for gauges designed specifically for hydraulic applications. These features include: a forged brass case to prevent resonant frequencies from destroying internal components; a liquid-filled case to protect the gauge from vibration and extreme pressure cycles; and a restrictor to prevent damage to the gauge from pressure spikes. Although the liquid used in the gauge varies from application to application, glycerin is commonly used and performs well in many conditions. The higher the viscosity of the liquid, the more it dampens the vibrations. When choosing between a dry, water- or glycerin-filled gauge, it is also important to consider the following: temperature range, needle response time required, changes in pressure and the amount of vibration expected from the application.

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

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

Several standards (including ISO 13849-1:2006, ANSI/ASSE Z244.1-2003 [R2008] and ANSI/PMMI B155.1-2011) define the control system as including not only input, sensing and interlock devices, but also output devices such as pneumatic and hydraulic valves.

The function of a fluid control valve mimics that of an electrical-control relay and, therefore, is subject to the same rules for classifying safety integrity. Thus, properly specified machine safeguarding systems include provisions for pneumatic valves, including:

must be functionally redundant must be monitored for faults (including

diminished performance faults, which may create the loss of redundancy), without depending on external machine controls or safety circuitry

must return to a safe position in the event of a loss of pressure or other such event

must be able to inhibit further operation upon detection of a fault condition until such condition is corrected

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

Two general abnormal conditions can affect valve safety. The first is similar to an electrical-control fault, such as when a relay might be stuck in the open or closed position. The second abnormal condition is when a valve develops diminished performance, as when it becomes sticky or sluggish. In such cases, the valve reaches the proper position, but slower shifting affects safe stopping distances or precise timing. The ANSI B11.19-2010 standard mandates a monitoring system that detects these conditions for critical applications and the ANSI/PMMI B155.1-2011 standard requires diminished performance monitoring if stopping time can be affected. An easy solution is to use a self-monitoring, Category-3 or -4 valve, designed to detect both conditions.

The use of double valves remained relatively unheard of for many years, except in a few select industries, such as stamping presses, which first initiated control reliability requirements. Double valves provide dual internal functions (redundancy) so that an abnormal function of one side of the valve does not interfere with the overall normal operation. At the same time, the double valves sense abnormal operation on either side of the valve and then inhibit further operation until the problem has been corrected and the valve deliberately reset. This sensing and inhibiting function is commonly referred to as monitoring.

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

should have a dedicated, specific function-reset input and should prohibit the ability to perform a reset by simply removing or re-applying pneumatic or hydraulic power, and

must not automatically reset.

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

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HYDRAULIC SAFETY:

Safehydraulicsinvolvestheconsiderationofasafemachine,firstandforemost,andthisisregardlessoftheformofmotivation.

Thetwomostcriticalconsiderationsinhydraulicsafetyarewithcontrolofflowandpressure.Safecontrolofloadsbeingmanipulatedbyhydraulicsisoftenprimary.However,thesafecontainmentofpressurizedfluidoftenmeansloadsarealsostable,asacatastrophicleakoffluidcouldcauseafailureofthesystemtocontroltheload.

Safecontrolofahydraulicloadinvolvesensuringfluidisaccuratelymetered.Thepotentialforpressureand/orload-inducedpressuretoimpartenergyintooilishigh.Assuch,theoilwantstogiveupthatenergytotheambientsurroundings,butispreventedfromdoingsobyonlytheintegrityofthecomponentsandconduitsofthehydraulicsystem.Thepressureeitherwantstoescapepastflowcontrolordirectionalvalves,oritattemptstoexittoatmospherethroughsealsorplumbingfailurepoints.

Whenfluidiswellcontrolledthroughsomesortofmeteringdevice,suchasaflowcontrol,counterbalanceorproportionalvalve,theactuatorsandloadsarepreventedfromrunningaway.Forexample,whenacylinderisinstalledroddown,andloadsaretypicallyintension,itisofteninstalledwithameter-outconfigurationtopreventtheloadfromrunningawaywiththecylinder.Althoughitisasafemethodtopreventarunawayload,rod-sidepressureintensificationcanbearisk.Ifintensificationblowsoutpistonseals,thentheloadcandropregardless,whichiscounterproductivetothemeter-outphilosophy.

Toavoidthepitfallsofmeteringout,acounterbalancevalvecanbeusedinstead.Thecounterbalancevalveisconsideredapressurevalve,butinreality,itcontrolsthespeedofanactuator.Thesevalvesensureacylinderwillonly


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move as rapidly as pump flow is dictating, regardless of load-induced pressure or intensification. If a pilot signal is not seen from the opposite work port, the valve remains shut, preventing the load from dropping. Often mounted directly to the cylinder work port, the counterbalance valve also prevents dropping loads when hose or tube failures occur.

A leak in the cylinder hose or tube can also cause catastrophic failure and personal harm. When fluid is free to exit the actuator at a broken conduit, it can no longer hold a load up. The counterbalance valve prevents the load from dropping should there be a conduit failure. A pilot-operated check valve will provide the same safety function of a counterbalance valve, but is designed for static load-holding. It will hold a load indefinitely, but is not as smooth at controlling

load-induced movement as the latter valve is.Pressure is the very essence of a hydraulic system,

and it is required to provide the force density that makes a hydraulic system so effective. But pressure can easily rise through intensification, load spikes, water-hammer, and thermal expansion, to name a few. If pressure isnt controlled and limited, components can fail, seals can give way and either example can render a machine unsafe. For this reason, hydraulics uses many types of pressure control valves.

Relief valves are used to limit pressure, preventing damage and limiting power requirements. A relief valve is often used to control main system pressure or isolated sub-circuits. Some circumstances require sub-circuits to operate at different pressures than others, and the pressure-reducing valve can achieve

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this.Itlimitspressuredownstreamofitself,andinsomecases,canbeareducing-relievingvalveaswell.Thistypeofvalvecancontroldownstreampressurespikesorthermalexpansion,whereheatedfluidincreasesinpressure.Somehydraulicsystemscanuseacombinationofvariouspressurevalvestoensurecircuitpressureissafelylimitedateverypartofthemachine.

Sobycontrollingbothpressureandflowinahydraulicsystem,bestpracticesofsafetycanbeobserved.Amachinefailureisunsafeinthebestscenarios,soensuringahydrauliccircuitisdesignedforsafetywillpreventinjurytooperators.

doublevalveprovidingthiscriticalfunction.Bysimplyincorporatingtwostandardairvalvesintothecircuit,noprovisionismadetosensetheabnormaloperationofonesideofthevalveor,evenmorepreferable,diminishedperformancesuchasslowshifting.Inaddition,thereisnoprovisionforinhibitingfurtheroperationofthecircuituntilthevalveisrepaired.Ifonevalveactuatesabnormally,thesecondonecontinuestofunctionandredundancyislost.Thecircuitdoesntrecognizelostredundancy,norwouldithaltoperationsasawarningthatredundancyhasbeencompromised.Then,ifthesecondvalvealsoactuatesabnormally,thereisnobackup,andcontrolintegritynolongerexists.

Doublevalvesareappropriateforpneumaticandhydraulicequipmentanytimereliabilityisanissue.Typicalapplicationsincludee-stop,two-hand-control,lightcurtains,safetygates,pneumaticlockingdevicesforsafetygates,hydraulicbrakes,airbrakes,amusementrides,hoists,elevators,pinch-pointapplications,oranyotherapplicationwherecontrolsystemintegritydependsonvalveoperation. FPW

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Shock Absorbers & LINEAR DAMPERS

6 2015 FLUID POWER WORLD 25

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

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

WHAT ARE THE SELECTION CRITERIA?The general criteria when selecting a shock absorber are the dampening method and damping direction. The dampening method can be elastomeric, pneumatic or hydraulic. The damping direction can be either in compression or extension.

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

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


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

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

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

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

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

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

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

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

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

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

More and more, pneumatics is being used in interesting ways that would have been unthinkable a decade or two ago. Creative applications from robotics to pneumatic muscles are consistently making the news, showing not only the creativity of the engineering community, but also the inherent flexibility and adaptability of this important technology. FPW

PneumaticsOVERVIEW

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Air brakes & CLUTCHES

AIR brakesserveasthemainbraketoprovideparkingandE-stopbrakingfunctionsinavarietyofapplications,includingdraglines,grindingmillsandshovelsinmining,drawworksfordrillingrigs,andmarinewinches.Theyprovidethequickactuationandstoppingtimesthatarenecessaryinemergencysituationsortostoplargeindustrialmachinesforroutinemaintenance.Theyareactuatedwithcompressedairratherthanhydraulicfluidoroil.

Airclutcheshelptransfertorquebetweentheengineandtransmission,ratherthanprovidingstoppingpower.Theyrelyoncompressedairforengagementanddisengagement.Bycontrollingtheairpressureappliedtotheclutch,youcanachievesmoothcontrolleddecelerationandevenrapidstops.Inaddition,theyofferquickandsafedisengagement.

Airbrakesarerotorsordiscsattachedtoadrivelineshaftthat,whenthebrakeisapplied,bringtherotatingmachinerytoastop.Whenthebrakeisapplied,apistonispneumaticallyactuated,forcingthefrictionpadstoclamptherotordiscs.Severalfactorsgointosizinganairbrake;mostnotably,therequiredhorsepower,stoppingtimeandtotalenergyaremustsforselectingtherightbrakefortheapplication.

Drum-styleconstrictingclutchesarepneumaticallyactuatedandareusedtoconnectanddisconnecttorotatingshaftstotransmitpowerandmotion.

Air-actuatedbrakesandclutchesofferanumberofadvantages,suchasfastresponseratesandsafe

operation.Sincetheyarepneumaticallyactuatedversushydraulicallyactuated,theriskofspills,leaksandfiresiseliminated.Leakedorspilledoilcancreateanincidentthatcantakehoursordaysofdowntimetocleanup,createsahazardousworkingenvironmentandputsendusersatriskofexpensiveenvironmentalfines.

UnlikeelectricaloptionssuchasvariablefrequencydrivesandotherACdrivemotors,airbrakesarecapableofnotonlystoppingmotion,butalsomanualoperationinthecaseofapowerfailure.Electricaloptionsareusuallymorecomplexasaresult,andmayrequiresometypeofafail-safebraketosloworstopmotionincase

ofpoweroutage.Tomeettheneedsofmorecomplex

machinery,newerbrakesandclutchescanincludesensingandmonitoringtechnologytomakethe

equipmentmoreresponsiveandabletoprovidefeedbackorwarnusersofproblems.Solutionsonthemarkettoday

includebrakeandclutchproductswithembeddedtemperaturesensorsorslipdetection.FPW

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AIR COMPRESSORS

AIR compressors supply the compressed air flow for all pneumatic equipment in a system. The compressor adds energy to the air, which is cleaned and conditioned by filters and dryers, then transmitted in piping for use by tools, equipment and processes. Compressed air is an energy intensive source of process power, about 7 to 8 units of energy are consumed at the compressor for each unit of mechanical energy produced by a typical compressed-air powered deviceand of this, typically 50% of the compressed air is wasted due to leakage and inappropriate use. Most of the energy released by an air compressor is in the form of heat of compression.

When discussing compressed air flows, there are various definitions that relate to compressor capacity:

ACFMactual cubic feet per minute (also called free air delivered, FAD, or inlet cubic feet per minute, ICFM). This is the flow of air taken in by the compressor at site conditions (local atmospheric pressure, temperature and humidity). In general, higher altitudes, temperatures and levels of humidity reduce the capacity of the compressor to produce a given mass of compressed air; therefore, if these conditions exist, a larger compressor must be purchased.

CFMcubic feet per minute. This is the flow of air at a certain point at a certain condition, which must be specified. With regard to sizing air compressors, it is important to understand the wide range of conditions at which the CFM can be stated.

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

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

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

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

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

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Aircompressorsrunmostefficientlyatfulloutput,butthereisseldomademandforfulloutputonacontinuousbasis.Forthatreason,theoutputflowandpressuremustberegulated,usuallybyoneofseveralmethods:

On/off operationmotoronsmallercompressorsisstartedandstoppedtomaintainpressureLoad/unloadinletairvalveisopenedorclosedtomaintainpressureModulationinletairvalveiscontrolledproportionallybychokingofftheinletflowtomaintainoutputpressureVariable displacement controldisplacementofthecompressionchamberisreducedtoproducealowerflowandconstantpressureVariable speed controlthespeedofthecompressionelementisvariedtoadjusttheoutputflowandtomaintainconstantdischargepressure

Shortfallsofthestart/stopandload/unloadmethodsincludehighermechanicalwearandtearonmotorsandbearings.Withload/unload,evenduringunloadedoperation,themotordrawssubstantialpowerwhileperformingnousefulfunction.Modulationcontrolistheleastefficientwaytocontrolacompressor,withthepowerinputdroppingoffonly3%forevery10%decreaseinflow.Variabledisplacementcontrolprovidesabetteralternativefortheupper50%ofcapacity,butduringlowdemand,powerconsumptioncanstillbesignificant.

Often,anefficientalternativeistousevariablespeedcontrol,wherethepowerdropsinalmostdirectproportiontotheflowreduction.Thiscontrolisusuallyaccomplishedusingavariable-frequency(speed)drive(VFDorVSD).Energysavingsof20to30%andhighercomparedtoothermethodsofcontrolarecommonwhenthiscontrolisusedonsystemswithvaryingload.Otherbenefitsincludelesswearandtearoncompressorcomponents,duetosofterstartsandeliminationofcycling;lowerpeakdemandforelectricpower;quieteroperation;andimprovedpowerfactor.VFDcontrolsrequiregoodenvironmentalconditionsandgoodmaintenancetoensuretheyaretroublefree.

REDUCING ENERGY COSTS WITH BETTER CONTROL

withtheairtoseal,lubricateandremovetheheatgeneratedbycompression.Thisfluidformsathinfilmbetweentherotorsthatvirtuallyeliminatesmetal-to-metalcontactandwear.Thefluidisseparatedfromthecompressedair,cooled,filteredandreturnedtotheinjectionpoint.Thecompressedairpassesthroughanafter-coolerandwaterseparatortoreduceitstemperatureandwatercontentsoitisreadyfortheairtreatmentequipment.

Becausethecoolingtakesplacerightinsidethecompressorpackage,theworkingpartsneverexperienceextremeoperatingtemperatures.Therotarycompressor,therefore,isacontinuousduty,air-cooledorwater-cooledcompressorpackage.Advantagesoftherotaryscrewcompressorincludesmooth,pulse-freeairoutputinacompactsizewithhighoutputvolumeoveralonglife.

Rotaryscrewaircompressorsareeasytomaintainandoperate.Capacitycontrolforthesecompressorsisaccomplishedusingseveralmethodswithvaryinglevelsofefficiency;therefore,itisimportanttoconsiderwhattypeofcontrolistobeusedinasystem(seesidebar).Ingeneral,variablespeedandvariabledisplacementcontrolsarethemostefficientwaystorunrotaryscrewcompressorsatpartialloads.

Oil-freerotaryscrewaircompressorsusespeciallydesignedairendstocompressairwithoutoilinthecompressionchamber,yieldingtrueoil-freeair.Oil-freecompressorsaretypicallytwo-stageunitsandaremorecostlythanlubricatedtypes.Oil-freerotaryscrewaircompressorsareavailableasair-cooledandwater-cooled,withbothload/unloadandvariablespeedcontroloptions.Theyalsoofferthesameflexibilityasoil-floodedrotarieswhenoil-freeairisrequired.

Reciprocatingaircompressorsuseapistonwithinacylinderasthecompressinganddisplacingelement.Single-stageandtwo-stagereciprocatingcompressorsarecommerciallyavailable.Single-stagecompressorsaregenerallyusedforpressuresintherangeof70to100psigandtwo-stagecompressorsaregenerallyusedforhigherpressuresintherangeof100to250psig.Thesetypesofunitsaremostoftenusedforsmallersystems.Typically,thesecompressorsarenotratedforcontinuousdutyduetolimitedcoolingmethodsandshouldbeoperatedatdutycyclesof60%offullcapacityorlower,orequipmentdamagemayresult.


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

Reciprocating air compressors are available either as air-cooled or water-cooled in lubricated and non-lubricated configurations and provide a wide range of pressure and capacity selections. Generally, special consideration needs to be given in sizing air dryers for these compressors due to possible high discharge temperatures.

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

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

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

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

The centrifugal air compressor is an oil-free compressor by design. The oil-lubricated running gear is separated from the air by shaft seals and atmospheric vents.

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

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

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

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


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AIR SPRINGS

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

deck is possible when dock plates are unavailable.

The usefulness of air springs or actuators

didnt go unnoticed in the industrial machine industry, and it was clear they could offer

unique solutions for various applications. Air actuators have seen duty as shock absorbers,

linear actuators, vibration isolators and tensioners, to name a few examples. They can be used to

absorb shock in

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

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

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

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

ContiTech Industrial Air SpringsOffers Dual Functionality

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

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Application data needed for sizing a compact cylinder and choosing the best component: Operating psi, force required

(Force = Pressure x Piston Area) Stroke Preferred mounting, foot print Spring return or double acting

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COMPACT cylinders have been shortened relative to standard pneumatic cylinders. They may be up to 50% shorter than the normal cylinder, but still maintain the capacity to exert the same force as their larger counterparts. Important parameters for the proper selection of a compact cylinder can be broken up into general, dimensional, performance, material and features.

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

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

Compact CYLINDERS

Other items to consider: Ambient temperature Media temperature Environment Excessive loads other than

required axial force Load guiding (non-rotating)

requirement

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

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Pneumatic Actuators CYLINDERS

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

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

Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Unlike their hydraulic alternatives, the operating fluid in a pneumatic actuator is simply air, so leakage doesnt drip and contaminate surrounding areas.

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

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

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

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

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

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PNEUMATIC CYLINDER SELECTION:

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

When selecting an air cylinder, it is important to properly match the cylinder to the application, particularly in terms of required force. The theoretical force available in the actuator is the piston surface area multiplied by the supplied air pressure. Spring force must be subtracted from this value for single-acting cylinders. The actual force applied to the load will be 3 to 20% less due to pressure losses in the system.

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

d= 4A Stroke length is determined by the required travel of the machine element driven by the actuator. The final selection criterion is the cylinder mounting arrangement and the resulting configuration.

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

There are many factors such as system contamination, corrosion, minor leaks and wear that will affect the available air pressure and flow used to drive the actuator. An

actuator and fluid power system should be sized correctly so as not to waste energy, with a margin added to account for minor reductions in pressure and flow due to the factors listed above.

If the load connected to the rod is less than the resultant force, the piston and rod will extend and move the machine element. Reversing the directional control valve will provide compressed air to the retract port, allowing exhaust to escape the extend port, and the cylinder will return back to its home position.

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

Pressure and flow requirements of the actuators in a system must be taken into account when selecting these upstream system components to ensure desired performance. Undersized upstream components can cause a pneumatic actuator to perform poorly, or even make it unable to move its load at all. FPW

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Thereareseveralconsiderationswhenselectingthebesttypeofpneumaticcylinderslides.Theseinclude:

Loadcapacityrequired.Thetotalpayloadmustbecalculatedinordertostarttheselectionprocess.

Liferequiredfromtheslide.Thebearingsystemselectedwillhaveanimpactontheexpectedlifeoftheunitalongwiththerequiredspeedandpayload.

Speedrequired.Theslidespeedisacriticalcomponentincludingtheabilityoftheslidetohandlethekineticenergyastheloadstopsattheendoftravel.Cylindershockpads,cylindercushionsorshockabsorbersmayberequiredbasedontheloadandspeedoftheslide.

Deflectionneeded.Theamountofdeflectionwillvarybasedonthebearingsystemandthepayloadbeingcarried.Thisdeflectionwillaffectthepositionalaccuracyoftheslide.

Manymanufacturersofpneumaticcylinderslidesprovidespecificationandsizingsoftwaretoallowtheproperselectionofthesliderequiredforvariousapplications.

SPECIFYING CYLINDER SLIDES:

PNEUMATIC cylinderslides,androdlesscylinders(sometimesreferredtoasguidedcylinders)aredesignedtoprovidepowerandlinearmotionwhilesupportingaload.Stand-alonepneumaticcylindersaresuitableforprovidingpowerandmotion,butarenotdesignedtoprovidesupportforasideload.Mostofthesetypesofcylindershavenowayofholdingthepositionofthepistonrod,duetotherodsabilitytorotate.Pneumaticslidesprovidetheloadcapabilityandastable,non-rotatingplatformonwhichtomounttoolingorotheractuators.Thisisespeciallyimportantwhenacylinderismovinginahorizontaldirection,orwheresideloadisamajorissuecommoninautomationdevicesusedforpickingandplacingofparts.

Rodlesscylinderslidesarepopularchoiceswhenlongerdistancesoftravelarerequired,orwhentheoveralllengthmustbeminimizedduetospaceconstraints.

Typicalusesfortheseslidesincludeconveyorstops;partejectionandpositioning;openingandclosingsafetydoors,gatesorcurtains;andmulti-axisconfigurations.Inmanyoftheseapplications,theneedforsideloadcapacityandnon-rotatingcapabilityiscritical.

Theideaofapplyingaloadtoalinearactuatoriscommon,andthereareanumberoftypesofcylinderslidesthatcanbeusedfortheseapplications.Thefirstbasicstyleofpoweredslideiscommonlyknownasathrusterorcantilevertypeunit.Thistypeofguidedslideistypicallypoweredbyarod-stylepneumaticcylinder,whichisattachedtothebodyoftheslide,ormaybeintegraltotheslide.Ineithercase,thecylinderpistonrodisattachedtoatoolplateprovidingpowerandmotion.Thetoolplateissupportedbyabearingmechanism,andtogethertheyareabletocarryanyloadsthatareattached,ratherthantransferringtheloadtothecylinderrod.Thistypeofslideisdesignedtocarryanoverhungloadknownasacantileveredload.

Pneumatic cylinder slides/ RODLESS CYLINDERS

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

Another type of slide is a rodless slide. In this case, the bearing system is attached to the rodless cylinder directly on one or both sides of the cylinder. The cylinders piston is linked to a carriage mounted upon

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