Organizers of EMO Milano 2015 announced that Pier Luigi Streparava, President of Streparava S.p.A., has been named General Commissioner of the event. The global machine tool exhibition is scheduled to take place October 5-10, 2015 at the Fieramilano Exhibition Centre in Milan, Italy. The appointment took place during the general assembly of CECIMO, the European Association of the Machine Tool Industries.

Streparava, who is also President of the Italian-Chinese Chamber of Commerce,  will be promoting the event via a worldwide road show of conferences. He served EMO Milano in the same capacity in 2003 and 2009.

"Machines to build the future, cutting-edge solutions that give the possibility of achieving what mankind has imagined, and technologies on which the improvement of the quality of life depends on. This and much more will be EMO Milano 2015," stated Streparava in recalling the success of the last edition of EMO Milano. "EMO Milano 2009 was crowded by a total of 124,660 visitors, 41% coming from 99 countries other than Italy. Almost 400 credited journalists followed the event, where the main stars were the 1,400 exhibitors representing 39 countries".

EMO Milano 2015 is organized by EFIM-ENTE Fiere Italiane Macchine and promoted by UCIMU-SISTEMI Per Produrre, the Italian Machine Tools, Robots, and Automation Manufacturers’ Assn.

For more information, visit www.emo-milano.com.

Attendees of ConExpo and IFPE 2014 next March have another attraction awaiting them in Las Vegas. Three  air-powered hoists from J. D. Neuhaus— each providing a 50-ton lifting capacity — have been instrumental in the construction of the world’s largest observation wheel. Located at The Linq, Caesars Entertainment’s $550 million outdoor retail, dining, and entertainment district, the Las Vegas High Roller tops out at a height of 550 ft, comprises 28 viewing cabins capable of holding a total of 1,120 passengers.

Located at a temporary chain-fall platform suspended below the wheel central hub, the air-operated hoists were the most practical choice for this application — clean, safe, and much lighter and more compact than electromechanical hoists. Plus, the spring-applied, pressure-released design of the air hoists prevents loads from dropping unexpectedly, even if a compressed air line would be severed. Their 280 ft of cable fall were used to their full advantage in lifting equipment from ground level. These lifts included 18 temporary radial struts (each weighing 40 tons), together with transfer trusses of similar weights and all the individual outer rim segments of the completed wheel. These were paired with a 112 cable-locking assemblies initially assembled at 50% tension loads.

The temporary radial struts were installed to provide the accurate spacing of the individual wheel rim segments from the central hub unit during initial assembly. These were then sequentially replaced by the cable-locking assemblies, which — when fully tensioned — provided the radial spokes of the completed wheel assembly.

The Neuhaus hoists operate from a 6-bar air supply, offering lift capacities from ¼ to 100 tons. They incorporate a patented vane motor-brake system for low-maintenance operation with little wear. They also provide 100% duty ratings with unlimited duty cycles and are insensitive to outdoor operations involving dust, humidity, and temperatures ranging from –20 to 70°C.

The High Roller structure incorporates 3.5 million lb of steel, with the 112 cables forming the tensioned spokes of the structure having a combined total length of 25,256 ft; each cable boasts a breaking force of 550 tons.

Other vital statistics:

• In addition to its great height, the High Roller will offer an immersive pre-ride experience for its passengers on their journey from ticketing through the wheel house — complete with a lounge — to the wheel ride, which features unparalleled views of the Las Vegas Strip.

Ÿ• The wheel structure will boast 7.2 million lb of steel and 112 cables.

Ÿ• Each cable measures approximately 225 ft, for a combined total of 25,256 ft.

Ÿ• The High Roller will feature 28 spherical cabins, each capable of holding 40 people.

• Each cabin weighs approximately 44,000 lb and includes 300 ft² of glass.

Ÿ• Cabin windows are doubly curved and fabricated from four sheets of laminated glass.

• The cabins will also feature dynamic video and music shows that will fade away seamlessly to show the most impressive views of the Las Vegas valley.

• Fabrication of the wheel began in late 2011 and took place in several locations across the globe, including China, Japan, France, Sweden, Italy, Netherlands, Germany, Colorado, California and Las Vegas.

Ÿ• The High Roller will travel at 1 ft/sec and take roughly 30 min to make one full revolution.

• The wheel will be lit with more than 2,000 LEDs to create a customizable and visually stunning display.

Construction milestones:

• February 29, 2012 — Ground breaks on the construction of the High Roller.

• October 22, 2012 — Erection of the wheel structure begins.

• March 15, 2013 — The hub and spindle of the High Roller are completed.

• July 5, 2013 — The first section of the rim is installed.

• September 9, 2013 — The rim rim is completed with the installation of the 28th, and final, section.

• October 26, 2013 — The wheel structure is completed.

• November 2013 — Installation of 28 cabins began.

Click here to view pictures and more information about this newest Las Vegas attraction.

Going to IFPE? Don’t miss this

Many of us have already started making plans to attend IFPE, to be held March 4 to 8, 2014, in sunny Las Vegas. No wonder. IFPE is by far the largest fluid-power event in North America, and it only comes around once every three years. With this rare opportunity to see so much on the show floor, plus all the educational opportunities, it would probably be a good idea to plan on attending for several days if you want to experience everything. But to do everything, you’ll have to figure out how to be in two or more places at once — and that’s not even counting all the receptions, hospitality suites, and other entertainment events that will drain any remaining energy you might have.

We make a big deal about IFPE and its related events because it hits close to home for H&P readers. But IFPE is only part of what’s going on. There’s also ConExpo, the largest construction industry event held in North America. Those of us who have been around the block a few times can remember when IPE and ConExpo were separate events, with IFPE as a stand-alone event held at Chicago’s McCormick Place from 1988 to 2000. The National Fluid Power Association owns IFPE, and they partnered with the Association of Equipment Manufacturers to take over administration of IFPE and moved it to Las Vegas permanently starting with the 2002 event.

To get an idea of the size of ConExpo, consider that IFPE — again, the largest fluid-power event in North America by far — takes up most of the upper level of the Las Vegas Convention Center’s South Hall. ConExpo, on the other hand, takes up the South Hall’s lower level, the North Hall, the Central Hall, and much of the outdoor exhibit space.

IFPE’s affiliation with ConExpo causes some people to believe that IFPE is more a mobile hydraulics show than a fluid-power show because companies dealing primarily in pneumatics and industrial hydraulics aren’t as plentiful as they were when IFPE was a stand-alone event. As I see it, though, IFPE has more pneumatics exhibitors than any other show in North America that I know of — and loads of industrial hydraulics, too. Plus, the IFPE conference, which we’ll be previewing in our January issue, covers all aspects of fluid-power technology, not just mobile hydraulics.

And although ConExpo isn’t all about fluid power, dozens of fluid-power companies will be exhibiting there rather than — or in addition to — exhibiting at IFPE. Plus, the wide variety of machines and equipment on display should provide plenty of ideas to consider incorporating into your designs — even if pneumatics or industrial hydraulics is your main interest. Fluid power is fluid power, whether pneumatics, industrial hydraulics, or mobile hydraulics.

Installed in a specially constructed well, an 18-ton, 260‑kW floating-mount rod seal test bench is located at Trelleborg’s research and development center in Stuttgart, Germany. The machine is capable of simulating the patterns of movements and stresses faced by hydraulic rod seals in some of the most-demanding rod-seal applications, such as aircraft landing gear, injection-molding machines, and mining excavators. Holger Jordan, manager of Fluid Power Technology, says, “Our substantial investment in this test rig lets us offer our customers a unique facility to prove seals against ever-increasing development requirements.”

“The test bench is about simulating the real world as closely as possible in the laboratory,” adds Eric Seeling, the engineer responsible for its design. “The rig can perform long-term endurance and development tests, reproducing the effect on hydraulic rod seals of, for example, 25,000 landings of an aircraft or a million upstrokes on a press. In particular, it excels in aerospace applications where it can check parameters such as braking or lateral forces on landing gear and even simulate lifelike knocking caused by uneven runways.”

More than 35 years of testing experience went into the design of the test bench. The entire bench was installed in a concrete well to isolate vibrations from the surrounding building. The drive unit was set up in a separate room provide heat for the building from energy that otherwise would’ve been lost through emissions.

The test bench is suitable for seals from 4 to 16 in. diameter and can test a complete sealing configuration in a single test construction, replicating the pressure between the primary and secondary seals realistically. Traveling at speeds of up to 3.3 fps or frequencies to 10 Hz, it can generate movements and pressure patterns in sinus waves, trapezoidal forms, and even freely modeled patterns.

One of the test bench’s more novel features is a lateral force cylinder mounted at the bottom of the bench. Capable of exerting forces of up to 225 kN, it can place permanent radial loads on the seals or, depending on the stroke, exert dynamic loads. Another special feature is the ability to simulate different atmospheric temperatures between –76 and 194°F. Results can be fully documented, allowing customers to provide their clients with proof of performance related to prescribed parameters.

Visit www.tss.trelleborg.com for details about Trelleborg Sealing Solutions.

Most of us call them Popsicle sticks. More correctly, they’re called ice-pop sticks. But whatever you call them, John Lewis Industries Ltd., La Tuque, Canada, has been making ice-cream sticks (as they call them) since 1920 and now produces more than 26 million of them a day. Not surprisingly, the company also produces tongue depressors for the medical industry and coffee stirrers and wooden sticks for hobbies and crafts. Roughly 85% of Lewis’s output is exported to countries around the world.

The sticks are peeled from Eastern Canadian white birch, which is used primarily for its color, rigidity, and neutrality of smell and taste. John Lewis Industries is a stickler for environmental responsibility. The company draws upon sustainable forestry certified by the Forest Stewardship Council. And, of course, it has an eye on energy conservation. Bark from the harvested trees is burned to generate steam for the plant’s use.

Always looking for ways to conserve energy, company officials launched an optimization project for the production process. Following initial studies, they consulted with energy-efficiency specialists from Bosch Rexroth to take a close look at the power unit for the hydraulically driven axes in the plant’s wood-receiving station.

It ain’t broke, but fix it

Incoming timber arrives at the plant as 8 to 10-ft logs that are routed to a receiving station, where an automatic lift device raises the logs and moves them into a peeling mill. The peeling mill strips thin sections of wood from the log, and the peeled wood undergoes further processing. If any obstruction occurs in the receiving station, an operator uses a hydraulic crane to free the jam. Hydraulics for the crane are fed by the same hydraulic power unit (HPU) that serves the receiving station. This HPU was the focus of the project.

Because this is such a high-production operation, interruptions are not an option. Rodney Trail, of Bosch Rexroth Canada, explained that to ensure the operator could always respond quickly to carry out the unjamming procedure — which is initiated manually — designers originally specified a fixed-displacement pump running at full speed. This ensured that maximum hydraulic flow was available to give the hydraulic quick response. When full power wasn’t needed, excess flow was routed to tank. At full load, the HPU required 20 kW of power and 12 kW even at partial load.

Specialists at Rexroth determined that using a fixed-displacement pump driven by a variable-speed electric motor could save substantial energy without affecting system speed, power, or response. Trail said his team recommended using Bosch Rexroth’s Sytronix SvP7000 variable-speed pump drive. Bosch Rexroth’s IndraDrive intelligent control reduces the pump’s rotational speed during idling phases or when operating at partial load to deliver just the amount of flow actually called for by the crane operator.

The IndraDrive runs the hydraulic pump at speeds from 0 to 2,700 rpm, which generate flows to 60 lpm. The motor-pump drive also closed-loop pressure control up to 100 bar and maintains it within about 0.3 bar.

This conversion brought about instant success. When running at partial load, the hydraulic power unit now uses just 2 kW — a 70% energy saving. Trail explained that the conversion itself was fairly easy and uncomplicated. “Predefined functions and open interfaces for command-level communications simplify integration, even into preexisting systems. Users need not carry out any extensive programming. They need only assign parameters to the predefined regulators.”

It’s quieter, too

Energy is one factor but an acceptable working environment for the employees is just as important. “We are not talking just about energy savings, but also about considerable noise reduction and better system response,” explained Stéphane Pronovost, project manager at John Lewis Industries and responsible for rebuilding the system. That’s because the Sytronix reduces, on the one hand, average noise emissions by up to 20 dB — and without any additional noise abatement measures. The rapid response to changes in flow and pressure requirements give the crane more-precise movement and makes it easier to operate.

Set for the future

In addition, Sytronix reduces the amount of cooling required since the hydraulic fluid heats up less than in the past. This both extends the service life of the hydraulic fluid and further reduces energy requirements. “I hope that this technology will become the industry standard for all hydraulic power units in the future,” Pronovost stressed. John Lewis Industries is making its contribution and is even now examining the feasibility of converting another power plant.

For more information on Bosch Rexroth’s Sytronix hydraulic motor-pump drives, visit bit.ly/190RzKt.

You’ll find some of the largest fluid circuit lines in the world at refineries and large-scale chemical processing plants, where miles of large-diameter tubing is commonplace. Because it is clean, safe, compact, and powerful, pneumatics is widely used to actuate large valves in these applications. Lehigh Fluid Power, Lambertville, N. J., provides a wide variety of cylinders for use in valve actuators.

Lehigh’s VAC cylinder line comes in carbon and stainless steel, and a lightweight version has a barrel made of lightweight composite. VAC cylinders are available in standard bores from 8 to 16 in. All use Lehigh’s Miraclube feature, a system that self-lubricates the rod and piston bearings with a nontoxic lubricant that will not attack seals or fuse seals to the tube ID if the piston remains in one position for an extended length of time.

For more information on Lehigh Fluid Power’s VAC cylinders, call (800) 257-9515 or visit lehighfluidpower.com.

Whether they use a piston or a bladder, accumulators are all about precharge pressure. When sizing an accumulator, specifying the correct volume and precharge pressure can mean the difference between a system that runs smoothly and efficiently, or one that is plagued with problems. Mac Stuhler, vice president at Control Products Inc., East Hanover, N. J., explained that monitoring the precharge pressure of a bladder accumulator is fairly straightforward: install a pressure transducer to detect the pressure of the precharge gas in the bladder.

Stuhler revealed that piston accumulators pose a different scenario. Because piston seals are dynamic, they are subject to wear and eventually will leak. This can cause the piston to drift, so even though a pressure transducer may indicate the correct pressure, the piston may not be where it should based on the pressure. If the piston is too close to the end cap, then a sudden increase in system pressure could cause the piston to slam into the end cap — certainly a dangerous situation. For this reason, designers often specify an accumulator with a longer stroke than necessary to provide extra length in case the piston has drifted.

To address these challenges, Control Products introduced three sensors that detect the absolute position of pistons in accumulators (and hydraulic cylinders, too). Control Products’ SL Series sensors use a stainless-steel cable that enters the accumulator through an SAE Size 8 fluid port and attaches to a ⁷/₁₆-20 hole machined into the piston. The cable is connected to an LVDT that provides a continuous and absolute analog or digital output signal indicative of the piston location using noncontact sensing technology.

Stuhler said the SL’s sensor works on the gas or fluid side of the piston and alleviates issues associated with rod-type position sensors.

The SL sensor is available in three standard sizes:

• the SL390 accommodates strokes to 1 m;
• the SL1200 measures strokes to 3 m; and
• the SL1400 handles strokes to 7 m.

For more information, call Control Products at (973) 887-9400, email sales@cpi-nj.com, or visit www.cpi-nj.com.

Pump architecture and its control system are organized in view of the latest technology, but also with a healthy regard for technological limitations. The system configuration places a control computer directly on the pump housing. This computer provides a high degree of local control.

Any knowledgeable bus technologist will admit that tight servoloops cannot be reliably closed by sending feedback and error signals over the network. The problem is the uncertainty of data-transmission timing and the resulting time delays. The industry refers to this problem as bus latency. It is worthwhile to understand time limitations of buses

Bus irregularities

To use the jargon of bus experts, some buses are not deterministic. This means the time between, say, the sending of a command, and the acknowledgement that the system has responded, does not occur with repeatable time lag, even though the controlled machine has precisely the same response every time. Because of other data traffic on the bus, the bus itself inserts randomness to the data exchange process.

The Internet is an example. You can visit the same Web site each day for five consecutive days, but the time it takes for your screen to redisplay will vary from day to day. It may exchange exactly the same amount of data each time, and your computer may be exactly the same. However, other traffic on the network is random, so you see a variation in the response time of the Internet.

Field buses that will eventually be connected to our pump can be designed to have a degree of determinism. In bus-speak, determinism means that there is a fixed and known amount of time delay between communication events. Buses that use, for example, token-ring passing to gain access to the bus can have very repeatable response times from trial to trial. And scan times are reaching the low millisecond range — a noteworthy accomplishment. In spite of this, vendors and supporters recognize that absolute determinism is not possible. Perhaps more importantly, they also realize that a very-low delay time cannot be achieved, so they recommend that all tight servoloops be closed at the device. Other bus architectures and access strategies suffer from random variations between repeated events with the randomness caused by other bus traffic.

In our case, the device is the pump and all of its immediate, integrally mounted peripheral electronic gear. Displacement and pressure must be controlled, among other things, and servoloop update times must be no more than 1 or 2 msec to provide the ultimate in pump performance. To do and expect less is to relegate the control system to a role that is unworthy of its investment cost. The dedicated local processor — which the bus industry calls distributed control — will ensure that response and performance will be the best that the hardware can deliver. Sending the data back to a central processor to close the servoloops would jeopardize response and performance.

Pump performance profiles

The flexibility designed into an electrohydraulic pump offers the maximum of utility to the user. The versatility is mechanized through computer software to control the hardware already described. With the right software, several conventional pump configurations can be achieved:

• simple variable displacement,

• pressure compensation,

• power limiting, and

• load sensing (output flow control).

The conventional means for implementing these basic pump functions has been through sensing, feedback, and control in hydromechanical hardware. This will continue to be done well into the future. However, for the ultimate in versatility and control, electrohydraulic pumps will gain increased acceptance. The need for users to “talk to” and “listen to” all types of mechanical devices (including pumps) will lead to the demand for communication interfaces. This will also boost the demand for sensors and controls.

Simple displacement control

Pump-displacement control begins with the servo or proportional valve whose hydraulic output connects to the pump’s servo-stroking pistons, as shown in Figure 1. The pump-stroking pistons move to change the cam angle and, thus, change the displacement. An amplifier appropriate for the valve coil — either torque motor or proportional solenoid — electrically drives the valve.

The input to the amplifier comes from the local computer, or more precisely, from a digital-to-analog converter (d/a) that is connected to the local computer. Meanwhile, a swashplate angle transducer, HD in Figure 1, sends its signal to the computer through an analog-to-digital converter (a/d).

The a/d converter receives output from the angle transducer, converts the signal to a parallel digital value, and “places” it on the local computer chip’s internal parallel bus. (This bus is not to be confused with the serial-communications bus that will carry signals to and from the pump over the entire factory network.) As it resides on the computer bus, the value of the angular position is available to the programmer, who must provide the correct computer code to acquire it.

At this point, the programmer must know the physical port to which the angular position signal is connected in order to read the angular value. The programmer must also know where the command signal is coming from. Here is where things really get interesting. Sometimes the command will be internally generated from other control software. Other times, it will “come down the factory network bus.”

Control in mobile applications

For example, in a mobile machine — where the pump stroke may be controlled by an operator’s joystick — the command would arrive at the pump through the vehicle’s serial fieldbus (CAN, for example). On the other hand, if the pump is operating in start-up mode, there may be a software command profile that gradually brings the displacement up to some predetermined value. In either event, the programmer must know the mode of operation and, if applicable, to which port the command is connected.

For the mobile application, the command would appear on a digital input to the local computer, as handed off from the serial-bus interface. The program would:

1. read the data at the port for the command,

2. read the port for the swashplate angle transducer,

3. calculate the difference between the two, and

4. output this difference (the error) to the port that feeds the servo or proportional amplifier.

This process closes the servoloop on pump displacement. A command could be sent from the operator’s joystick, and the pump would take on the commensurate displacement. If a programmed displacement changes, such as with the scenario just described, a predetermined set of displacement values would be established — a data array. Think of this as a column of numbers stored in the local computer memory.

Upon receiving the trigger to start, the computer would read the first number in the array and use it as the displacement command. After a few milliseconds, the program would go to the array again, but read the next value, use that as the command, and so on, until reaching the end of the array. There may be as few as a half dozen different values in the array, or there could be hundreds. The more values, the smaller each command step size, and the smoother the start-up. In that way, the displacement would follow the desired path in going from the initial value to the final value. It is not a great stretch to realize that the scenario for the joystick command and the command profile are very similar. The only real difference is where the local computer looks to find the next command value.

Commanding from memory

How does the command profile get into the local computer memory? There are two possibilities: First, if the profile is known when the pump is manufactured, it can be loaded as a part of the final test on the pump. If it’s not known until application, the pump would be installed and connected to the factory or vehicle serial-communication bus.

During a configuration process, all the pertinent data involving the pump (transducers, math models for diagnostics, and all special start-up profiles) would be entered into a master computer remote from the pump computer. At the appropriate moment during commissioning, all the pump’s parameters would be downloaded from the master computer to the pump computer. All values would reside in local memory and wait for their unique command signal.

This lets the pump be operated by a joystick or a command profile. When the master computer sends a mode signal to the pump, one value would signal the computer to look to the joystick, the other value would signal it to look to the stored command profile.

Pressure compensation

Using the mode signal concept, the pump can be made to perform as a conventional pressure-compensated pump. In this mode, if the pressure is lower than a setpoint or commanded value, the displacement increases. A command signal is sent to the controller, and if the pressure measured by the output pressure transducer is less than the command value, the error voltage is then sent to the d/a converter, then to the servo or proportional amplifier, which causes the displacement to increase. Figure 2 is an analog-style, block diagram of the pressure-control system showing the hardware and software functions as if they were all actual hardware.

Note the feedback loop within a feedback loop. The pressure loop is “wrapped around” the displacement-control loop. It’s not a disturbing situation, but it creates a problem that may not be immediately apparent: the control law for the system does not produce a pressure-feedback signal equal to the command signal. Error exists in the pressure control that is caused by the displacement-feedback loop.

To understand this problem, consider the situation where the system is operating in steady state: constant output pressure and shaft speed, and the load flow is constant and moving some load. This situation requires the pump cam angle to be constant. If the cam angle is stationary, then the servo or proportional valve must be centered. With the valve centered, the current must be zero — meaning that the cam angle error signal in Figure 2 also must be zero:

ε_CA = 0 = (A_P× ε_P) – ƒ_CA,

where ε_CA = cam angle error, A_P = gain of the pressure error amplifier (software), ε_P = pressure error as indicated in Figure 2, and ƒ_CA = feedback signal from the cam angle transducer.

But pressure error can be expressed as:

ε_P = P_C× P_FB,

which can be substituted into the first equation:

ε_CA = 0 = (A_P× P_C– A_P× P_FB) – ƒ_CA,

Solving for the feedback pressure, which is a measure of the actual output pressure, we get:

P_FB = P_C– ƒ_CA/A_P,

which is the important form of the final steady-state control law.

First, the preferred control law would be one with the ƒ_CA term equal to zero. Therefore, the actual (feedback) pressure would be the same as the commanded pressure. However, because the ƒ_CA term is not zero, it causes the actual output pressure to be less than the commanded pressure, which may or may not be tolerable.

The system can be recalibrated so that the commanded pressure always exceeds the actual pressure, and the command from the operator can be rescaled to be essentially invisible to the operator. Also, the dynamic response of the system may be enhanced using the configuration of Figure 2. However, just as with hydromechanical pressure compensation, the load flow affects output pressure, no matter how much the program changes with the command signal. Again, this may or may not be tolerable. The performance should not be worse than with a conventional pressure-compensated pump.

Also note that the cam-angle feedback signal is divided by the gain of the pressure-error amplifier. So as the gain increases, the error contribution diminishes. As with all feedback systems, too high a gain forces the system into sustained oscillations.

Pneumatics is routinely used in medical devices due to the safety and cleanliness of compressed air. Applications range from driving small and simple handheld tools to powering large and complex operating-room equipment.

Suppliers like Pneumadyne, Plymouth, Minn., make a range of miniature pneumatic valves, fittings, and controls for a wide variety of medical hardware. The company’s standard components are generally the first choice when medical-device manufacturers are assembling systems — provided they suit the application requirements. Benefits include wide availability, quick delivery, and economical pricing. The range of standard offerings includes:

• Directional-control valves in a variety of porting sizes and configurations.

• Miniature regulators that precisely control air pressure and are suited for limited-space applications.

• Stainless-steel valves and fittings that withstand corrosive environments.

• Oxygen-clean pneumatic valves and fittings that are free of particulates, oil, grease, and other contaminants.

Often, however, off-the-shelf products don’t quite meet an OEM’s requirements when integrating pneumatics into medical equipment. For that reason, custom-designed components and controls are found in a wide variety of medical devices.

In many cases, Pneumadyne engineers will consolidate a number of components into a single, custom-built manifold system or valve block — without compromising performance. Integrating components offers numerous benefits, such as eliminating potential leak points, reducing the opportunity for contamination, and simplifying system assembly. Last but not least, it improves the appearance of a circuit.

Here’s a look at two custom products that the company recently developed.

Valve assembly

A medical-equipment manufacturer asked Pneumadyne’s engineers to evaluate a new trauma device that was under development. The medical OEM’s design team had prototyped the pneumatic system using discrete components from various manufacturers. But the design needed several improvements.

Among the application requirements:

• The pneumatic circuit had to fit inside the customer’s existing equipment housing.

• Decrease the time required to assemble and install the circuit.

• Meet specific flow and pressure requirements at a pump pressure of 7 psi.

• Provide pressure-sensing feedback to the host computer.

• Eliminate potential leak points.

The Pneumadyne’s engineering team redesigned the circuit into a block assembly that eliminated 25 individual components. The device included three pressure transducers that provide an electronic interface for the measurement of system pressure; push-to-connect fittings that simplify tubing connections and system installation; a built-in, quick-reaction air reservoir; and four solenoid valves to control cylinders and other functions within the circuit.

The design also included a custom, double-acting rolling diaphragm cylinder with integral position feedback. The cylinder had to function without “stiction” or hesitation at a pressure differential of only 1.5 psi.

The block assembly met the application requirements, eliminated numerous potential leak points, and reduced the amount of time needed to plumb the pneumatic circuit.

3-in-1 manifold

Another equipment manufacturer faced the challenge of reducing the size of a pneumatic system to fit the space constraints imposed by operating-room equipment that had already been designed. Complicating matters, several components within the device had to withstand autoclaving sterilization.

Pneumadyne engineers sought to combine the functions of several individual operatory devices into a single package. The goal was to reduce the space needed for three separate pneumatic circuits while meeting specific flow and pressure demands.

To solve the problem, the engineers developed an integrated manifold block that houses the three separate circuits and meets the space constraints of the customer’s equipment. This multifunction assembly, in turn, let the customer replace several devices within the operatory.

The design included:

• A precision regulator preset at 2 psi controls pressure in one circuit.

• A regulator preset at 7.5 psi supplies pressure to a water chamber.

• A valve housed within a plastic cap controls water flow.

• Four pressure transducers measure system flow and pressure.

• Five oxygen-cleaned solenoid valves.

• Push-to-connect fittings that ease tubing connection and system installation.

• Two relief valves to vent overpressure.

Special tests ensured that the device met the required flow and pressure specifications.

For more information on Pneumadyne’s pneumatic products, visit www.pneumadyne.com.

In the logging industry, ever-higher levels of automation have increased log-harvesting productivity. One case in point is the Scorpion, an eight-wheeled harvester by Finnish manufacturer Ponsse Vieremä. The Scorpion processes standing timber into cut-to-length logs ready for transport from the forest to a finishing mill. Its frame is comprised of three parts linked by rotating joints. Front and rear frames are each linked to the center cab frame by these joints. The middle frame is kept level along its longitudinal axis by hydraulics. In fact, a leading feature of the Scorpion harvester is its stabilized design, which comes from its eight wheels and active stabilization system.

The Scorpion’s front and rear frames tilt according to the contours of the terrain. Its eight wheels may be tires or paired in with treads (front and rear, right and left) for traction in extremely rough terrain and harsh winter weather. The vehicle’s operator sits on the centerline of the vehicle in an ergonomically designed cab. The frame design keeps the pivoting point as low as possible and minimizes tilting, preventing the operator from swaying sideways.

Once a tree is selected for harvesting, the operator maneuvers the crane so that the jaws on the Scorpion’s harvesting head grip the tree’s trunk as a saw blade cuts the tree at its base. The log is then pivoted to a horizontal position, where hydraulic motors rotate wheels that pull the tree trunk through the harvesting head. As the trunk passes through the harvesting head, it strips off the tree’s branches and cuts the log to a predetermined length. After the first section is cut, the remaining length of tree trunk passes through the harvesting head, is stripped of its branches, and is cut to length. This continues until the entire usable length of the tree is cut, then the operator moves on to the next tree.

Hydraulics gives Scorpion its sting

Handling the heavy mass of the tree trunks requires an incredible range of motion and strength, often in demanding weather conditions. Not surprisingly, hydraulics is the only form of power transmission that can deliver this type of performance. Mounted at the end of the Scorpion’s crane is Ponsse’s H7 harvester head. Once properly positioned, the agile H7’s jaws encircle and clutch the trunk of the tree to be harvested. The harvester head then proceeds with its stripping and cutting operations.

A considerable amount of torsional movement is required of hoses that route pressurized hydraulic fluid between the crane arm and harvesting head. Consequently, hydraulic hoses must be mounted on swivels to prevent twisting hoses’ reinforcing construction, which would cause premature hose failure. In extreme cases, torque transmitted through the hose can actually loosen its end fitting.

The Scorpion operates at pressures reaching 4,350 psi. At this pressure, traditional ball-bearing hose swivels can wear out prematurely. For this reason, after several years of testing, Ponsse engineers selected swivels of a different design: ball-less swivels from Taimi Hydraulics in Canada.

Swinging into swivels

Swivels accommodate rotational movement of hydraulic machine parts. Without them, even the best of hose assemblies would fail prematurely from repeated twisting. Given all the complex movements required of the Scorpion, torsional loads on its hydraulic hoses would quickly fatigue their reinforcement if not compensated for by swivels.

Ball-bearing swivels are effective when hydraulic operating pressures were 3,000 psi or lower. At higher pressures, however, a different approach to swivel design became necessary, which is why Ponsse considered using Taimi’s ball-less swivels.

Taimi’s swivels are more costly than the ball-bearing version, but Ponsse personnel believed that the potential benefits far outweighed the cost differential. In order to be sure they were making the right move, Ponsse officials tested the ball-less swivels for four years in Finland and in the United States before deciding to use them on new machines they build.

Protection from pressure spikes

A shank-nut assembly is the key to the ball-less swivel design’s effectiveness. The long span of the shank allows for optimal load distribution. The shank is inserted through a seal assembly and into the nut. A thrust washer, made of a self-lubricating polymer, provides low friction for torsional movement and also provides shock-absorption properties. The nut then fastens the rotating shank securely to a housing, block or manifold. The swivel’s sealing characteristics are achieved in two stages: by contact under pressure between the thrust washer and the nut, and by two sets of oversized Viton O-rings and back-ups. A key benefit of this design is high wear resistance in the field.

Ball-bearing swivels have a lower load capacity because of the small contact area between the balls and their races — thin arcs support the swivel’s entire load. Consequently, both balls and races can wear out quickly, thereby increasing the torque needed for rotation and eventually hindering the free motion of the swivel. This, in turn, can lead to leaks and, ultimately, to swivel and hose failure. Similarly, side loads applied to ball bearing swivels reduces life of the component. In the ball-less design, the load on the swivel is applied more uniformly around its circumference, thus reducing the effect on life of the swivel.

Another valuable characteristic of Taimi’s ball-less swivels is their pressure spike protection (PSP) feature, which dampens pressure spikes. The swivel acts as the hydraulic equivalent of a voltage surge protector used with electronic equipment by keeping its components from being damaged in the event of an energy surge. When a pressure spike arises in a hydraulic line, a thrust washer made of engineered plastic prevents the surge of energy from reaching the swivel’s seals.

The ball-less swivel design also prevents the swivel from pulling apart under load, thus reducing leaks, failures, and downtime. In the ball-bearing swivel, gradual wear to the bearings and races will result in increased play between mating components. This play can be the beginnings of a leak, but when the wear becomes excessive a hydraulic pressure peak or strong pull on the hose may well disconnect it. The result is a safety hazard, a fluid leak, and costly downtime.

Successful results

Since Ponsse began specifying PSP swivels into its original equipment, the swivels don’t leak, the machines perform better, stay cleaner, operate with less downtime, and spill less oil into the environment. The ball-less swivels do not pull apart, significantly reducing the risk of oil spills. Because they do not use ball bearings, they will not seize, thereby increasing hose life. Ponsse is also using ball-less swivel cartridges, which offer the same benefits as in-line swivels. However, they can be directly inserted into a manifold, so the size, length, and cost of an assembly are significantly reduced.

Whether in the forestry industry or any other, hydraulic systems with hoses that must undergo torsional movement need swivels to prevent transmitting torsion to the hoses. Ball-bearing swivels serve the needs of many applications, but when low leakage and longer life of the swivel and hose are important — especially in systems operating at higher pressure and exhibiting pressure spikes — ball-less swivels can be a wise investment in better machine performance.

Ponsse (www.ponsse.com) equipment is available in North America from its facility in Rhinelander, Wis. Visit bit.ly/18i0Kma to see a video of the Scorpion in action, and go to bit.ly/18i0SlA for a video that shows the flexibility of Ponsse equipment afforded by Taimi’s swivels.

Sebastien Tremblay is Managing Director at Taimi Hydraulics, St. Prime, Canada. For more information, call (418) 686-6868, ext. 707, or visit www.taimi.ca.

When applications involve linear motion, high speed, and moderate loads, air cylinders are often the first choice to provide the actuation. Compressed air is available as a utility at almost every industrial facility, and economical air cylinders can be obtained from many manufacturers. One of the most fundamental
fluid-power components, cylinders have evolved into an almost endless array of configurations, sizes, and special designs. Their versatility not only makes more innovative designs possible, but also makes a reality of many linear applications that would not be practical or possible without cylinders.

Cylinders are simple devices, and calculating their theoretical force output is fairly straightforward. However, sizing a cylinder properly for a real-world application is more complex. Undersizing, for example, is a common mistake that results in sluggish performance and cycling problems in automated equipment. Oversizing a cylinder wastes energy by using more air than is necessary. However, by following a few simple guidelines, you can quickly learn how to determine the right cylinder to fit their specific needs.

Calculate the force — The theoretical force output of a cylinder is the product of the air pressure applied and usable piston area exposed to it,

F = P× A,

where F = force in lb, P = supply pressure in psi, and A = piston area in in.²

For example, a cylinder with a 1½-in. bore supplied with 80-psi air would generate:

F = 80 × π(0.75)²

F = 141 lb.

Note that area is fixed once the cylinder is selected and installed. Pressure can be varied, but only over a limited range. Therefore, it behooves the designer to calculate force, and, hence, area, very carefully early in the project. Also note that the formula calculates the theoretical force output. Several factors can and will lower it in a real application. Keep the following issues in mind whenever you size a cylinder.

Account for internal friction — Internal friction prevents a cylinder from achieving its theoretical output force. This friction is produced by piston and rod seals, bushings, wear bands, and other load-support and sealing components. A common general rule is to allow 5 to 10-psi additional input pressure to overcome internal friction, depending on the cylinder’s design and bore. Cylinders with side load, misalignment, or specialty features may have even higher internal friction. A cylinder converts pressure to linear force, so considerable side loads and bending moments should be avoided or accommodated separately.

Consider the annular area — For calculations where a load will be moved during the cylinder’s return stroke, the cross-sectional area of the piston rod must be subtracted from the piston surface area. This is known as the annular area. The previous example used the full-bore area, but if you are moving a load on the return stroke, or using a cylinder with a rod at both ends, then the annular area must be used to calculate the usable piston area. (Rodless cylinders, however, have the full-bore area available on both faces of the piston, which eliminates the annular area.)

Know the actual operating pressure — Although a compressor may produce a specified pressure, the pressure at the cylinder can be much lower due to flow restrictions in compressed-air lines and air consumption by other devices in the air-supply network. An air system that runs at 100 psi may drop to 80 psi or less during peak air-usage times of the working day.

Know the true load — Unless you are lifting a load vertically, it can be somewhat difficult to determine the true load because of external friction. Even if a load is lifted vertically, if it is guided in any way, there will be additional friction. Calculating the force loss due to sliding friction must include friction factor:

Ff = F_p× f_c,

where F_f = friction force, lb; F_p = force perpendicular to the sliding surface, lb; and f_c = the coefficient of friction.

If the sliding surface is level, the perpendicular force is the object’s weight. If the sliding surface is inclined, the perpendicular force is the product of the cosine of the incline angle and the object’s weight.

Extensive information is available that documents coefficients of friction for various materials, but small variances in this number can make large differences in the required force. If you are sizing a cylinder for an existing application, try to physically measure the required force. If the application is new, do as much physical experimenting as possible to verify any calculated numbers you use.

Determine speed requirements — After summing all the forces, the remaining (net) force is what causes motion. Acceleration of the load will be equal to the net force divided by the total mass being moved,

F_n = m× a

Unfortunately, it’s usually not this simple. Coefficient of friction often changes with speed. Furthermore, if net force is low, the cylinder may exhibit stick-slip operation, sometimes called stiction. Stiction occurs when force from pressure is great enough to overcome static friction and begin moving the cylinder’s piston. Once the piston starts moving, dynamic friction comes into play. If static friction exceeds dynamic friction, the piston may suddenly stop when moving at very low speed because static friction has taken over. As pressure builds, the piston again overcomes static friction force, and the piston lurches ahead. This start-stop motion can occur repeatedly and rapidly, resulting in a condition sometimes called “chatter.” Correcting the condition requires redesigning some aspect of the assembly, such as higher pressure or a larger bore. If these solutions are not possible, then seal and bearing materials with a lower coefficient of friction or additional lubrication may be called for.

Ensure adequate piping — The compressed air must reach the cylinder’s piston quickly to build the pressure that will produce the force to move the load. Lines sized too small and with too many bends, turns, and restrictions will restrict airflow, causing sluggish operation and low force or torque from the actuator. Sizing lines and components too large will increase the volume of air that must be pressurized, increasing system response time.

A helpful analogy is that one person may be able to push a car at 1 mph, and two people may be able to push it at 2 mph. But 100 people cannot push a car at 100 mph. The reason they can’t is because they reach their terminal velocity. Although the 100 people have more than enough strength to push the car, they can’t move more than their own maximum (terminal) speed. Compressed air is subject to the same limitations. If air can’t be delivered through the system quickly enough, then the pressure (force) at the cylinder will not reach that required to move the load. This potential problem is a result of inadequately sized components or an unbalanced system, not just too small a cylinder.

Consider the angles — If the cylinder in an application deals with linkages or has a force transfer angle or other pivoting member, allow for force losses in those angles. The force actually transmitted to the system is equal to the net force multiplied by the sine of the transfer angle:

F_t = F_n× sinθ

where F_t= force applied to the load, F_n = net force, and θ = the transfer angle.

The force absorbed by the pivot is equal to the net force multiplied by the cosine of the transfer angle:

F_t = F_n× cosθ

When the transfer angle is greater than 135° or less than 45°, more cylinder force is acting against the pivot than is being transmitted to the application. Transfer angles greater than 150° and less than 30° transfer less than half the cylinder force to the application, so they should be avoided. In these cases, a different mechanical arrangement or a rotary actuator could be used.

Plan for the future — Specifying cylinders with nothing in reserve does not allow any leeway for future modifications to the application. Designing applications with some capacity held in reserve can allow for continued operation when a machine has been in service for a significant time (which may have increased friction) or when slight increases in product requirements or unforeseen force losses occur. For example, new pneumatic equipment installed in the facility may affect the available air pressure at your application. You can always add a regulator to reduce the pressure and output force, but it is much more difficult to increase force.

Account for kinetic energy — The load is moving, but what will stop it? Cylinders have some ability to absorb kinetic energy, but their primary purpose is to convert pressure to linear force. Installing a shock absorber can transform a potentially destructive moving mass into a good application.

Be sure to test — Trying to size a cylinder mathematically to an application without any testing can be an expensive mistake. Once an application has been built, it can be quite costly to make changes to accommodate a larger-bore cylinder and may require redesigning an entire machine to accommodate additional space that may be required. If it turns out that more force or a different shape of cylinder is required, a tandem cylinder may provide a solution. Tandem cylinders have two pistons mounted to a common rod, so it provides greater force from a small bore, but at the expense of a longer length.

Information for this article was excerpted from material by Numatics Inc., Mt. Pleasant, Tenn.; Clippard Industrial Laboratory, Cincinnati; Peninsular Inc., Roseville, Mich.; and Bimba Mfg., University Park, Ill.

Hydraulic systems often incorporate pressure transducers to monitor for safety as well as optimize system performance using closed-loop feedback. For instance, pressure transducers within a hydraulic control system can ensure that a heavy load won’t tip over a forklift, monitor trash-compactor performance, control hydraulic pumps on oil rigs, or ensure accurate performance of aircraft landing gear.  Although hydraulic applications vary greatly in terms of safety and precision, the same principles apply to protect pressure transducers against hydraulic overpressure events, fatigue, and environmental conditions.

Pressure Spikes Induce Transducer Failure

Pressure transducers can be specified to work under steady-state or pulsation conditions. A typical hydraulic system, whether stationary or mobile, operates from 0 to 500 psi (35 bar) to 10,000 psi (700 bar). Most pressure transducers are specified with a proof pressure or overpressure specification; therefore, transducers should perform within specification at two times the rated pressure (such as 6,000 psi for a 3,000-psi pressure transducer).

For some benign applications, pressure transducers can be dropped into a hydraulic system and operate accurately without modification. In other cases, pressure events will far exceed the transducer’s normal operating pressure limits. For example, if a local hardware store’s hydraulic trash compactor has a block of concrete stuck under the lip of the moving body, pressure pulsations sent to the pressure transducer may extend far beyond the hydraulic system’s normal operating pressure. Such a pressure event can be five times the transducer’s rated pressure, leading to failures in standard transducers. In another scenario, if a forklift operator picks up a full load on the forks and lowers it to the ground, the forks could bottom out and send a pressure spike through the hydraulic lines. When the spike reaches the transducer, it’s likely to exceed rated pressures, again damaging transducer failure.

Fast-acting valves also create pressure transients. For instance, the pressure event from a transducer located close to an opening and closing valve will create surges downstream from the valve. Pressure surges can cause a pressure transducer to fail by deforming the diaphragm or breaking the sensing elements above it. Possible ramifications include cracked ceramic diaphragms, shifting of oil-filled units, and wire bonds lifting off of strain gauges.  

Icing also produces situations similar to pressure transients. If water becomes trapped within an unpressurized hydraulic system, it can freeze in cold ambient conditions and generate a simulated pressure of 1,500 psi. A pressure transducer doesn’t recognize the difference between pressure and ice, and will fail after long-term exposure to these conditions.

High Pressure-Resistant Transducers

One way to protect pressure transducers against pressure spikes or rapid pressure changes is to add a restrictor plug (snubber) inside or outside of the process connection. The snubber serves to dampen spikes and surges on the pressure transducer, Figure 1. Internal snubbers reduce the transmitter’s overall height, whereas external snubbers facilitate cleaning of hydraulic systems, which are prone to collect contamination. 

Another possibility is to increase the pressure transducer’s proof pressure. Advances in signal processing now enable manufacturers to use thicker diaphragms when manufacturing the internal body of units, which boosts proof pressure for the same measurement range with minimal losses in performance.  Rather than lose resolution by increasing the device’s measurement range, the transducer manufacturer can calibrate the same pressure range with a higher proof pressure. 

The proof-pressure solution is ideal for icing issues. With snubbers, it’s possible to trap water within the transducer. On the other hand, an open cavity with higher proof pressure than the freezing-induced maximum pressure exerted on the diaphragm would be more likely to survive. 

With the exception of a flush-diaphragm transducer, all pressure transducers have a cavity that transmits fluid pressure to a diaphragm. A snubber can be installed inside that cavity with a smaller inside diameter to dampen a pressure spike as it travels through the hydraulic to the transducer. Instead of the pressure wave shocking the diaphragm, it hits the face of the snubber and slowly feeds the liquid through the hole. 

Technology Considerations

The type of technology chosen for hydraulic pressure transducers depends heavily on the nature of the application and operating pressures. For example, a pressure transducer with a capacitive or thick-film ceramic diaphragm, Figure 2, is typically specified up to 400 bar with 1½ times of rated pressure for steady-state applications. This transducer will fail in dynamic and pulsation applications due to fatigue, because ceramics perform poorly under tension.

Similarly, thin-film-based technologies operating under high strain levels will fail due to zero shifting. Moreover, as the pressure range increases, the proof pressure drops off rapidly due to the strain level approaching the yield point of the diaphragm material. Figure 3 shows typical strain values for pressure-sensing technologies. Krystal Bond technology offers a one-piece design and low operating strain, which are ideal for demanding hydraulic applications where pressure spikes and cavitation are of main concern.

Key Components For High Pressure

Pressure ports and the mechanical interface are crucial parts of the pressure transducer when it comes to safe operation for hydraulic systems pressurized to 45,000 psi (3,000 bar). Pressure ranges up to 7,500 psi can use ¼-in. tapered ports such as National Pipe Thread (NPT) or British Standard Pipe Taper (BSPT). Beyond this pressure range, a metal-to-metal seal must be employed in high cyclic or dynamic operation, Figure 4.

Straight threads such as ¼-in. British Standard Pipe Parallel (BSPP), G¼, ⁷⁄/₁₆-20 UNF, and ⁹⁄/₁₆-218 UNF use an O-ring to seal against the fluid. These O-rings are good for static operations up to 1,000 bar. However, under dynamic and high-vibration conditions, they must be derated to 400 bar as suggested by SAE. Otherwise, the fitting will loosen, and fluid will leak.

Greg Montrose is marketing manager and Karmjit Sidhu is vice president at American Sensor Technologies, Mount Olive, N. J. For more information, visit www.astsensors.com.

Compared to other components in a fluid-power system, the low cost of seals doesn’t earn them much respect. However, rod seals perform one of the toughest jobs in a fluid-power system. They must squeeze the piston rod tight enough to prevent pressurized fluid from leaking out of the cylinder. But if they squeeze too hard, they’ll wear prematurely and maybe even damage the piston rod surface. Not only that, seals must prevent leakage at high pressure, low pressure, varying temperatures, a wide range of rod speeds, and when systems sit idle for days on end.

Effective seals need to perform three basic functions:

Seal — sealing elements must conform closely enough to the microscopic irregularities of the mating surfaces (rod-to-seal groove or piston groove-to-cylinder bore, for example) to prevent pressure fluid penetration or passage (Figure 1);

Adjust to clearance-gap changes — the seal must have sufficient resilience to adjust to changes in the distance between mating surfaces during a cylinder stroke. This clearance gap changes size because of variations in the roundness and diameter of the cylinder parts. The clearance gap also may change size in response to side loads. As the size of the gap changes, the seal must match the size change to maintain compressive sealing force against adjacent mating surfaces; and

Resist extrusion — the seal must resist shear forces that result from the pressure differential between the pressurized and unpressurized sides of the seal. These shear forces attempt to push the elastomeric seal into the clearance gap between adjacent metal surfaces (Figure 2). The seal must have sufficient strength and stiffness to resist becoming deformed into the gap and damaged or destroyed.

Higher pressure improves sealing

High-pressure sealing generally refers to confining fluids at pressures above 5,000 psi. Below these pressures, standard energized urethane lip seals and U-cup seals function well without special provisions. Above them, some sort of special sealing devices are necessary.

Elastomeric materials also must seal while accommodating dimensional variations caused by manufacturing tolerances, side loads, and cylinder deformations under pressure. Understand that in general, sealing improves as fluid pressures increase. System pressure on the seal surface attempts to compress the seal axially. This compression forces the seal more tightly into the gland and helps improve conformability of the seal with its contacting metal surfaces.

If the clearance gap increases during the stroke, resilience of the compressed elastomeric seal causes it to expand radially and maintain sealing force against the metal surfaces. System pressure combines with seal resilience to increase compressive sealing forces when the clearance gap increases. It generally is true that, as system pressure increases, sealing force and the resulting sealing effectiveness also increase if the seal is correctly designed.

The seal’s internal shear stresses increase as system pressure increases. With increasing pressure, the stresses eventually exceed the physical limits of the seal elastomer, and it extrudes into the gap. Difficulties presented by high pressure are not primarily sealing problems, but are problems of keeping the seal in its gland while maintaining its structural integrity as increasing system pressures force the seal into the gap.

Almost all of the design and in-service technology of high-pressure sealing deals with protecting the elastomeric seal from the potentially destructive distortion caused by high system pressures. With proper backup to reduce the size of the gap, relatively fragile elastomers can successfully seal extremely high pressures.

When handling a 90-durometer energized urethane lip seal or U-cup at room temperature, the seal seems to be made of an extraordinarily stiff, tenacious material. It requires well-designed experiments and/or sophisticated computer simulations to visualize the state of such a seal inside a hydraulic cylinder at normal operating temperatures and pressures. At pressures as low as 600 psi for 70-durometer nitrile rubber and 1,500 psi for 90-durometer urethane, the seal cross section is significantly deformed. It changes shape almost instantaneously in response to pressure spikes or changes in the size of the clearance gap.

Material is the key

The key to high-pressure sealing is the use of a material or a combination of materials that has sufficient tear strength, hardness, and modulus to prevent extrusion through the gap. At pressures of 5,000 to 7,000 psi, the strongest elastomeric materials in standard seal configurations resist the extrusion without reinforcement. At higher pressures, the elastomeric sealing element must be backed by a higher modulus and harder material. Various more-or-less standard backup configurations have demonstrated their effectiveness over many years.

At pressures in excess of 20,000 psi, the extrusion gap must be closed and the elastomeric seal must be protected by a sequence of progressively harder, higher-modulus materials. Properly designed, this progression of materials prevents extrusion, tearing, cutting, or other destructive deformation of the elastomeric seal and distributes loads more uniformly to the element that bridges the gap.

Recent developments

In Europe and the United States, as the move to more environmentally friendly fluids grows, many types of vegetable-based and synthetic oils have been developed. Each has its own set of characteristics — many of which can affect sealing effectiveness seal material compatibility.

The seal industry has kept up with the technology by introducing new materials and blends to accommodate chemical and physical properties of these new fluids while still providing the sealing integrity users expect.

Material for this article was excerpted from the Fluid Power Handbook & Directory, which can be accessed from our home page by clicking on the Fluid Power Basics button.

The LCD display of the DG25 digital pressure gauge provides five full digits in ranges up to 25,000 psi. Features include accuracies of 0.5 and 0.25% FS, minimum battery life of 2,000 hr, an IP67 enclosure, selectable units of measure, and a 20-segment bar-graph indicator. A backlight and rubber protective boot are also available.

Ashcroft Inc., (203) 385-0408, www.ashcroft.com

Reclassifying mufflers can be installed directly into the exhaust port of cylinders, valves, and other air-powered equipment to reduce work-area noise and harmful oil mist. They are easy to retrofit to new and existing installations. Mufflers reduce noise up to 35 dBA to help meet EU noise directive (86/188/EEC) and OSHA standard 29 CFR-1910.95. Wrap design of the removable element eliminates oil-mist contamination of workers’ breathing air, keeping exposure well below the 4.32 ppm required by OSHA. Harmful open dead-end pressure is also eliminated. They have high airflow capacity to minimize backpressure. A reservoir for oil to accumulate at the bottom can be drained by attaching a 14-in. tube. They are available in sizes from ¹/₈ to 1-in. NPT.

Exair Corp., (800) 903-9247, www.exair.com

PQ-FV in-line flow controls use a tube-to-tube connection that can be installed as a meter-in or meter-out device. The PQ-C elbow controls are for lightweight applications when mounting directly to an NPT port on a cylinder or valve is required.

Intake air in meter-out versions flows freely through the flow control; exhaust air is metered out through an adjustment screw. With the meter-in style, air is metered in through an adjustment screw; exhaust air flows freely. Control is varied through a finely threaded adjustment screw.  A locking nut is provided so it can be secured in its final setting.

The controls are available in 25 different models: #10-32, ¹/₈, ¹/₄, and ³/₈-in. NPT.

Clippard Instrument Laboratory Inc., (877) 245-6247, http://www.clippard.com/link/hp1293889

The comprehensive 2013 Ladd Connector Selector covers TE Connectivity’s Deutsch industrial environmentally sealed electrical connectors. The guide is arranged by connector cavity count and includes product overviews, connector descriptions, contacts, tooling, and accessories.

LADD Distribution LLC, (800) 223-1236, www.laddinc.com

Series GRH parallel pneumatic grippers provide long jaw travel while accommodating long tooling lengths. Available in four sizes, the grippers have an extended support guide system with wide slot jaws to minimize tooling deflection, support large moment capacities, and provide side-load stability. A dual bore provides higher total grip force, and low breakaway pressure allows for gripping of a wide variety of part sizes, including delicate parts. Jaw travels up to 125 mm (4.921 in.) for gripping larger and multiple-sized parts.

PHD Inc., (800) 624-8511, www.phdinc.com/grh

An original-equipment manufacturer of custom automation equipment for the food-processing industry built a large pallet-transfer system to shuttle bins of poultry from a defeathering line to a final processing line. The poultry was placed into bins, 10 at a time, and the bins were stacked 10 high. The 10-high pallet-transfer system consisted of a floor-mounted rack-and-pinion drive system with a gerotor motor driving the pinion to move the pallets. The pallets were then shuttled to one of three locations to be off-loaded for final processing.

An optical encoder provided position feedback to the machine’s motion controller. The motion controller commanded an electrohydraulic proportional valve to drive the hydraulic motor’s motion accurately — to within ±½ in., in front of the correct off-loading point.

The OEM overcame the normal struggle of meeting the cycle time to provide smooth acceleration, deceleration, and positioning of the pallets. The system was tested on the OEM’s shop floor, then installed and commissioned at the poultry plant. Several months of smooth poultry operation ensued.

As usual, a call came in for increased cycle time and higher throughput. The bins were modified to accept 15 poultry bodies, and the original pressures on the system were raised to accommodate the 50% increase in load. The system pressure was raised to 1,800 psi and the cross-port reliefs to 2,200 psi. After a couple weeks, the shaft seal on the motor developed a leak. The motor, rated for 2,500 psi, was replaced. However, the new motor also developed a shaft seal leak in short order.

The motors were disassembled, but technicians found no indication of any internal damage. In fact, the motor manufacturer said they looked brand new and that internal components met
factory-new tolerances. With the rack-and-pinion design, side loading seemed to be the only possible cause for the leakage, so an overhung load adapter was installed to eliminate any side load being transmitted to the hydraulic motor’s shaft. This did nothing except allow the leakage to collect between the adapter and motor.

What do think was the problem?

Individuals who work on mobile equipment often require hydraulic and electrical knowledge for maintaining equipment in fixed factory settings. Industries such as energy, mining, construction, rail, waste management, agriculture, and oil and gas are loaded with mobile equipment. If you are faced with finding professional training for your fleet or unique mobile equipment, CFC Industrial Training may be able to help. CFC Industrial Training is one of the most-respected names for mobile and industrial equipment training, with a history of developing training programs that teach individuals how to maintain today’s technically advanced mobile equipment. CFC Industrial Training has standard classes developed for the mobile equipment industry that include:

• Level 1 Mobile Hydraulics – In-Depth Fundamentals

• Level 2 Mobile Hydraulics – Advanced Maintenance

• Level 3 Mobile Hydraulics – Design and Sizing

• Troubleshooting Mobile Systems using Schematics

• Hydrostatic Closed-Loop Systems

• Level 1 Mobile Electrical – Fundamentals

• Level 2 Mobile Electrical – Multiplex Systems

CFC Industrial Training is one of the primary training firms that provide Fluid Power Society Mobile Hydraulic Certification. Use discount code h&p6489 (which is case-sensitive) when you register for any training module, and you will receive a 6% discount. For more information, call (513) 874-3225, e-mail Tim Sheaf at tsheaf@cfc-solar.com, or visit www.cfcindustrialtraining.com.