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Position Sensor Technology Comparison for Hydraulic Cylinder Feedback 
Edward E. Herceg
Chief Technology Officer
Alliance Sensors Group a div. of H.G. Schaevitz LLC

Position feedback sensors for hydraulic or pneumatic cylinders have used one of three traditional technologies: Magnetostrictive, Variable Resistance, and Variable Inductance sensors. While other sensor technologies have occasionally been used successfully in this application, the focus of this article is the comparison among these three most popularly used technologies. As the demand for increased control and functionality has increased over the years, sensor- instrumented cylinders are becoming more important in the heavy industry, subsea, and mobile equipment worlds. Ultimately, a user or systems integrator must determine the requirements of the application and which technology best satisfies it on a total installed cost versus performance basis. The strengths and weaknesses of magnetostrictive, variable resistance, and variable inductance sensors are discussed below, along with a chart for feature-by-feature comparisons.

Initially, a point to be noted is that all of these common sensing technologies utilize a long probe that extends into a deep, small diameter blind hole which has been gun-drilled into the internal end of the cylinder rod. 

Magnetostrictive technology has been the preferred technology for high accuracy applications. The sensor, often called an LDT or MLDT, incorporates a stainless steel tubular probe and a short toroidal permanent magnet assembly around it that is installed in a counterbore in the piston. The most common package is designed to thread the sensors' electronics housing into an o-ring port in the back of a cylinder, with the long slender probe inserted into the rod's bore. It uses the “time of flight" principle to determine the magnet's position with high accuracy and moderate response time. The magnet is used to reflect a torsional mechanical pulse which is transmitted along a special wire inside of the probe called a waveguide. Typically, each of the magnetostrictive sensor manufacturers has its own style of magnet with unique mounting features like the number of holes, the hole pattern, etc. Magnetostrictive sensors can consume a fair amount of power and are not the most mechanically rugged sensors. They offer electrical performance over mechanical robustness, because they are subject to shock and vibration issues. Yet, while there are some potential drawbacks mechanically, the magnetostrictive sensor's package design is tailor-made for port-mounted in-cylinder use.

Variable Resistance potentiometer-type sensors, commonly called pots, are selected where purchase cost is a driver and high accuracy is not paramount. A resistance pot is usually embedded into the cylinder's rear end plate, as opposed to the port mounting of magnetostrictive sensors. It uses an insulated round carrier which is attached to the internal end of the gun-drilled cylinder rod and supports an electrically conductive wiper that contacts the surface of a partially conductive plastic probe. As the wiper moves along this plastic element, its resistance changes in a linear fashion, making it fairly easy to determine the carrier's position and, thus, the rod's position. Pots have been seen as a good position measurement solution for use in cylinders because of their ruggedness, favorable stroke-to-length ratio, and their large analog DC voltage output, which is a big percentage of the input voltage. The major drawback to resistance pots is wearout, especially if the cylinder is actuated at a high frequency, or even more importantly, dithered over a short range to improve a system's dynamic characteristics. Since a resistance pot is embedded into the cylinder, replacement of a worn out pot can be very time consuming and expensive, and could even result in the need for a completely new cylinder.

Variable inductance position sensors have been used in the cylinder industry but have not had the widespread recognition of magnetostrictive sensors or resistance potentiometers. This non-contacting technology has many significant advantages over resistance potentiometers regarding product life and long-term reliability, and usually can compete favorably with the performance of magnetostrictive sensors in terms of linearity, resolution, and frequency response, but at a significantly lower cost. Equally important is the fact that variable inductance sensors can withstand much greater shocks and vibration, such as those commonly found in heavy industrial and mobile equipment applications. 

Linear variable inductance sensors cover the middle ground between the higher level of performance and external port mounting flexibility associated with a magnetostrictive sensor and the ruggedness and price of an embedded resistance potentiometer. These sensors operate by measuring the resonant frequency of an oscillator circuit that uses an inductive probe whose inductance is varied by the position of the gun-drilled rod over it. Typically offered in full scale ranges of 4 inches (100 mm) to 36 inches (900 mm), both port-mounted and embedded packages are available, with connector and cable terminations that match those found on most catalog magnetostrictive sensors. These sensors offer either an analog DC voltage or current output, with an SSI digital output available for OEM applications. The variable inductance sensor presents a non-contacting solution that does not require a ring magnet. In fact, if a variable inductance sensor were installed to replace an existing magnetostrictive sensor, the magnet can be left in place in the cylinder rod end without interfering with the sensor’s basic operation. 

In the past few years, the requirements for instrumented cylinders for subsea applications have dramatically increased. Variable inductance sensors can be offered in a pressure-sealed version that allows a user to install the sensor/cylinder in a subsea environment in depths of 10,000 feet (3000 m) with 3000 psig of internal hydraulic pressure. 

Remote field calibration is a standard feature offered on many variable inductance sensors. This feature permits a user to scale the output of the sensor while it is being installed on the cylinder. With a simple push of a button to set the zero and the full scale output points, the sensor will give the desired full scale output over its newly set range, so it is no longer necessary to scale the unit in an operating control system.

In another fluid power application, though not commonly used inside of hydraulic cylinders, LVDTs are often used in spool position feedback applications for two-stage hydraulic valves. A short range variable inductance sensor with its simple inductive probe inserted into a hole in the end of the main spool is very often an easier installation than an LVDT that requires an isolation tube to seal off the its core from the valve’s pilot pressure.

Where there are still many fluid power applications where resistance potentiometers and magnetostrictive sensors are a good solution, these applications tend to fall to either side of a bell curve. Recent electronic advancements and the flexibility of package designs make variable inductance sensors very cost effective for mainstream in-cylinder applications that tend to be near the peak of that bell curve. 

Alliance Sensors Group
102 Commerce Dr
Unit 8
Moorestown, NJ 08057
Ph # 856-727-0250


IFPE & CONEXPO-CON/AGG 2014 attract nearly 130,000, set new exhibit & education records

The future on display as global industry showcase spotlights new product innovations, technology

IFPE and CONEXPO-CON/AGG 2014 took center stage in Las Vegas March 4-8 with tremendous energy and serious buyers. Total registration of 129,364 soared past the last edition of the shows as they achieved the second-highest attendance in their history. The shows also set new records for exhibit space, number of exhibitors and education tickets sold.

The co-located IFPE and CONEXPO-CON/AGG, at the Las Vegas (USA) Convention Center, delivered a global showcase of the newest product innovations and technologies for the construction, construction materials and fluid power/power transmission/motion control industries with more than 1,000 new products and services on display.

Attendees also took advantage of the shows’ strong industry education programs and the unparalleled opportunity to connect with industry peers, take the pulse of what’s happening and learn what the future holds.

“The enthusiasm and traffic on the show floor was just incredible. Exhibitors cited the high quality of attendees; they told us these were serious buyers and reported robust sales to existing as well as new customers that exceeded their expectations,” stated Megan Tanel, CONEXPO-CONAGG show director.

Quality Attendance, International Scope
IFPE & CONEXPO-CON/AGG 2014 maintained the growing international scope of the shows with international registrations totaling more than 31,000, or an increase of nine percent from the most recent events. The number of countries represented increased to 170 from 159 in 2011, and the number of international attendees matched the record 24 percent of total attendance set in 2011. International attendance drew heavily from Latin America, China, Canada, and Europe.

More than 75 percent of show visitors were in managerial roles (with 36 percent of these with the top titles of president/owner and vice president/general manager/chief financial officer).

Both shows set new records for exhibit space and number of exhibitors, CONEXPO-CON/AGG with more than 2.35 million net square feet of exhibit space and more than 2,000 exhibitors, and IFPE with more than 161,000 net square feet and 400 exhibitors.

A record 41,000 education ticket sales were sold to the shows’ education programs, underscoring their relevance to helping attendees succeed in today’s business environment.

“CONEXPO-CON/AGG and IFPE 2014 reflected the feeling of momentum building in the industry. We are industry-run shows with industry needs put first; these show numbers are a testament to the value attendees, exhibitors, and other stakeholders derive from their participation,” stated Melissa Magestro, IFPE show director.

Global Industry Gathering Place
Among the show visitors were Acting U.S Deputy Secretary of Commerce Patrick D. Gallagher, Acting U.S. Deputy Secretary of Transportation Victor Mendez and former U.S. Rep. James Oberstar, who served as chairman of the House Transportation and Infrastructure Committee from 2007 to 2011.

The shows were chosen for the prestigious U.S. Department of Commerce (DOC) International Buyer Program, which helps facilitate global attendance. More than 50 official international attendee delegations were organized by DOC as well as show industry partners.

More than 95 allied associations and groups were official supporting organizations, coming from the U.S., Canada and 16 other countries worldwide.

Several national industry associations held their annual conventions or high-level board meetings at the shows; they joined hundreds of other industry and company meetings, from large events to smaller committees and other groups, all taking advantage of the shows to meet and share knowledge and learn from one another.

Education and Exhibits
The CONEXPO-CON/AGG 2014 education program covered 120 sessions over 10 targeted tracks. The IFPE Technical Conference anchored IFPE 2014 education, joined by half-day “college-level courses” and a new Fluid Power Seminar series, from Hydraulics & Pneumatics magazine.

CONEXPO-CON/AGG featured a new Demolition & Recycling exhibit pavilion from the Construction & Demolition Recycling Association (CDRA) and the Technology & Construction Solutions pavilion from the Associated General Contractors of America.

IFPE featured exhibit pavilions from the Power Transmission Distributors Association (PTDA) and for sensors manufacturers and product suppliers.

Reinforcing the global scope of the shows were eight international exhibit pavilions: CONEXPO-CON/AGG with China, Ireland, Korea, Spain and United Kingdom, and IFPE with China, Italy and Taiwan.

Show safety and education/training events at the shows included:

NRMCA International Truck Mixer Driver Championship, from the National Ready Mixed Concrete Association
Lift Safety Zone, from NCCCO National Commission for the Certification of Crane Operators and IPAF International Powered Access Federation
Crane Operator Rodeo from Maximum Capacity Media
Industry recognition and networking events and programs also amplified the show experience:

Innovation Awards program (from Diesel Progress magazine and global powertrain specialist ZF Friedrichshafen)
Young Leaders event (from Construction Equipment magazine)
Quality of Life industry recognition campaign (from Dexter + Chaney)
5K Run/Walk benefiting the non-profit Injured Marine Semper Fi Fund (from Maximum Capacity Media)
Night at the Race Track hospitality event at the Las Vegas Motor Speedway
Visit and for the latest show information.

To view Photos, visit online or in Media Services/Photos.

To hear what people onsite were saying about the show, visit online at -

and see these links:


Solutions Come Together

IFPE is the leading international exposition and technical conference dedicated to the integration of fluid power with other technologies for power transmission and motion control applications. Held every three years, the exposition showcases the newest innovations and expertise.

IFPE 2014 Will Feature
-Over 400 exhibitors – making this the largest IFPE!
-Product concentration areas; making it easy for visitors to locate specific products, services and exhibitors of interest
-More than 100 cutting-edge education sessions at the IFPE Technical conference, focusing on the newest technologies, best practices, the latest research and developments, including:
-Keynote presentations
-College-level courses in hydraulics and pneumatics
-Thousands of industry professionals from all sectors of the fluid power, power transmission and motion control industries.
Agricultural Engineering
Amusement Machinery
Automotive Mfg./Supplier
Chemical & Petroleum Processing
Electrical Machinery
Engineering Services
Factory Automation
Fluid Power Products
Instruments, Controls
Machine Tools
Material Handling
Metal Processing
Off-Highway Vehicles
On-Highway Vehicles (not autos)
Plastics/Rubber Working Machinery
Power Transmission

Co-located with CONEXPO-CON/AGG 2014, the largest international gathering place for the construction industries


HAWE Valves Assists Off-Road Motorsport Vehicles

CHARLOTTE, N.C.– January, 2014 – HAWE Hydraulics, a leading global manufacturer and supplier of sophisticated hydraulic components and controls for the mobile, industrial, and renewable energy markets

Dakar 2014, is a legendary sporting event that challenges drivers‘ endurance, racing skills and strategic navigational competencies. This intense off-road race is made up of two marathon stages that stretch across miles of South America’s desertous terrain. Drivers take great precautions ensuring their vehicles can withstand the wear and tear of the sand dunes and off-road courses. For this reason HAWE Hydraulics took part in servicing the dual hydraulically mounted jacks for the Chevy Colorado Z71 Rally Raid prototype vehicles.


HAWE’s reputation for long-lasting, durable products make them a perfcect match for this project. SG 1L – AKS valves were used for the racing vehicles. HAWE’s SG Directional Spool Valves allow up to 400 bar, 100 lpm and serves to control the oil flow and directional movements of the jacks. Since the valve system is entirely made up of steel the housing unit is resistant to pressure surges and leakages. This eliminates the chance of hairline cracks or other damages caused by the harsh desert conditions.

About HAWE Hydraulics North America:
Sixteen years ago North America was introduced to HAWE Hydraulik through its American subsidiary HAWE Hydraulics. Today, the partnership brings more than 60 years of German engineering and experience to North American mobile and industrial markets. HAWE provides integrated services that include design, manufacture, set-up, a distributor network, and local inventory. Based in Charlotte, NC, HAWE Hydraulics is positioned to respond quickly to service needs, as well as provide prototypes in a timely manner. Headquartered in Munich Germany, HAWE Hydraulik is an ISO 9001:2000 certified international supplier with a strong focus on supporting rapidly developing niche markets.


Altair ProductDesign Unveils the World’s First Series Hydraulic Hybrid Transit Bus

BUSolutions LCO-140H to revitalize urban transit by increasing fuel economy by 110 percent and reducing 12-year fleet operations cost by $50 million for the average sized transit authority

TROY, Mich. – Sept. 7, 2011 – Altair ProductDesign, a global product development consultancy and wholly-owned subsidiary of Altair Engineering, Inc., today unveiled the world’s first series hydraulic hybrid transit bus. The LCO-140H (Low-Cost of
Ownership-1st 40-foot Hybrid) was developed under the BUSolutions program in partnership with Automation Alley, in an effort to revitalize public bus transportation in America.

Compared to the database of buses tested at Altoona, where the Federal Transit Administration (FTA) certification program is conducted, the LCO-140H fuel economy results are 110 percent better than conventional diesel buses and 30 percent better than the leading diesel-electric hybrid buses available today. The LCO-140 achieved an industry high fuel economy of 6.9 mpg when tested using the downtown “stop-and-go” duty cycles and test protocol established by the FTA for transit bus certification testing.

BUSolutions is projected to lower the cost of ownership by $170,000 per bus as compared to a conventional diesel bus. With the average local transit authority operating approximately 300 buses, the savings could reduce a city’s cost of transit bus operation by approximately $50 million. When compared to an estimated $27 million increase in operational costs for a similar electric hybrid fleet, it is clear the LCO-140H could revolutionize the transit industry by providing reduced fuel consumption and emissions while improving the fiscal performance of a regional transit authority.

BUSolutions has been a collaborative effort between public and private entities to research, develop and commercialize advanced transit bus systems that are significantly more fuel efficient, have lower operating and maintenance costs, are competitively priced and can operate without updating the infrastructure of existing transit authorities.

In addition to investments by Altair and Automation Alley, BUSolutions has been funded by multiple federal and state programs including the FTA and the Michigan Economic Development Corporation (MEDC). It also has received exceptional local support by southeast Michigan congressional members, transportation industry partners, and local transit authorities SMART and the Detroit Department of Transportation (DDOT).

“This project has been a collaborative effort from start to finish throughout the development, design and test phases. We would not have exceeded the goals we had set for ourselves had we not applied our knowledge and unique technologies to produce this revolutionary bus,” said Mike Heskitt, chief operating officer at Altair ProductDesign. “BUSolutions demonstrates Altair’s
expertise and capabilities as a concept-to-release, full vehicle development partner.”

“We are thrilled to have partnered in the BUSolutions program that is putting Michigan at the forefront of solving emerging public transit technology issues through innovation and collaboration,” said Ken Rogers, executive director at Automation Alley. “Goals were set when this program started to produce a transit bus that was more fuel efficient, more affordable and more cost effective to operate for city transit authorities, and this project has both met and exceeded those goals.”

Additionally, BUSolutions strategically partnered with regional and global high-tech manufacturers that assisted in incorporating state-of-the-art components and technologies from the transportation sector. Program sponsors include Parker and Meritor, which contributed significant driveline systems and knowledge. Various levels of support have been provided by PRAN, Sika Corporation, Meritor Wabco, Alcoa Wheel Products, Carrier Corporation, LADD Industries,Haldex, Shaw Development, Tenneco, USSC Group, Cummins Bridgeway, Multicolor Specialties and Williams Controls.

Altair has worked closely with local transit authorities, SMART and DDOT, to ensure the newly designed bus platform will meet regulatory requirements and address the needs of bus drivers and riders. Altair also established the BUSolutions Advisory Board to offer insight into broader community needs, as well as perspective on actual ridership issues and public-interface
ergonomics. As a result, Altair ProductDesign successfully engineered the bus to incorporate design principles that will enhance the rider experience.

The LCO-140H Bus will also be demonstrated at the American Public Transportation Association (APTA) Expo in New Orleans Oct. 3-5 at booth #2281. For more information, visit the Altair events website.

About BUSolutions
Launched in 2005, the Altair BUSolutions program was established to develop and commercialize an advanced bus platform that lowers the total cost of ownership and environmental impact of commercial buses without updating the infrastructure of existing transit authorities. Leveraging the company’s deep domain knowledge in vehicle systems and cutting-edge, simulation-driven
design practices to develop the design, Altair successfully partnered with Automation Alley, Michigan’s largest technology business association, to secure federal funding to build working technology demonstrators for future commercialization. For more information, visit

About Altair ProductDesign
Altair ProductDesign is a global, multi-disciplinary product development consultancy of more than 500 designers, engineers, scientists, and creative thinkers. As a wholly owned subsidiary of Altair Engineering, Inc. (, this organization is best known for its leadership in combining its engineering expertise with computer aided engineering (CAE) technology to deliver innovation and automate processes. Altair ProductDesign firmly advocates a user-centered, team-based design approach, and utilizes proprietary simulation and optimization technologies (i.e., Altair HyperWorks) to help clients bring innovative, profitable products to market faster. To learn more, please visit


Twin Cities Manufacturer Part of the Solution to Stop Gulf Oil Leak

Modified valve from Continental Hydraulics Helps Waterjet System Unclog Containment Dome

(Minneapolis, Minn.) – There’s no question the BP oil leak crisis takes engineering, thought and industry best practices. Intervention is rough according to James Miletich of Oceaneering’s ROV Division. “You’re always fighting something. It’s never easy,” he said.

Recently, hydrate ice crystals formed inside BP’s 40-foot-tall containment system aimed to capture leaking oil—and ultimately clogged the system. Hydrate gases crystallize like ice in cold waters and high pressure deep beneath the ocean’s surface.

Minnesota company Continental Hydraulics, in partnership with Jet Edge, Inc. and Chukar Waterjet, Inc. developed a solution to help fight the problem. The company’s DO8 valve was used to operate Jet Edge’s waterjet pump enabling the jet stream to blast away the hydrate crystals.

“The timeliness and schedule was intense—but we were pleased to deliver a modification to our product capable of withstanding the harsh undersea environment and enormous water pressure at a depth in excess of 5,000 feet,” said Continental Hydraulics general manager Jeff Brandt.

Jet Edge’s custom engineered waterjet intensifier pump was dropped into the sea to power a robot-operated waterjetting lance— eliminating the hydrates. This equipment is the first-known waterjet system capable of operating in water depths in excess of 5,000 feet, opening a new frontier for waterjet technology.

Chukar Waterjet, Inc. general manager Bruce Kivisto said, “We worried about 2300 pounds of force and the harsh exposure to that valve. Continental Hydraulics recognized the importance, the challenge and delivered a critical component to our success.”

Kivisto provided onsite application and engineering services throughout the project, recently returning from several weeks aboard a boat just 50 yards away from the Discoverer Enterprise. He says the solution appears to be working and will continually be monitored.

Continental Hydraulics of Savage, Minn. is a manufacturer of high performance hydraulic pumps, valves and power units. Their products are used in some of the most severe conditions and their reputation for superior durability and performance continues to grow. The engineering staff at Continental is continually at work to improve current products and develop new fluid power technologies. In addition, Continental Hydraulics specializes in response time and delivery for challenging custom orders. For more information, visit

Do Minor Oil Leaks Really Matter?

By Jack Weeks

We are often asked if minor leaks are really much of a concern. Repairing them takes valuable time that most maintenance shops feel should be devoted to issues that could halt production. Everyone knows that a ruptured hose needs to be addressed right away. But the mistaken belief that a minor leak doesn't cause a problem is certainly not uncommon. It is even a little surprising how many people seem to believe that hydraulic machines are "supposed to leak a little". We have heard everything from "The oil that bypasses the cylinder seals helps to keep the rods lubricated" to "The leaks in our system help keep our oil fresh since we have to replace so much of it all the time". These same people however would be dissatisfied if their automobile's power steering pump, automatic transmission or brake lines "leaked a little bit".

So how much does a minor leak cost? To answer that question, we have to first explore all of the costs involved. Most people think that the only cost is the amount of oil that has to be unnecessarily replaced. But this is not the only cost associated with hydraulic leaks. The actual costs include:

Replacement Oil
Environmental Concerns
Cleanup Costs
Loss of Machine Efficiency

Replacement Oil

This is the most obvious cost. A drop of hydraulic oil doesn't cost very much even at today's prices. But if your machine loses a drop of oil every second, it adds up. A drop every second will equal about one gallon per day. 30 gallons per month and 365 gallons per year. Depending on your geographic area, the type of oil you use in your machine and the volume you purchase you pay between $6 and $10 per gallon. This means that a leak that loses one drop per second (most machines lose many times that) is costing you between $2190.00 and $3650.00 each year in replacement oil alone.


The cost of replacement oil is bad enough but oil leaks pose a safety hazard in almost every facility we have visited. The cost of safety hazards is hard to calculate. But even one incident can cost a few hundred dollars or a few million.

Environmental Concerns

Not everyone agrees with the Environmental Protection Agency's standards and policies. But we doubt anyone believes that EPA requirements will become more lenient in the near future. If any changes are made in EPA standards, they are likely to include stricter controls and heavier fines and penalties. Currently an uncontained spill of more than one gallon can require EPA notification. Fines in the millions of dollars are not uncommon.

Cleanup Costs

Often the costs of routine cleanup are ignored, but that doesn't make them go away. Time devoted to cleaning up from a leak is time that could be spent on more productive endeavors and could result in overtime costs that would otherwise not have to be incurred. And we cannot ignore the cost of cleanup equipment, absorbent pads and detergents. Annual cleanup costs can easily add $2000 or more to our drop-per-second leak.


Those of us who can remember a time when waste oil companies paid for the privilege of coming to empty our waste hydraulic oil tanks can probably also remember getting change back from a five dollar bill after having someone else fill up our gas tanks, check our oil, check our tire pressure and clean our windshield. These days an environmentally acceptable means of disposing of waste oil can cost $3 per gallon or more. There's another $1100 annual cost to our minor leak.


It's easy to forget that if oil has a way out of the machine, contaminants have a way in. Airborne contaminants, particles and water all can wreak havoc with a hydraulic machine. Over 96% of all hydraulic failures can be directly traced to contaminants in the oil. Not all of those contaminants come from an oil leak of course, but any that we can stop will pay big dividends in parts that do not have to be changed unnecessarily, reduced down time and greater intervals between flushing or changing the oil.

Loss of Machine Efficiency

A machine that leaks is working harder than it has to. This means that, while the machine appears to be functioning as it should, our energy costs have increased. Suppose our one-drop-per-second leak causes the power bill to increase by five cents per day. That's another $18.25 in annual cost. Not a huge amount, but it could probably buy us dinner somewhere. And it adds up if it occurs in several machines.

So assuming that no one gets hurt from slipping on oil and the EPA doesn't have to visit, each drop-per-second leak is costing somewhere between $5000 and $7000 every year. And hydraulic leaks, unlike paper cuts, do not heal. They gradually get worse. At some point, what starts as a "minor" leak can become a machine outage. No leak is so minor that it should be ignored.

GPM Hydraulic Consulting, Inc.
Box 1376
Monroe, GA 30655
(770) 267-3787

Funny Noises

By Jack Weeks

Not long ago on a consulting job, I noticed a loud hissing sound coming from a machine (not the machine I had been called to help diagnose). I asked the man I was working with about it and he said, "It's done that as long as I've been here. I guess it's supposed to sound like that - the machine works fine.". But it didn't sound normal to me. Looking a little more closely, I noticed a very large, relatively new heat exchanger installed on the machine. The man I was with explained that the machine used to overheat, so they installed a larger heat exchanger and that fixed the problem. Watching and listening through a full cycle of the machine, I noticed that the hissing sound was much louder at idle than while the machine was running. Placing my hand on the relief valve, I found that it was so hot I could not keep my hand on it. The problem was obvious - at some point, someone turned up the pressure on the pump compensator and it was now adjusted above the system reliefvalve setting. The pump was operating at full stroke all of the time. Any flow not being used by the machine would dump across the relief valve. I suggested that he reduce the setting on the pump. I could tell that he didn't really want to, because he was afraid the machine would stall. So I told him to wait until the machine was idle again, then turn it down just a quarter turn. Once the machine was in an idle condition, he made the quarter turn counterclockwise on the compensator and, with a puzzled look on his face, noticed that the pressure reading on the gauge did not change. He made another
quarter turn. Still no change. Then another and another. "I don't think this valve is working - turning it has no effect on the pressure.". But I could still hear the relief valve dumping so I explained to him that the system pressure was currently being determined by the relief valve, not the pump compensator. After approximately one and one-half full turns of the compensator adjustment, the hissing sound stopped. The gauge pressure began to drop. I had him stop when the pressure on the gauge was about 250 PSI below where it had started. The machine was noticeably more quiet. "When it starts back, I don't think it will work without stalling now that we have the pressure this low.". I said,
"Let's see.". When the machine began to cycle again, not only was it quieter than it had been, but the actuators were moving faster than they had before. I also told him that the current draw from the electric drive motor would likely be considerably less than before, too. The original heat problem had never really been addressed, only one of the symptoms had been masked.

This is by no means an isolated incident. Hydraulic machines simply do not make unusual sounds unless something is wrong. Just because the machine still appears to be functioning normally does not mean that it needs no attention. And a strange sound coming from the machine is often one of the very first signs of impending trouble. It has always been amusing to me how the same person who would take his car immediately to a mechanic if he heard a strange sound will ignore unusual noises in a multimillion-dollar hydraulic machine. Of course, there is no such thing as a silent machine. All industrial machines make noise. But sound is a form of energy and any unusual sound is, at the very least, a waste of some of the energy applied to the machine. There are hundreds of abnormal sounds a machine may make and an exhaustive list of every possible one could probably
fill a book. All of them can mean trouble, but in a hydraulic machine, a few of them are harbingers of serious issues that can cost a lot of money in very little time.

Relief Valves and Other Pressure Controls

Relief valves, for the most part, are designed to open only when something is wrong. Typically they are installed to keep system pressure from reaching dangerous levels With only a few exceptions, hydraulic machines are not designed to dump across their relief valves continuously. The hissing sound described above and a significant temperature gain across the relief valve are the most obvious indications that a relief valve is dumping. Heat is also a form of energy, so when a relief valve dumps a corresponding increase in current draw will usually be indicated on the electric drive motor. The excessive heat will not only waste energy but will also degrade the hydraulic oil. Most relief valves are set well above normal operating pressure, so when they are dumping the system pressure is usually higher than normal. This causes excessive wear all over the machine. If left
unchecked, shock spikes attack hoses, fittings, pipe clamps and seals. Mechanical wear to bushings, bearings, supports and connectors is also accelerated. Other pressure controls, such as reducing valves and counterbalance valves are often intended to be open regularly. But this doesn't mean they should always make excessive noise. A whistling sound or erratic hissing often suggests that they are improperly adjusted or stuck open. A good rule of thumb is if it doesn't sound right, it probably isn't. Slamming of actuators, stalls and excessive heat generation are the early symptoms of problems with these valves.

Pump Cavitation

A pump that is cavitating makes a steady, high-pitched whining sound. Since the sound is steady and does not reflect changes in the movement of the machine, it is often confused with bearing wear in the pump. Often a pump is replaced unnecessarily because it is cavitating. Cavitation is caused when the pump is trying to deliver more oil than it can draw into its suction line. This may be because the oil is too cold and the viscosity is high or because the drive motor has been mismatched and is turning the pump too fast, but most of the time cavitation is caused by some blockage in the pump suction. Usually this is the result of a plugged suction strainer or filter. Naturally, when a pump is
replaced, its suction filter element is changed or its suction strainer is cleaned while everything is apart. The cavitation stops when the new pump is installed, but actually it was the cleaning of the strainer or the replacement of the suction filter element that stopped the cavitation.

In addition to the steady high pitched whining sound, another symptom of cavitation is a reduced flow from the pump, which will result in a reduced speed of the machine. Obviously, a pump can deliver no more oil than it can get into its suction line. The pump will destroy itself if the cavitation is not addressed.

Pump Aeration

Often confused with cavitation because of its similar sound, aeration occurs when outside air enters the suction side of the pump. The pressure in the pump suction line is below that of the surrounding atmospheric pressure, so a leak will result in air coming in, not hydraulic fluid coming out. It can be distinguished from cavitation by its somewhat more erratic whining sound. The sound of cavitation is from the implosion of air molecules suspended in the oil. Since the molecules are distributed very evenly throughout the oil, the sound of cavitation is very steady. But the amount of air that leaks into the suction side of a pump is heavily dependent upon the flow of hydraulic oil. The sound will
therefore change as changes occur in the machine. It will also likely be accompanied by a sound similar to gravel or marbles rattling around inside the pump. If you can view the oil in the reservoir (most reservoirs have screens and baffles that get in the way of seeing the oil) you may also note some foaming of the oil. If a pump is allowed to aerate it will wear rapidly. But beyond damage to the pump, the rest of the hydraulic components will also be at risk. Aerated oil causes a number of
problems. When air is in the line, the machine will perform sluggishly (think about the last time you had air in the brake lines of your car). Air viscosity is well below that of oil. The reduction in viscosity will result in leaks, faiure to lubricate and heat problems. Air also becomes somewhat unstable at the high pressures hydraulic machines are operated, so corrosion and seal damage are likely. Air that enters the suction line probably also brings with it a host of contaminants to damage components.
If a leak in the suction line is suspected, squirt oil along the line. If aeration ceases briefly, you have found your leak. A worn shaft seal on a fixed displacement pump can cause it to aerate. Spray some shaving cream around the shaft seal and see if holes are drawn into the foam. Sometimes there is no float switch to shut the machine down when the oil level is too low. If the level of the oil gets too close to the suction strainer, a vortex will develop drawing air into the suction line along with the oil. Aeration can also be caused by the wrong shaft rotation or by improperly aligned couplings.

Directional Valve Noise

For the most part, directional valves should operate quietly - no more than a faint "click" on very quiet machines. The small amount of noise a directional valve makes is almost always completely drowned out by the rest of the machine. If you can hear a directional valve spool shift, chances are very good that there is a problem. If the pilot chokes are improperly adjusted on a two-stage directional valve, it will audibly slam when it shifts. The spool can easily be damaged, but the greater issue is the shock it introduces to the machine. Sudden movement of the valve spool causes shock throughout the machine and the weaker points of the system will suffer. Adjust the pilot chokes for smooth shifting of the spool and greater component longevity.

Cylinder Noise

Cylinders should move with almost no noise. If a cylinder makes noise, it may be binding or slipping. A bent rod will wear seals and mechanical linkages rapidly. Slippage degrades the performance of the machine and sends contaminants from the resulting worn seals out to other components. A noisy cylinder should be rebuilt or replaced as soon as possible.

Hydraulic Motor Noise

Hydraulic motors can make many of the same noises as hydraulic pumps. Just as pumps can aerate and cavitate, so can motors. And the same results will develop. A motor that is cavitating will destroy itself rapidly. This usually occurs on motor drives that have loads that can be overcome by gravity, causing the load to "run away". A meter out flow control or brake valve can correct this.

Listening to a machine and paying attention to the sounds it makes can pay off in large dividends by catching problems early before they become outages.

Jack Weeks entered GPM’s organization in January of 1997 as a CAD draftsman and hydraulic instructor. He has trained thousands of electricians and mechanics in Hydraulic Troubleshooting methods. His computerized animations have made GPM's presentations and training CD's the recognized leader in the industry. He received his education from the Georgia Institute of Technology School of Electrical Engineering and the Department of State Foreign Service Institute. Jack is an experienced draftsman and taught telecommunications equipment operation and repair for the Central Intelligence Agency at American embassies overseas.

GPM Hydraulic Consulting, Inc.
Box 1376
Monroe, GA 30655
(770) 267-3787

The "Hole" Story Behind Cartridge Valve Performance

Latest precision bore machining technology drives performance and quality improvements

Rich Moellenberg
Manager, Global Technology Support
Sunnen Products Company

A new generation of honing technology is playing a vital role today in improving product performance for fluid power components, providing manufacturers a unique ability to
size and finish valve bores precisely, with exceptionally high process capability (Cpk) levels. The new honing technology, known as precision bore machining, can control bore size
with quarter-micron accuracy (0.00001 inch), correct geometric errors in the bore, and produce a specific surface finish with lubrication and seal enhancing properties.

What's this mean in terms of performance in a cartridge valve? Conventional honing
straightens a valve bore and precisely sizes it. This allows reduced clearance between the
bore and mating parts, greatly reducing valve leakage. The tighter fit and correct geometry
help lower hysteresis and allow higher operating pressures with overall greater system
efficiency. Finally, honing creates surface finishes that wear at a slower rate to enhance
valve life. The crosshatch finish left by conventional honing improves the uniformity of
the lubricating film between sliding parts for more consistent performance, especially in
adverse operating conditions.

What is honing? Conventional honing is an abrasive machining process whereby a tool
with expanding stone assemblies rotates in the cylinder bore, while the tool or the part
reciprocates rapidly during the process. A conventional honing tool may contact the entire
length of the part's bore, giving this process a unique capability to correct geometric
error in the bore shape. Honing generates little heat and stress, so the surface integrity
of the bore is excellent and can be finished to a specified level of roughness.

It may seem a contradiction, but attaining performance enhancements with honing
actually lowers costs for the valve maker and can create opportunities to offer longer
product warranties. Here's how.

Any valve manufacturer can purchase basic screw machined components from high-
quality vendors, but tolerances for these parts are rarely "state of the art" precise. A
bore tolerance of 0.002 inch (0.05 mm) is considered acceptable by most machinists, while
honing produces bore tolerances of less than 0.00005 inch (<0.0013 mm).

In terms of the valve manufacturing process, various hole making operations, such as
boring, drilling and reaming are capable of producing excellent tolerances, but when a
manufacturer requires a high process capability – such as 1.33 Cpk – for quality purposes,
the acceptable tolerance level must shrink to meet this. For rule-of-thumb purposes, when
the target is 1.33 Cpk process capability, manufacturers find they have to hold about 75% of
the print tolerance; at 1.67 Cpk, it drops to about 60% of tolerance, and the average of the
measurements needs to be targeted very tightly on the mean of the tolerance. Holes produced
satisfactorily on a lathe for years that suddenly have to meet process capability of 1.33 or
1.67 Cpk may require a much narrower bell curve of distribution to stay between the upper
and lower support limits. "Flyers" at the fringes of the curve become unacceptable.

How does "process capability" translate to real world results? The classic Motorola
Six Sigma quality program (six sigma is a 2.0 Cpk process capability) projected a defect
rate of 3.4 per million.

High process capability requires a machining operation that's easy to "dial in" with
great precision, and very stable once the process is established. For example, a lathe may
get to just a certain value, but if tweaked a little, will jump to a value out of spec and
throws the process off. A computer-controlled hone can easily get within 10 millionths of a
specified size, and with the resolution on the feed systems of today's machines, the
variability is very small. Size control is not the only issue. Honing allows tailoring of
the surface finish and then leaves a crosshatch pattern on the bore of the cage.

Alternative processes, such as turning and single-pass honing, cannot produce
conventional honing's characteristic crosshatch pattern on the bore surface. Conventional
honing leaves a very desirable crosshatch pattern, which can be visualized as two opposing
helical patterns that remain on the bore surface. This is the same surfacing technology used
in automotive cylinder bores, particularly in performance racing. The crosshatch pattern
can be controlled to produce a specific angle and depth, which manufacturers use to control
the retention and distribution of lubricating oil films. A crosshatch surface ensures a
consistent full-length flow path for lubrication around the mating parts of the valve.

Conversely, bores finished with single-pass honing, or a single-point tool will have
a faint, single helical pattern on the surface. The resulting "threaded" finish can lead to
lubricating films being pushed out of the bore.

In addition to the crosshatch, honing also allows tailoring of the bore's surface
finish to a desired spec. It seems contradictory, but an ultra-smooth surface finish will
tend to diminish the lubrication between mating parts, actually increasing frictional
resistance. It is common for manufacturers to monitor the surface parameter Ra (average
roughness), but parameters such as Rk, Rvk and Rpk can also be monitored – and controlled
with honing – to influence the performance of mating parts.

Conventional honing improves the performance of valves by correcting geometric error in the part, too. A conventional honing mandrel – which contacts almost the full length of
the bore while the part reciprocates – can correct geometric error (straightness, cylindricity) from screw machining, or distortion from heat-treating or stress relief. In contrast, a single-pass honing tool is tapered, so only a part of the tool's length represents the final size. This part of the single-pass honing tool tends to follow existing path of the bore, so a curved bore will tend to remain unchanged. This is
especially true for parts with a length/diameter ratio exceeding 1:1.

The controlled fit, finish and clearance produced by honing result in a more
efficient hydraulic circuit. The precision size and surface finish help eliminate leakage.
Honing significantly reduces hysteresis and improves the low-voltage reliability of
electrically actuated valves, an advantage for units installed on mobile equipment.

What's on the horizon in honing technology? The latest generation of machines is
designed to function as fully automated cells with integrated air-gaging feedback for
closed-loop control of the process. It sorts parts by size after processing, and all the
parts fall within a size range of 0.000125".

Glossary of terms

Cylindricity – The tolerance zone limited by two coaxial cylinders a distance apart. A
typical spec would state: the toleranced cylindrical surface shall be contained between two
coaxial cylinders 0.0002" (0.005 mm) apart.
Rk – The core roughness, or actual working roughness of the surface that would be left after
the peaks have been eroded.
Rpk – The average peak height, which usually erodes quickly during initial part cycles.
Rvk – The average valley depth, usually used for retention of lubricating film.

Sunnen Products Company
7910 Manchester Ave.
St. Louis, MO 63143
Tel: 314.781.2100

Pressure Sensor Fundamentals Associated with Hydraulic Systems

Hydraulic systems use incompressible liquids with low activation pressure to control high pressure actions. From the brakes that stop our automobiles, to fork lifts that move and stack heavy boxes in warehouses, to the bulldozer moving dirt for the new highway, hydraulic applications are all around us. When the warehouse operator pulls the lift lever, he activates a hydraulic pump that delivers fluid under pressure to a piston to lift the load. The amount of fluid and pressure are a function of the load. A heavier load requires the pump to increase the pressure on the fluid to lift the load and the higher the load is lifted, the more fluid is required to push the piston up.

The ability of a hydraulic system to match the amount of work done by the pump to the size of the load is one of the defining characteristics of a hydraulic system. In most systems, under no load situations, no energy is expended by the hydraulic pump. A light load may require only 15% of the capacity of the pump while heavy loads can push the pump to the limit. In that way, the amount of energy used to run a hydraulic system is dependent on the load. The pump does not work full time at a fixed rate to lift a light load.

There are few practical alternatives to hydraulics. Mechanical systems could be designed with motors and gears but those systems would have to be sized for the maximum load and would be large and inefficient. Pneumatics or air pressurecould be used in some applications but air compresses and any leak would immediately deflate the system. The air compressor size and power requirements would be significantly larger and more complex than the hydraulic system. While hydraulic systems do spring leaks, it takes time to drain all the fluid out of a system through a leak and it can be detected and repaired before damage is done to the operator or system.

Pressure sensors play a key role in hydraulic systems. They can detect leaks in the system and insure that enough pressure is available on demand to perform the job required. They can provide a signal when the pressure exceeds system design parameters or if the load is too heavy for the system to safely handle.

Hydraulic systems are characterized by pressures of 6,000 PSI and above. Pressure spikes caused by the pumps and the applications can be significant and can easily double the pressure that the sensor is expecting to see causing sensor failure if not anticipated. Many times these pressure spikes are of very short duration and require specialized equipment to detect. The operating environment may see high vibration, severe shocks and extreme temperatures. Because of the
severe environment, the technology used to build rugged and reliable pressure sensors must be very robust. Pressure sensors such as Kavlico’s P4000, PT250, and P5000 used in hydraulic systems use welded, stainless steel construction. Pressure sensors that use elastomeric compounds for the
main media seal present an opportunity for the seal to become the weakest link and rupture, creating hydraulic fluid leaks. In addition, the seal material may be incompatible with additives
or impurities used to optimize the base fluids.

Piezo-Resistive based sensors such as the Kavlico P4000 and P250 (Figure 1) use welded oil filled headers with stainless steel isolation diaphragms to protect the sense technology.
(Figure 3) is a cross section of the pressure media interface for that type of product. The sense element is a high pressure 3,000 to 6,000 PSI piezo-resistive silicon MEMS device (PRT). The PRT device consists of 4 resistors connected in a Wheatstone Bridge configuration. It is mounted on a header
with glass feed-throughs for the external connection to the leads of the silicon chip. The header is welded into a stainless steel housing with an isolation diaphragm. The header structure is filled with silicon oil and then sealed. As pressure
is applied against the diaphragm, it is transmitted to the element by the incompressible oil. The MEMs device provides an output proportional to pressure that can be amplified and conditioned by an ASIC inside the sensor body. The structure can be made more robust by adding a pin hole sized snubber of the pressure spikes by providing a restriction followed by an expansion chamber inside the thread in front of the diaphragm. These types of pressure sensor are optimized for pressure
ranges between 1,000 and 5,000 PSI and are appropriate for less price sensitive medium to lower volume applications.

Higher volume and higher pressure applications are serviced by thin film technologies such as those found in the Kavlico P5000 (Figure 2) series. The cross section of a thin film unit is shown in (Figure 4). A stainless steel piece is hollowed out to provide a thin diaphragm and materials are deposited on the top of that piece of steel. Resistors are implanted into the thin film in a Wheatstone Bridge arrangement and the pressure
applied to the hollowed out side of the steel is transferred to those resistors, upsetting the bridge. The thin film elements are welded into stainless steel housings and appropriate signal conditioning is added to complete the sensor construction. It is not uncommon to find thin film elements rated as high as 20,000 PSI which would be impractical in other sensor technologies.

The electrical, temperature and stability performance of the product is defined by the materials used. The unit output is smaller than that of a comparable silicon PRT structure and must be amplified to a usable output voltage range. Nickel
Chromium films are widely used by many suppliers. Newer Titanium Oxynitride (TiON) films used in the P5000 provide almost twice the electrical output per applied pressure as more conventional materials allowing for higher stability underhigh temperature operation.

There is no single best approach for all hydraulic pressure sensing applications. Maximum pressure range, cost targets, physical size, output configuration, safety considerations and temperature range are all factors that must be evaluated in any system design.

For more information contact:
14501 Princeton Ave., Moorpark, CA 93021
Tel: (805) 523-2000 – Fax: (805) 523-7125
Web: – E-Mail:

How Long Should Hydraulic Hose Last?

By Jack Weeks
GPM Hydraulic Consulting, Inc.

How long should the hoses in a hydraulic machine last? Well, the short answer is that it depends. Some people are surprised to find that hose material has a shelf life and that it can be affected by factors such as temperature, humidity and ultraviolet light exposure of the area where it is stored. This differs by hose type and manufacturer of course, but that is not what our customers usually mean when they ask about hose life. When a hose is replaced on a hydraulic machine, we would like to know about how long we can reasonably expect this hose to stay in service.
Unfortunately, hose life can be very hard to predict. There are simply too many variables between machines to make any sort of blanket statement. But if you find yourself changing the same hose over and over again while the other hoses on the machine seem to be immortal, it is definitely time for some further investigation to determine what deteriorating factors are affecting that particular hose and not the others.

Naturally hoses will not last forever. And certainly they will not last as long as hard pipe. Wherever possible, long hose runs should always be replaced by hard pipe, terminating with a length of flexible hose into.components to absorb shock. But some applications demand hoses and we would like for them to last as long as possible. So even if we can't predict hose life with any accuracy, we can at least be sure that we get the maximum possible life from the hose. Here are a few of the most common mistakes we find that can shorten hose life expectancy:

Using the wrong size hose. Sizing the hose is more than cutting it to the right length and putting on the right fitting. Hoses are designed for specific flow rates, pressures and temperatures. If we deviate from their specifications, hose life can suffer. While that statement may appear blatantly obvious, we often find that hose specifications have been ignored - sometimes inadvertently and sometimes deliberately. Most plants stock hose in various diameters but not of different characteristics. Sometimes this one-size-fits-all approach gets us in trouble, particularly when a new machine is installed that requires hose with different specs. The same hose that is used everywhere else in the plant eventually gets used on this new machine with disastrous results. Since there is only one type of hose in stock, no one is likely to check to see if it suits the needs of the machine - it has to, that's the only one we have!

Sometimes the wrong hose is deliberately installed. We have seen hose that is too small in diameter installed in an attempt to make the machine run faster. A common misconception is that smaller diameter hose results in a higher flow rate. Higher flow rate, of course, does increase speed. The problem with this plan is that a higher flow rate cannot be obtained by undersizing pipes or hoses. Hose diameter affects fluid velocity, not flow rate. No matter how small the hose, if you put 10 GPM into it, you can get no more than 10 GPM out of it. Increasing the velocity will however add heat and turbulence to the machine. Not only will this damage the inner metal tube (especially at bends), it can also cause premature failure of hydraulic components in the machine. At one plant, the technician was so insistent that we were incorrect about this that he timed the movement of the actuators in the machine. They did in fact move faster than they had with the correct larger hose. Only once we pointed out that the system temperature had increased by 37oF did he understand the real reason the speed had increased. He could have had exactly the same speed increase (without the additional turbulence) by turning up his oil heater. Yet he was horrified at the suggestion of doing this! As well he should be - whenever the speed of a machine can be increased by raising oil temperature, there is an orifice that can be opened instead. But that's a different article.

Some people over size hoses as well. This in an an attempt to keep fluid velocity and temperature at a minimum. There is merit to this, but also a point of diminishing returns. As long as your hose meets the requirements of the system, you will probably not get enough benefit to justify the cost of the larger hose. Add to that the problem of making a larger hose fit the application, causing bends at the fitting and increasing the chance of the hose rubbing on another surface or another hose and suddenly oversizing our hoses no longer sounds like such a great idea.

Often hoses are cut too long for the application. When we replace a single hose, we want to be sure we have enough hose so we only have to do it once. So the tendency is to cut the hose longer than we need. Thus hoses tend to "grow" over a period of time. In our hydraulic classes, we teach that most hoses (with exceptions of course, such as traveling cylinders) should be no longer than about four feet. But this is not set in stone - by and large, a little common sense can prevail here. Most of the time, if a hose installation looks good, it is good. But if the hose is rubbing against something, snaking around the floor, has unnecessary bends or is jammed into too small of a space, perhaps it needs some attention.

Failing to take into account the abuse a hose will suffer. Hoses are not indestructible. They should not be installed in such a manner as they are likely to be stood on, run over by a forklift or rub against another hose or surface. If subjection of a hose to a hazard is unavoidable, there are many options available to protect it. If a hose must be installed close to a heat source, for instance, a metal heat shield should be installed to protect it. If abrasion cannot be avoided, use a protective cover. Ultraviolet rays from the sun can badly degrade hose material, so if it must be subjected to the elements, protect it.

Just as water and other contaminants in hydraulic oil can damage components, so can they damage hoses. And whenever we have a choice between installing a hose to run vertically or horizontally, the horizontal installation will cause less pull on the hose fittings.

Forgetting about shock spikes when specifying hose. All too often, we have seen hoses installed that are underrated. A machine that operates at 1500 PSI should not have hose rated for only 2000 PSI. It is not uncommon at all for shock spikes to reach several thousand PSI above the operating pressure of a machine. The OEM can recommend the proper hose pressure rating. And if we use the OEM recommended hose, be sure we set the system pressures to the OEM recommendation as well. A pressure setting that is 200 PSI too high will result in shock spike increases of much more than that. Keep shock spikes to a minimum by making sure the pressures are set correctly and keeping components that absorb shock in good repair.

Using an incompatible hydraulic oil. All hydraulic oil is not the same. A wide range of additives is available. Before trying a new oil, be sure to ask your oil vendor if it could damage the hoses.

Neglect. An inspection of all of the hoses should be performed at least monthly. Signs that a hose is about to fail such as bubbling of the outer hose, loss of flexibility, cracks, discoloration or signs of abrasion are easy to spot. It is always better to replace the hose before it fails. If the hose fails during production, not only will production time be lost but it is likely that the ruptured hose will damage something else. Anyone who has ever witnessed a hydraulic hose breaking knows that it is not something to be taken lightly. Tremendous force is released (and a lot of hot hydraulic oil). If your hoses have lasted a year or two, consider yourself fortunate and replace them whether they appear to need it or not. And if a hose is located where someone could be injured or killed if it fails, a much closer change interval is justified.

Jack Weeks entered GPM’s organization in January of 1997 as a CAD draftsman and hydraulic instructor. He has trained thousands of electricians and mechanics in Hydraulic Troubleshooting methods. His computerized animations have made GPM's presentations and training CD's the recognized leader in the industry. He received his education from the Georgia Institute of Technology School of Electrical Engineering and the Department of State Foreign Service Institute. Jack is an experienced draftsman and taught telecommunications equipment operation and repair for the Central Intelligence Agency at American embassies overseas.

GPM Hydraulic Consulting, Inc.
Box 1376
Monroe, GA 30655
(770) 267-3787

Selecting a Pressure Transmitter

Selecting the correct pressure transmitter for the appropriate application can be a complex task, and failure to do so can make the operation of the equipment ineffective and possibly hazardous. Please read below to gain a better understanding of a transmitter’s various components and parameters.

Transmitters can be thought of as electronic pressure gauges. There are two kinds of electronic pressure gauges: pressure transmitters and pressure transducers. The general difference between a transmitter and transducer is the electrical output, where a transmitter outputs signals in milliamps (mA) and a transducer outputs signals in volts (V) or millivolts per volts (mV/V).

The two primary areas to focus on when selecting a pressure transmitter are the operating conditions (environment) and performance requirements.

Operating Conditions
Knowing where the transmitter will be operating in and choosing accordingly the transmitter case and wetted materials will extend its service life. Each transmitter should be selected partly on the basis of the medium being measured. Ensure that the parts exposed to the medium are compatible with or can withstand its particular characteristics.

Keep in mind that heavy vibration, shock, moisture and electric interference will affect pressure sensing. Since each application is specific to a certain set of requirements, understanding the application’s needs will determine the model required.

Extreme temperature ranges can also produce adverse effects to reading accuracy. Make sure you identify an acceptable temperature effect on span (thermal drift) when selecting your transmitter. These can be as low as 0.2% FSO per 10°K.

If the transmitter is installed for outdoor use, ensure that the appropriate type of enclosure/seal is selected. All of Winters’ pressure transmitters are sealed against water and dust entry, and meet standard NEMA enclosure ratings. Standard housing is 304 or 316 series of stainless steel.

Performance Requirements

Is the pressure range being measured in the positive or vacuum scale of measurement? Is each point of measurement stand-alone or are the differences between two points being measured (differential)?

In general, pressure transmitters provide highly accurate pressure readings. It is important, however, to always choose a range that is suitable to your requirements. Consider this scenario: a transmitter that has an operating range of 0 to 200psi and has an accuracy of +/-0.25% is being used to measure pressure on a piece of equipment that only goes to a maximum of 20psi. An accuracy of +/-0.25% over a 200psi range means that the maximum error you may see is +/-0.5 psi. Therefore, for a measurement output of 7psi, the real number may be between 6.75 to 7.25psi. An error of 0.5psi means you have selected a transmitter with an error of 7.14% (0.05 divided by 7) at 7 psi. So, select a transmitter that has the closest normal operating range to what you are measuring, and consider an acceptable accuracy percentage.

Also, be sure about the type of output you need. Winters’ standard transmitter outputs are in milliamps. Output in volts is available.

How Transmitters Work
Power is supplied to the circuit and the flow is regulated.
1. Pressure pushes on a sensor
2. The sensor flexes and changes the resistance or capacitance of a circuit mounted on the backside of the diaphragm (the change in the flow of electricity across the circuit is in direct proportion to mechanical force/pressure applied to the diaphragm)
3. Special electronic circuitry conditions and amplifies the sensor’s signal and converts (transduces) it to a useable signal (i.e. 4-20mA)
4. Electrical output signal is sent to an indicator or computer

Winters Instruments
121 Railside Road, Toronto, ON M3A 1B2
416-444-2345 / 1-800-WINTERS /

Company Continues to Refine Hydraulic Hybrid Drives For Refuse Vehicles

CLEVELAND, OHIO - Parker Hannifin Corporation, the global leader in motion and control technologies, continues to refine the company’s new hybrid drive technology, which is an advanced hydro-mechanical series drive system designed to significantly reduce fuel consumption and increase productivity in vehicles with high start-and-stop applications.

Parker’s hybrid drive system for refuse trucks replaces a vehicle’s conventional transmission with a series hybrid drive system that marries the variable features of a hydrostatic drive, which is ideal for urban routes, with the efficient performance of a mechanical drive that performs best at highway speeds. Coupling this unique hybrid drive system with brake energy recovery technology provides the ideal solution for severe duty applications.

The main benefits of the Parker hybrid drive system are fuel savings, reduced emissions, and dramatically reduced brake wear. Refuse vehicles equipped with Parker’s hydraulic hybrid drive system have achieved fuel savings of 30% to 50% during track testing and actual field trials of refuse collection cycles. Vehicles can utilize full engine power at any time, but the system’s design optimizes efficiency by matching engine load with vehicle requirements. Reduced fuel consumption, a corresponding reduction in emissions, substantially reduced brake wear and improved off-the-line acceleration are all benefits of the Parker hybrid drive system.

Parker’s hybrid drive system is built around the company’s proprietary Power Drive Unit (PDU), designed specifically for high power, high start-and-stop applications. An onboard controller coordinates pumps, hydrostatic motors and accumulators to power the vehicle when in hydrostatic mode during start-and-stop operation while collecting refuse. Instead of solely using power from the diesel engine, accumulated energy from the vehicle’s braking system is stored and used to power the truck each time it accelerates. As the truck reaches highway speed, the PDU transfers from hydrostatic drive to mechanical drive to maximize operational efficiency.

The application of Parker’s hybrid drive system for refuse trucks is an excellent fit. Based on intelligence gathered from refuse companies, fleet owners, municipalities, and original equipment manufacturers, Parker identified the need for improvements in fuel efficiency, emissions, drivability, brake wear, and overall productivity. The new Parker hybrid drive system is tailored specifically to meet these demanding refuse industry needs.

Since the system’s inaugural showing at the 2006 Waste Expo show in Las Vegas, Parker has continued to refine the hybrid drive’s packaging, components, and control strategy to optimize system performance and reliability for refuse collection vehicles. The latest version, featuring an innovative, patent pending design for packaging mechanical, electric, and hydraulic components, will be unveiled at the WasteExpo 2009 Exhibits, June 9 – 11 at the Las Vegas Convention Center, Las Vegas, NV.

Parker’s disciplined, stage gate product development process integrates computer modeling, dynamometer testing, lab testing, and full vehicle on-road operation to validate system performance per customer criteria such as functionality, quality, reliability and added value.

While much of the development and validation of the hybrid drive system is performed within Parker’s engineering offices and labs around the globe, there is no substitute for on-road vehicle evaluation. Currently, Parker is evaluating prototype vehicles through a variety of acceptance tests that replicate real-world operation. A state-of-the-art vehicle proving ground contains all road and driver conditions required to validate vehicle drive performance and durability. Trucks are operated 24/7 in a controlled environment with professional drivers, mechanics, and fleet managers evaluating fuel economy, acceleration, braking, responsiveness, road loads, vibration, gradability, and other conditions that are encountered in refuse collection service.

“Based on the feedback we’ve received to date, we are confident that Parker’s advanced series hydraulic hybrid technology has real potential to significantly improve the fuel efficiency, productivity, and environmental footprint of refuse and similar heavy trucks across the globe,” said Vance Zanardelli, Manager of Parker’s Energy Recovery Business.

In addition to hybrid drive systems for refuse collection vehicles, Parker is also developing variations of the hybrid drive to meet the needs of other on- and off-highway applications. Parker is using the technologies developed for the refuse program as building blocks for configuring solutions tailored for other vehicle platforms with high start-stop duty cycles that also require significantly different torque and packaging solutions. Parker’s broad array of motion and control technologies provides the flexibility required to configure and control these multiple application drive solutions.

For more information about Parker’s Hydraulic Hybrid Drive System, visit

Harvesting the Energy of Leadership and Innovation Within Our Education System.

The Productivity Revolution That Puts People at Center Stage.

By Larry Davis, President, Daman Products

Teaching core subjects in isolation.

As a society, we are not equipping our children with the competitive advantages necessary to prosper in the productivity revolution that is occurring. A revolution that puts people, not equipment, at center stage.

A revolution that can have a dramatic impact on productivity in the private, government, service, and education sectors. This is a process that has emerged in the manufacturing arena and is slowly spreading to other sectors. Ironically, it has little to do with manufacturing.

A number of events have come together to create a conflux of thought on the subject of education, not the least of which are the inordinate amount of time spent in our public schools policing behaviour, and an unacceptable dropout rate. At the heart of the matter are the teaching/training institutions in our society and how they approach teaching: teaching core subjects in isolation. Our schools’ preoccupation with passing state tests is likely exacerbating a singular focus on core competencies. At the technical school level, we teach math, blueprint reading, welding, machine technology, and other technical skills. Our state government, through Workforce Development, provides grant money to industry for teaching these “portable” skills.

These necessary and traditional skills are portable in a narrow sense; however, there is a growing demand for another kind of skill set – skills that are not found naturally in our schools, family units, or traditional business models. These are necessary skills required in addition to core competencies, and in conjunction
with technical skills that will make our society geometrically more productive and competitive as we are progressively exposed to the threats and opportunities of a global economy. The sum of our experiences leads us to ask if we should look internally (within our businesses, service providers, governmental institutions, and educational systems) for answers to our perceived loss of worldwide competitiveness.

In order to set the stage, it is important to explain the context for these thoughts. Our company is what is considered an advanced manufacturing company. To the surprise of many, this does not mean that we are technically superior, or have the best and newest equipment, nor does it mean that we have replaced humans with
robots. What it does mean is that we have redesigned the workflow of our business to move effectively, while we continue to improve the process through iterations and refinements. This may sound logical and not newsworthy. On the contrary, this is unusual and counterintuitive to many institutions. For example, business world fundamentals such as forecasting systems, some business software, cost accounting, and purchasing can actually introduce chaos into operations. Traditional business, education, service industry and government work models are fraught with waste and redundancy because we have been conditioned to work around mistakes and inefficiencies. Most managers will tell you they are glorified “firefighters.” They operate in a reactive mode instead of being proactive. We were in this situation in 1997. The simplified changes we have made since 1997 have allowed us to improve our productivity by 25 percent by making “environmental” changes, with virtually no machine technology improvements.

So what is different if productivity is not the result of conventional technological investment?

For a moment, imagine a work environment in which the “supervised” employees were free to manage their days without supervisory input. They decide who should run which machine, not a scheduler. They are responsible for training new people who join the company, not the training department. They receive material into their work area, not the receiving department. They decide when to take breaks and lunch, not their supervisor. They initiate purchase orders for tooling from the shop floor and virtually bypass the purchasing department, and receive those tools into inventory. They schedule their vacations, not the personnel department. They perform preventive maintenance on their equipment, not the maintenance department. They determine when it’s time to build parts, not someone forecasting product demand. They determine who needs help and provide it, not their foreman. All of these events are doable without the direct involvement of a supervisor or other management personnel. This environment gives people control over their work environment and is the opposite of the typical “command and control” methods of most institutions.

What I have just described is so far from conventional thinking that it may seem absurd. The fact is that this is precisely the path our company chose. It hasn’t been an easy path to blaze, as most of us were not raised or educated in fundamentals that are essential for productive teamwork.

The magic of team competencies.

The magic lies in training our people to work comfortably within teams, to teach leadership and communication skills, and to think creatively. This is certainly easier said than done, but imagine a work environment where people are comfortable leading meetings, using brainstorming and problem-solving techniques when encountering problems, have the ability to reason and find information, and are comfortable giving and receiving feedback. We call these skills “team competencies.” In short, these are simply leadership and communication skills, and affectionately considered “soft” skills. The problem with the term “soft” is that it implies something less important than “hard” skills. I believe they are at least equally important and, arguably, soft skills are more universally applicable and the foundation upon which future competitive advantage will be gained.

With team competencies in place, our people have been given uncommon accountability and responsibility to accomplish their work. We have effectively unshackled their minds and engaged their brains, unlike most traditional operating models where work is accomplished per the boss’ instructions. This new model has been incredibly effective in increasing our competitiveness. Imagine what a 25 percent boost in U.S. productivity would mean in terms of our global challenges.

The value of training in mainstream education.

Here’s the rub: Finding people who are prepared properly for this environment is difficult. Other companies that have made the same improvements state that they will, on average, interview 100 people before finding someone who exhibits the values and traits suitable to this environment. This expends a great deal of time and energy in the hiring process and inhibits companies from keeping up with product demand. Additionally, in-plant training to bring new people up to speed on our methods requires even more resources. We recognize the value of this training and are more than willing to commit to this investment in our new people. But imagine the competitiveness that would result in this country if what we were teaching our people was readily taught in our learning institutions. Instead of this being an anomaly, what if it were part of mainstream education? In my opinion, these types of soft skills are much more valuable to this nation’s workforce. Where welding skills will allow an individual to find another welding job, soft skills will allow people to move in and out of industries.

Imbedding “soft skills” and the need for educational change.

What have we learned? In teaching team and leadership skills, we have found that the most effective method is to relate the training to solving a real problem. Training based on hypothetical situations is most often time wasted. Bringing a team together around a common problem, and introducing techniques to understand and solve the problem, has been powerful. We have seen shift workers, who in the past would not speak to one another, leave a group training session with hope that there was a likely solution. In this setting, the teams had a real need for learning skills, and reinforce the power of those skills by solving their issues.

If this is valuable learning, how do we introduce it into our educational system? We believe it starts with a dialogue, simply suggesting that our current system is in need of change. I can speculate that the change will be difficult and that “teaching a class” in soft skills will not get the job done. Soft skills have to be imbedded in the entire curriculum, and will require major paradigm shifts in teaching philosophy and in the way our educators are educated. A new system would aspire to encompass core skills learning in conjunction with team and leadership building. This may require classes that no longer are identified as “math,” “science” and “history,” but are instead rolled into multidisciplinary classes where teachers work jointly to coach and mentor students as they research subject matter to solve multidimensional problems. We believe that even as our employees are activated and energized by our trust and investment in them, so will our students be engaged when they become active participants in their own education and realize that learning can be rewarding and exciting, as can the workplace. Learning and success can be infectious, and this new approach to education may just be the way to stimulate the process. We have also learned that significant improvement does not happen through an evolutionary process, but instead through the deployment of disruptive technologies or, stated another way, major system change. Nibbling around the edges of our current educational system will, at best, generate incidental change.

As more businesses realize the benefits of abandoning the command and control models, the need for intelligent people with solid team competencies is going to grow. As a society, we are not preparing our children to prosper in this competitive team-oriented business model.

Daman provides outstanding technological and service leadership beyond customers’ expectations in order to promote their interest, thereby ensuring continuous opportunities for Daman employees. This philosophy statement drives the organization. As a result, Daman has developed a solid reputation as one of the best suppliers customers have. Each Daman team member is driven to provide long-term, reliable service that exceeds customer expectations. Daman offers a complete line of hydraulic valve manifold products comprised of two basic groups: Custom Engineered Products and Standard Products. All components are manufactured to tolerances that meet or exceed National Fluid Power Association (NFPA) as well as the International Standards Organization (ISO) specifications. Daman has created a streamlined system for estimating, engineering, and manufacturing Custom Engineered Products from as little information as a hydraulic schematic and component bill of materials. Daman has also developed the most comprehensive catalog of Standard Manifold Products in the world. Our product lines provide every customer with more than one million choices to refine and enhance their hydraulic system, ranging from ISO 02 valve patterns through ISO 10.


Modern production lathes are increasingly being used in place of costlier, more complex CNC machines for many part processing and second operation applications. Advancements in this technology enable production runs numbering in the thousands to be performed more quickly, with less operator skill while offering longer cutting tool life.

The McLean (3) axis production lathe is an example of production lathe design that fulfills this promise. Setup and programmed automation for each job is achieved via a touch screen which can store programs for easy change from one part or operation to another. The McLean system allows each of its optional (3) slide mechanisms to work in virtually any combination to perform grooving, chamfering, boring, drilling and other basic “CNC” type production chores. The slides may be programmed to work individually in any sequence, or any two, or all three to work simultaneously. Each slide is air powered. The feed rate is hydraulically controlled by a Deschner Kinechek® speed regulator incorporated in each slide mechanism to provide precise, infinitely adjustable feed control. The Kinechek hydraulic speed regulator built into the slides on the Mclean production lathes assure the cutting tool will move smoothly while the part is being machined to provide a fine finish and prolong cutting tool life.

The McLean production lathes may be considered as a more affordable alternative to CNC machines for many types of applications.

Contacts: Deschner Corporation
3211 West Harvard Street
Santa Ana, CA. 92704 
T 714 557 1261

Cartridge Style Power Steering Valve (Load Sensing Flow Control Valve)

The power steering valve, which is well known outside the cartridge valve industry, is asimple priority type spool valve, combined with a remote load sensing orifice, used forprecision flow control on demand. Up until recently, all Priority On Demand Spool (PODS) valves were large, heavy, cumbersome, cast iron valves with ports that were fixed in size and location.

In an effort to advance cartridge valve technology, Command Controls Corp. has introduced a small, lightweight, flexible, cartridge style PODS valve, which can be designed into just about any circuit or any size manifold requiring priority-on-demand. This type of valve, even though it has been in use for over forty years, commands even more attention than ever, due to rising energy costs.

The load sensing flow control is used on many applications, especially power steering circuits where priority flow is needed. The valve functions in all systems: open center, closed center and load sensing. It provides flow and pressure to a controlled circuit on
demand. A fluid linked power steering system is used for this illustration, but the same principles can be applied to any circuit requiring a load sensing four-way valve.

A known performance characteristic in both an open and closed center hydraulic system is that the flow rate is affected by the resistance of the load, when a valve is opened to move the load. However, with a load sensing flow control valve, the flow will depend on the amount the valve is opened, independent of the load. By sensing the load, pressure demand is compensated, and the flow rate is actually insensitive to load. Therefore, the flow and the pressure in the controlled circuit, provided by the pump, will only be what is needed to move the load, plus a small amount for control. Any surplus pump capacity is usable in other circuits. In short, a load sensing system provides maximum energy savings.

In a load sensing system, such as the one mentioned above, the load sensing priority valve is typically used to give priority to steering and braking. In each case, the same load sensing hydraulic flow control is used, and the function remains the same. Maximum energy savings can be achieved by using more than one priority valve for more than one stage of priority. This allows for a multi-circuit system with the use of only one pump – a significant cost reduction!

The load sensing, flow control valve can function to build pressure or reduce pressure to the controlled circuit, as needed, in any type of system. It also gives priority to the controlled flow circuit as needed without cutting off flow to the excess flow circuit. The controlled flow circuit relief is set lower than the main system pressure, so that the controlled flow circuit can hold relief pressure, while the excess flow is still available up to the maximum system pressure. The controlled flow circuit relief will also limit the controlled flow circuit pressure, should the system pressure exceed the controlled circuit relief setting. This is especially true in a closed center system, where the system pressure could be set at 350 bar (5000 psi), while the
steering circuit is limited to 70 bar (1000 psi).

Let’s consider the operation with a fixed displacement pump. When there is no flow from the pump, the spring will move the spool to the right until it engages the stop. The “P” port will then be open to the “CF” controlled flow port and the “EF” excess flow port will be closed. Now, consider the controlling orifice closed when the pump is started. Inlet flow will now enter at the “P” port and exit at the “CF” port. However, with the orifice closed, the only open passageway is to the closed end of the spool. The inlet flow pressure will then move the spool against the bias spring until port “EF” is open, and all of the flow will exit at this port as excess flow. This flow will be from port “P” to port “EF” with a pressure drop (rP) of 7,0 bar (100 psi), as determined by the bias spring.

If we want flow in our controlled flow circuit (priority flow), the controlling orifice of the steering wheel is opened. If there is no load (zero pressure) downstream of the orifice, and there is a 7,0 bar (100 psi) pressure upstream of the orifice (determined by the bias spring), then the flow in this circuit will be that which can be pushed across the orifice by a 100 psi delta P.

Now consider that the controlling orifice is open, but the load passageway is blocked downstream. The pressure at port “CF”, 7,0 bar (100 psi), can pass through the orifice, and to the spring end of the spool, to add to the force at the left end of the spool. The spool will now move to the right, to close off port “EF” at port “A”. With the controlled flow circuit blocked, there is no flow across the orifice, and the pilot pressure at both ends of the spool is identical. The spring force will now hold the spool to the right, regardless of how high the pressure rises. As such, the circuit now has priority. Pressure will continue to rise until the relief setting of the pump is reached, and the flow will spill over the relief valve and go back to the tank. There will be no flow at port “EF” and no flow at port “CF” with the circuit blocked. If the controlled flow circuit is not blocked, but is opened to a load that will move at, for example, 100 bar (1500 psi), the action will be the same up to 100 bar (1500 psi). In other words, the 7,0 bar (100 psi), caused by the spring, will pass through the orifice and to the load sense “LS” pilot line to the left end of the spool, and will cause pressure build up until 100 bar (1500 psi) is reached. At this point, the load will start to move. With flow, there will also be a pressure drop across the orifice. The pressure will continue to rise and move the load until the flow through the orifice causes a pressure drop across the orifice equivalent to the bias spring setting, which in this case is 7,0 bar (100 psi). The flow will then level off at this setting, and the pressure will vary as needed.

In the active mode, the spool is balanced between the forces at its ends. Restated, the force of the bias spring must be reacted by the pressure difference at its ends, which is
caused by the pressure drop across the controlling orifice. Load pressure can also act on both ends of the spool, so the difference in pressure caused by orifice, is the only pressure that is effective to control the flow rate. Flow rate in the controlled flow circuit will be according to the orifice area, and the delta P caused by the bias spring regardless of load.

Lastly, consider a load being applied to the Excess Flow (secondary or auxiliary) circuit, while no load, and only flow, is applied to the Controlled Flow (primary) circuit. The flow rate in the primary circuit will be as determined by the orifice area, and the 7,0 bar (100 psi) bias spring setting. When the load in the secondary circuit exceeds 7,0 bar (100 psi), the pressure at the controlling orifice will start to exceed 7,0 bar (100 psi) and the flow rate will tend to increase. However, the pressure at the right end of the spool will also increase, and move the spool to the left. The control has now switched from “A” to “B”. “A” will now be wide open or non-controlling, while the restriction at “B” will reduce the pressure, and consequently the flow in the primary circuit. The pressure and flow in the primary circuit will remain almost unchanged by the loads in the secondary circuit. Any change that occurs will be the result of the difference in the bias spring force, which is caused by the change in length as the spool moves to close off “B”. The spring force changes slightly during all control whether the control is at “A” or “B”. It is important to note that when the load in the secondary circuit exceeds the bias spring setting, which is 7,0 bar (100 psi), the restriction at “A” is very low; it is basically a passageway loss. With a fixed displacement pump and an open center system, this means that there will always will be a 7,0 bar (100 psi) pressure drop from port “P” to port “EF”, but once the load in the secondary circuit exceeds this pressure drop, it is very low, and is on the order of line and fitting losses. Any bank of valves, along with lines, fitting and filters in the secondary circuit, will probably cause a load large enough to shift the spool, and the through flow pressure loss in the valve will be very low as well. If the load in the secondary circuit is high, or the circuit has blocked the pump pressure, it will rise to the relief setting, while the pressure in the primary circuit at port “CF” will still be at 7,0 bar (100 psi). The flow in this circuit will still remain as determined by the spring force and the orifice area, and the pressure and the flow will be restricted at “B”. Or, if there is a load in the primary circuit, the pressure will rise as needed, while the flow rate will be unaffected by the load in either circuit. Note that this same condition exists in a closed center system with a pressure compensated pump, but instead of flow being forced over a relief valve, the pump de-strokes at a high operating pressure. In the area of the load sensing flow control, and in the primary circuit, the operation is identical whether it is in an open or closed center system. The primary circuit also functions the same with a load sensing pump, pressure compensated pump or a fixed displacement pump.

In summary, the advantages of the load sensing flow control valve (PODS valve), when used in a fluid linked power steering system or other similar system are: 1) only the flow demanded by a steering maneuver, by the vehicle operator, goes to the steering circuit; 2) the steering function has priority over other functions in the system; 3) flow not demanded for steering is available to other circuits; 4) improved steering control exists regardless of the steering load pressure; and 5) four sizes are available with regulated flows up to 30 gpm (115 lpm).
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Written by Connie Kosarzecki of Command Controls Corp., Elgin, Ill. Kosarzecki has worked in the fluid power industry since 1958. Command Controls Corp, established in 1993, manufactures a complete line of state-of-the-art, high-pressure (5,000 psi/350 bar), high-performance, screw-in, cartridge-type, hydraulic control valves and manifold systems for the fluid power industry. For more information, please visit

Wide Range Temperature, Pressure, and Fluid Resistant Hydraulic Cylinder Sealing Systems

Joel Johnson Ben Westbrook
Simrit Division of Freudenberg-NOK
Noriyuki Matsui
NOK Corporation

Excessive temperature and fluid compatibility often create problems for hydraulic cylinder sealing. Overall, new materials and designs are necessary to meet the increasing requirements of the industry. Smaller packages with higher pressures combined with hotter ambient temperatures (often directly linked to new environmental standards) continue to drive the demands for better performing seal systems. The new advancements presented in this paper help the fluid power engineer design a more robust cylinder that can be used in a wide variety of applications while providing longer life and lower warranty.

Failure analysis indicates that the main sealing challenges for cylinder makers today are excessive temperature and fluid compatibility (including hydrolysis and glycolosis).
The latest demands (listed below) exceed the capabilities of most off-the-shelf sealing solutions.
•Capable of 42 MPa (6000 psi) @ 0.5mm diametrical extrusion gap
•Handle continuous 110º C or 120º C temperatures
•TR10 of -30º C; - 40º C actual application capability
•Compatible with biodegradable and standard hydraulic fluids
•Hydrolisis and glycolosis resistant
•Retrofit in existing standard grooves

The changes to the temperature range are especially concerning as they affect a broad range of applications. Bench testing has shown that increasing the system temperature by 10º C can decrease the seal life by 5 times (or greater). To narrow the scope of this paper, we chose to use our best-in-class sealing system (fig. 1: buffer seal + asymmetrical rod seal + vented rod wiper) produced in our Disogrin 9250 (urethane) as a baseline.

Baseline Sealing System
This system in Disogrin 9250 has decades of proven field experience, but an upper temperature limit of 100º C and is not hydrolysis or bio-fluid resistant. This paper centers mostly on materials, and will show the results of several new urethane and elastomeric blends in designs equivalent to our baseline sealing system.It should also be noted that many of the results concentrate on the residual interference that remains after test. This is a measurement of the remaining interference the seal
has with the bore and shaft, which takes into account not only wear but also the physical state of the material. This is a strong indicator of remaining life as a design is as dependant upon the material resiliency to ensure that it seals at low (or no) pressure as it is the material strength to ensure that it does not extrude at high loads.

For several years we have supplied a proprietary blend of urethane into the market (NOK U641) that is capable of handling 110º C. As part of the material development, the baseline configuration was successfully lab tested to 500km (0.5million cycles) at 32MPa / 0.4mm/s / 110º C without leakage. Our experience indicates that the results of this accelerated test correlate well with actual field results. In this case the NOK U641 change allows our sealing system to provide similar hours to what was provided by Disogrin 9250, but at an elevated temperature (see figure 2). NOK U641 was also developed to be hydrolosis and glycolosis resistant.

NOK UH05 – 120º C Urethane.
In many cases NOK U641 is all that is needed to meet the application needs. It does not meet our initial high and low temperature requirements though, thereforeNOK UH05 was developed. NOK UH05 improves our cold temperature resistance, while increasing the high temperature capability (see figure 5). The trade off with NOK UH05 is that it is more difficult to process, and therefore only suitable for the thinner cross section of the buffer seal.

ELASTOMERS: G928=120ºC HNBR; A505=110ºC
As a complement to urethanes, we develop specially formulated elastomers for use in pressure applications. The advantage elastomers can offer is that they takeless of a compression set than urethanes (see figure 6), but they require back up support to prevent extrusion at pressures above 12MPa (see figure 7). Lowercompression set equates to improvements in residual interference which is advantageous where longer life is required. Extrusion is not an issue as we have
successfully used filled / reinforced PTFE back up rings to reach 40+MPa.

We have successfully used combinations of urethane and elastomer in Asia for numerous years. A U641 buffer with A505 NBR rod seal system (fig. 8) meets allof the design goals except for the 120º C upper limit (max is 110º C). To meet the 120º C requirement, we substitute UH05 for the buffer seal, and HNBR G928 forthe rod seal.

Immersion testing was conducted for 500 hours at 100º C and 110º C in numerous biodegradable oils to determine their effect on all previously mentionedmaterials. Panolin HLP Synth46 was chosen as our baseline biodegradable oil, and lab testing was conducted on the systems shown in figure 8 at 80º C,100º C, 110º C, and 120º C for 125km @ 42MPa. The results are shown in figure 9. All materials performed well, with U641 starting to take a set at its upper limit of110 deg C (as expected).

The JIS standard groove sizes allow for a back up ring independent of the rod seal material, where as the North American and DIN standard groove sizes do not. Thiscreates a problem with retrofit of the new solutions into existing grooves. We have developed a design that integrates the back up into the seal (referred to as anIUY design – see figure 10) as a solution to this.

The IUY system was tested at 110º C and 120º C for 500km @ 32MPa (0.4mm/s) against a NOK U641 rod seal (both using a NOK U641 buffer), and the residualinterference results are shown in figure 11.

Although neither of the systems actually leaked, the HNBR G928 has significantly higher residual interference overall (especially at 120º) This can bedirectly correlated to longer system life.

NOK U641 is a hydrolisis / glycolosis resistant option for 110ºC systems with standard and bio hydraulic oils provided 100% sealing at extreme cold temperature isnot needed. If 100% sealing at extreme cold temperature is needed, A505 NBR can be used in combination with a back up ring for the rod seal.

NOK UH05 (buffer) in combination with G928 HNBR (rod seal) is a hydrolisis / glycolosis resistant material option for 120ºC systems with standard and biohydraulic oils. The HNBR rod seal does require a back up ring to prevent extrusion though. Base on our testing, this is the best sealing solution for long life atany temperatures.

Field test show that the A505 (NBR) system can go 8,000 hours in and excavator application, and based on the improvement in seal residual interference we expectthe G928 (HNBR) system could last 5X longer even at elevated temperatures. The life of any system is influenced by factors such as contamination, rod damage, and oil degradation which greatly effect seal life in actual applications. Every system should be tested in the actual application.

Standard Design Validation Test Fixture Example


Simrit Division of Freudenberg-NOK,
2250 Point Blvd.,
Suite 230, Elgin, IL 60123

Floating Cage Pressure Controls

Pressure control is a major factor in the design and operation of safe, efficient and reliable hydraulic systems. Limiting the operating pressure to prevent damage to hydraulic components and other expensive equipment due to the resultant forces is one of the most important functions of pressure control valves. Pressure control valves may also be used to control sequence of operations, maintain critical holding forces, and prevent loads from "running away" due to the effects of gravity.

Types of Pressure Controls

Pressure controls are typically 2-way or 3-way valves, which are either normally closed (non-passing flow) or normally open (passing flow). The majority of them are infinite positioning, which means they can assume an infinite number of positions between their fully open and fully closed positions, depending on flow rates and pressure differentials. Some pressure controls are also available as pressure breaker valves, commonly referred to as kick-down valves. These valves are only two position, and are either fully open or fully closed. They open or close at a pre-determined pressure, set by the spring, then reverse their position when pressure to the valve is reduced to near zero.

There are four common types of pressure controls, three of which are discussed in this article: reliefvalves, pressure-reducing valves, sequence valves and counterbalance valves.

Relief Valves

The relief valve is the safeguard that limits maximum pressure in a system by diverting flow back to the tank when the valve’s setting is reached. Relief valves are normally closed, while, in contrast, pressure-reducing valves are normally open. Various types of relief valves include: direct acting, differential area, piloted and bi-directional.

Pressure Reducing Valves

Pressure reducing valves are used to reduce pressure in certain parts of a hydraulic circuit that may not be able to withstand the maximum system pressure established by the relief valve. With a pressure-reducing valve in the system, pressure can be reduced to an actuator downstream of the valve, without affecting the pressure in the rest of the system. Pressure-reducing valves are normally open, and are available in 2-way (non-relieving) and 3-way (relieving) types.

Sequence Valves

As its name implies, a sequence valve causes operations in a hydraulic circuit to take place in a given sequence, without the use of electrical switches and controls. Sequence valves can be normally open or normally closed, depending on the application in which they are used, but are typically 2-way normally closed valves, and are either internally or externally piloted. Some sequence valves are 3-way, and can be normally open or normally closed.

Counterbalance Valves

Counterbalance valves are used when there is a need to control a load. They maintain a set pressure opposite of the load, to keep it from free falling. They may also serve as a full-flow relief valve. Pleaseread our article on Counterbalance Valves for more information.

The Problems

Due to the nature of most cartridge-type pressure control valve designs, they typically require a very precise forming of the valve cavity to ensure reliable operation. If the valve cavity is not machined within required tolerances, the valve tends to bind against the walls of the valve cavity. This can cause distortion of the cage and subsequent valve failure due to binding or sticking of the spool or poppet. Often, the cartridge valve is removed, assumed to be defective, and a different valve is installed in the cavity with the same results.

After a number attempts with different valves it may be determined that the cavity must be reworked to solve the problem. It should be noted, however, that reworking a cavity might also create another problem in that the cavity may become oversized, and will not provide enough squeeze on the o-rings to ensure a proper seal.

Another problem with cartridge type pressure controls is that they are often used in an environment that is prone to significant changes in temperature. This causes thermal expansion and contraction of the manifold and valve parts. Valves with a minimal margin of concentric clearance between the cage and the cavity may function properly with cold oil, but when exposed to hot oil, will experience binding and sticking failures because of the thermal expansion of parts in the hot fluid.

And last, but certainly not uncommon, over-torqueing the cartridge into the cavity during installation is another problem that will cause a valve spool or poppet to stick. Naturally, it is desirable to torque the cartridge into the manifold as much as possible to prevent it from backing out.

The Solution

The patented floating cage concept, designed by Command Controls Corp. of Elgin, Illinois solves the age-old problem of valve spool binding in pressure control valves caused by cage distortion. The floating cage, used in many of Command Controls’ flow controls, allow the cartridge to be flexible enough to conform to the contour of the valve cavity independently of the cartridge valve threads. This allows the cartridge to fit into the cavity without putting any side load on the valve, even in
cases where the cavity may be non-concentric or out-of-round, thereby allowing the spool to move freely without binding. Distortion of the cage, due to the effects of thermal expansion, is also eliminated by the floating cage design.

In the floating cage concept, since the retainer and cage are not physically connected to each other, torque applied to the threads when installing the cartridge in the manifold is not transferred to the cage. This yields another side-benefit: Command Controls floating-cage cartridges can be torqued into manifolds with higher torques than most other cartridge valves, and as such, are less likely to vibrate loose and cause external oil leakage. The floating cage design, along with other unique designs and innovations, put Command Controls’ cartridge valves on the leading edge of cartridge valve technology.
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Written by Connie Kosarzecki of Command Controls Corp., Elgin, Ill. Kosarzecki has worked in the fluid power industry since 1958. Command Controls Corp, established in 1993, manufactures a complete line of state-of-the-art, highpressure (5,000 psi/350 bar), high-performance, screw-in, cartridge-type, hydraulic control valves and manifold systems for the fluid power industry. For more information, please visit

Rexroth Hydrostatic Regenerative Braking System (HRB) Makes Commercial Vehicles Up to 25 Percent More Economical

Rexroth hydrostatic regenerative braking system (HRB) reduces fuel consumption by up to 25 percent and can be retrofitted as an add-on system even in vehicles without hydraulics.

Hydrostatic regenerative braking system (HRB) stores brake energy in a hydraulic pressure reservoir and relieves the load on the main drive when the vehicle is accelerating – potentially reducing fuel consumption by up to 25 percent.

(Bethlehem, PA - Bosch Rexroth’s hydrostatic regenerative braking (HRB) system includes a hydrostatic hybrid drive which uses the considerably higher performance of hydraulics compared with available batteries to substantially reduce fuel consumption even in heavy commercial vehicles.

When the driver presses the brake pedal, a hydraulic unit integrated in the drivetrain presses the hydraulic fluid into a high-pressure reservoir. The resulting resistance makes the vehicle decelerate. When accelerating, the hydraulic pressure reservoir is controlled electronically to release the pressure and it relieves the load on the diesel engine. As a result, the engine consumes less fuel, generates less exhaust gases, and functions more quietly.

The compact Rexroth HRB is ideal for use in various commercial vehicles. The HRB can be integrated and even retrofitted in the chassis as an add-on system, without major modifications.

The system reduces fuel consumption by up to 25 percent in vehicles used for very short distances such as urban buses, garbage trucks, fork lift trucks, or delivery vehicles driven in city traffic. Fuel consumption can also be reduced considerably in other commercial vehicles and trucks used for intercity service.

Each time a driver brakes, the HRB system stores energy which would otherwise be lost. The hydrostatic hybrid drive functions almost maintenance-free and wear-free compared with electric hybrid drives. For example, it is not necessary to regularly change the battery. In addition, the HRB also improves the acceleration of the vehicle. The additional drive energy allows vehicles to be equipped with smaller diesel engines and therefore further reduce fuel consumption and emissions.

All Rexroth HRB components are based on standard components from the manufacturer's current product portfolio. Prototypes of the Rexroth hydrostatic hybrid drive are currently being tested in on-road vehicles.

CONEXPO-CON/AGG 2008 and IFPE 2008
set records for attendance and exhibit space
Construction, construction materials and power transmission industry leaders unveil latest product technologies and innovations

CONEXPO-CON/AGG 2008 and the co-located IFPE 2008 expositions have set records for attendance, exhibit space and number of exhibiting companies. In addition, CONEXPO-CON/AGG 2008 is the largest trade show in North America of any industry in 2008.

CONEXPO-CON/AGG and IFPE are known as global showcases of the latest equipment, product innovations and technological advances for the construction, construction materials and power transmission industries.

More than 144,600 industry professionals from around the world attended CONEXPO-CON/AGG 2008 and IFPE 2008 during their five-day run March 11-15, 2008 at the Las Vegas Convention Center in Las Vegas, USA.

CONEXPO-CON/AGG 2008 covered more than 2.28 million net square feet of exhibits (211,966 net square meters), taken by 2,182 exhibitors, and was 21 percent bigger than the last show, held in 2005.

IFPE 2008 was also the largest in its history with more than 129,000 net square feet of exhibit space (11,994 net square meters) used by 469 exhibitors – a 16 percent increase in space compared to 2005.

International Attendance
A record number of international industry professionals visited the shows – more than 28,000, which is more than 19 percent of total attendance and represents more than 30 percent growth compared to the last edition of the shows. International attendance increased by more than 50 percent from the Latin America and Caribbean marketplace, and doubled from China, India and Turkey. There were also significant increases from Canada, Australia, Russia and the Middle East, to name just a few.

International visitors to the shows hailed from more than 130 non-U.S. countries. There were more than 60 official international customer delegations organized by the U.S. Department of Commerce as well as in-country trade associations and related groups.

Exhibit Features
The show floor included a record number (14) of international exhibit pavilions highlighting products and services developed outside the United States - CONEXPO-CON/AGG 2008 with 10, from Brazil, Canada, China, Finland, Germany, Italy, Korea, Spain, Turkey and the United Kingdom, and IFPE 2008 with four, from China, Italy, Spain and Taiwan. -more-
IFPE 2008 hosted a new exhibit pavilion sponsored by the American Gear Manufacturers Association (AGMA), welcomed back a Power Transmission Distributors Association (PTDA) pavilion, and set up a new pavilion to highlight the expanded presence of sensors at the show.
CONEXPO-CON/AGG 2008 featured a new Safety Zone of exhibits and demonstrations from industry and government groups, including the U.S. Occupational Safety and Health Administration, Mine Safety and Health Administration, National Institute of Occupational Safety and Health, and the Aerial Work Platform Training/International Powered Access Federation.

Education Highlights
The CONEXPO-CON/AGG 2008 seminar program offered a record 130 sessions. Show education expanded in 2008 to include a special seminar on best practices for small fleet management. Also new: select education sessions were offered via LiveCasts and podcasts to extend the value of show education. Education session registrations totaled more than 22,850.

IFPE 2008 also expanded its educational offerings with an electronic controls symposium added to the show’s renowned Technical Conference. The conference offered a record 111 papers from industry experts from around the world. A new IFPE Innovation and Solutions Center, on the show floor, provided real world insights into future design applications. IFPE education session registrations totaled more than 1,700.

Industry Support
The shows were the industry gathering place in 2008. Some 105 allied industry groups were “supporting organizations" of CONEXPO-CON/AGG 2008 and IFPE 2008, bringing their memberships to the shows. In addition to U.S-based groups, these included international industry-related organizations from Brazil, Canada, Chile, China, Finland, Germany, India, Japan, Korea, Mexico, Spain, Taiwan, Turkey, United Kingdom and Venezuela.

A record number of 11 associations held annual conventions or board meetings at the shows, and overall a record number of more than 530 industry-related meetings were held in conjunction with CONEXPO-CON/AGG 2008 and IFPE 2008.

Other Highlights
CONEXPO-CON/AGG 2008 hosted a visit by Admiral Woody Sutton, the U.S. Department of Commerce Assistant Secretary for Manufacturing and Services, on March 12. Sutton toured the show and met with show officials and exhibitors to discuss global trade issues.

CONEXPO-CON/AGG 2008 was also the site of the first ever Construction Challenge competition, initiated by show organizer Association of Equipment Manufacturers (AEM). The creative problem-solving competition was designed to interest teens in construction careers, while calling attention to industry workforce shortages and infrastructure renewal needs.

The next edition of the triennial shows will be March 22-26, 2011 at the Las Vegas Convention Center in Las Vegas, USA. Check online for details:,


Polygon Company, Walkerton Indiana, March 2008

Ever since the inception of composite materials an engineering conundrum has developed regarding the process of how to integrate composites and metals into a working relationship, which benefits upon each constituents performance properties. For composite applications to gain any real traction within traditional metallic OEM markets, a significant bridge needs to be crossed with respect to making them manufacturing friendly within existing metallic manufacturing infrastructures.

Polygon has taken a significant step in that direction through the creation of a composite sleeve inserted within ametallic tube for hydraulic cylinder applications. In addition to this manufacturing friendly concept the added feature of electronic sensing and positioning is included. This new sensing hydraulic cylinder contains a composite/metallic barrel, which can have ends that are attached using existing welding or threading techniques. This patented process allows the composite inner tube to carry almost the entire hydraulic pressure force while the outer metallic tube keeps the structure round. This engineering feat was possible by incorporating the anisotropic expansion characteristics of composites while simultaneously being constrained within the isotropic properties of a metallic shell. The circumferential pressure properties within a composite tube can be altered or manipulated through fiber path geometry.This feature allows the composite tube to slightly expand under pressure, which is in turn immediately contained by the metallic outer structure. It also eliminates the metallic tubing producers concern that the tolerance interface conditions between inserting two tubes together without any machining as a practical impossibility.

A serendipitous side benefit is that now hydraulic cylinder manufacturers can use thin walled, low-grade tubing to
make this technology work. The metallic outer tubing does not have to be honed or plated. Because the composite inner tube does most of the pressure work; low cost aluminum tubing can now even become an option as well. The non-magnetic properties of aluminum also afford new possibilities for additional externally mounted andpre-existing positioning devices to be used. This tube insertion technology is creating new opportunities to attack a very mature market with many new possibilities.

To take this technology to a whole new level is the additional potential of relaying the sensing
signal, via existing asset management or control systems, to a centralized location via wireless access or
even satellite tracking. In real time Polygon can supply this new sensing cylinder technology for
construction OEM manufactures that might have the need for such interpretative data or situational
awareness such as a cylinder requiring maintenance for safety purposes.

The Case for Safety Catchers

Ken Davis, Business Development Manager, Advanced Machine & Engineering Co.

The Europeans have the answer to safeguarding hydraulic and pneumatic presses from catastrophic failure. The good news: now it’s available here in the U.S.

An ounce of prevention is worth a pound of cure…the old adage rings especially true for the thousands of press operators today trying to reduce their production costs and stay competitive with higher speeds, smaller batches and – keep your fingers crossed – greater machine uptime. The cost today for a catastrophic press failure? On the low end, certainly thousands of dollars in lost production time and die replacement costs. On the high end, the loss of a key operator due to injury or a customer that takes his business elsewhere rather than run the risk of falling behind schedule again.

Sure, today’s most modern hydraulic and pneumatic presses have a variety of OSHA mandated protection systems in place to ensure operator safety. Guards, interlocks, electro-sensitive and opto-electronic devices, emergency stop devices and other redundant systems have helped make presses safer in recent years. But when it comes to safeguarding the presses themselves from expensive damage to the press or dies, standards in the U.S. fall well short of their European CEN counterpart, which states in prEN 693 Machine tools Safety Hydraulic Presses: “Where there is a risk…from a gravity fall of the slide /ram a mechanical restraint device, e.g. a scotch, shall be provided to be inserted in the press…On presses with an opening stroke length of more than 500 mm and a depth of table of more than 800 mm, the device shall be permanently fixed and integrated with the press.” A similar CSA Standard (Z142-02) exists in Canada…

‘Faulty’ vs. ‘failsafe’. For most American press operators, however, a ratchet bar, locking bolt or latch is all that’s standing between them and a catastrophic crash should hydraulic or pneumatic pressure be lost suddenly or the lifting mechanism experience a mechanical breakage. When functioning properly, the ratchet system -- usually running the length of the press stroke-- does an adequate job of arresting the fall of the ram and preventing a catastrophic crash. A spring latch will automatically extend to engage the teeth of the ratchet at some point before a crash can occur. Unfortunately, the ratchet is a wear part that after hundreds, even thousands of press cycles can begin to exhibit signs of wear that are difficult to detect visually, and probably can’t be heard, by even the most experienced operator. Over time, the ratchet teeth, spring and latch typically begin to wear, since the spring latch makes contact with the teeth (but doesn’t engage) on the upstroke of the ram every time the ram is raised for the next part. The ratchet, and even the end of the spring latch, can wear to the point where a fall can’t be prevented.

In addition, locking bolts and latches often operate only at the top of the stroke, and ratchet bars at fixed interval positions. Consequently, the ram must often be retracted to its full stroke position each and every part, despite the fact that the part requires only a short opening stroke. This can add considerable, and very expensive, non-productive time to the cycle.

But in Europe, Canada and elsewhere in the world, most presses are equipped with a SITEMA Safety Catcher, which satisfies the requirements of CEN and CSA safety standards, foolproofs presses from a catastrophic crash, and allows the operator to optimize the stroke for any size part. The SITEMA Safety Catcher works a little like the ‘Chinese Finger Trap’ you probably played with as a child. You could easily put your finger in one end of the paper cylinder, but it was very difficult to retract it. In fact, the harder you pulled the more clamping power the simple paper cylinder seemed to exert on your finger. The SITEMA Safety Catcher works in similar fashion. If hydraulic or pneumatic system pressure fails, or if a rope, chain, belt or toothed drive breaks, the SITEMA Safety Catcher prevents the load from crashing down at any position of the descent. Better yet, the system is ‘self-intensifying’, so that as downward force increases, so too does the Safety Catcher’s clamping force.

Here’s how it works (see Fig. 2 and 3):

1) A cylinder rod is mounted to the top of the platen extending through the press crown and the Sitema safety catcher housing (Figure 2). The safety catcher housing is securely fixed to the machine crown / frame and surrounds the rod which is free to move during normal operation. Wedge shaped clamping jaws inside the housing are held with hydraulic or pneumatic pressure to keep the wedges in position so that the rod can move freely.

2) This Safety Catcher instantly becomes effective when hydraulic or pneumatic pressure is lost or released. A spring causes the clamping jaws to firmly contact the rod. As a result, any downward movement of the rod initiates the “self-intensification” feature securing the load.

3) Significantly, the energy of the falling or sinking load is used to apply additional clamping force if needed. In other words, ‘self-intensifying’ friction created between the clamping jaws and the cylinder rod draws the jaws into their maximum clamping position after only a few millimeters of movement.

4) If the load continues to increase, the Safety Catcher will continue to hold the rod in a fixed position until a pre-determined static holding force limit is exceeded – (approximately 3-4 times the retain force). Beyond that point, the Safety Catcher continues to safely hold the rod, with a braking action dissipating the kinetic energy of the falling mass while it continues to resist the downward movement of the platen.

5) Only when hydraulic or pneumatic pressure is restored in conjuction with the equivalent reverse movement of the rod are the clamping wedges released, making the SITEMA Safety Catcher inherently failsafe.

SITEMA is ‘catching on’ everywhere. From presses to large hydraulic elevators to stack loaders to machine tools – in almost any application where a large load is traveling and the potential for a catastrophic mechanical failure exists – SITEMA Safety Catchers have been applied successfully and in increasing numbers, as safety standards toughen around the world. They are available in a variety of sizes to meet most common press sizes, including the very largest. Most importantly, they are readily available today in the United States through Advanced Machine and Engineering Co.

About AME

AME is a global manufacturer and distributor of precision machine components, fluid power components, fixturing/workholding, power drawbar and spindle interface components, and saw machines and blades. The company also designs and builds special machines for a variety of industries, and provides machine rebuilding, retrofitting and contract manufacturing services. AME has partners and customers around the world and across the U.S. To learn more, visit

Bob and Dan's "boring" adventure

Cutting two eight-mile subway tunnels through varying Santa Monica Mountain rock formations is a dirty business. But someone had to do it.
Construction & Tunneling Services, Inc. (CTS), Kent, WA, an established design engineer and supplier of mechanical excavation equipment for the construction and mining communities, has kept two tunnel boring machines (TBMs) over 25 years old in service with the help of Bosch Rexroth.

The two TBMs were used by specialty underground contractor Traylor Bros., Inc., of Evansville, Indiana, on the Red Line Metro project owned by the Los Angeles County Metropolitan Transport Authority.

The Red Line Metro project required the construction of two 12,500-meter subway tunnels traversing the Santa Monica Mountains near the famous Hollywood sign. The final tunnel was a cast-in-place concrete lining of 5.44-meter diameter, so the job required two tunnel boring machines with a bore diameter of 6.3 meters.

CTS had to engineer and remanufacture two existing TBMs, resizing them with new cutterheads and shields and adding a hydraulic drive, taking advantage of Bosch Rexroth's broad technical product line.

"Hydraulic components consisting of pumps, motors, and valves were integrated with custom gearing and specialty hydraulic cylinders to provide the bulk of the critical pieces that the tunnel machine requires to operate at its peak," said Dan Nowak, CTS president. "Our experience with this job reaffirmed what we have known from previous work with Bosch Rexroth - they make good products that fit in major areas of machinery design, they understand how these parts perform and where they should be applied for best results. I don't think you will find an operating tunnel machine that doesn't have a Bosch Rexroth part on it."

The job was not without surprises. The first reach of these tunnels traversed soft rock, then encountered a soil-like material, almost plastic in places. Other materials included squeezing shales, sandstones, conglomerates, and granodiorites.

"The opinion of both the operating contractor and the CTS staff at the end of the job was that without the variable speed features and the higher torque capacity offered by the Rexroth hydraulics, the project would not have had such a mechanical success," according to Nowak.

If you've got a mountain of dirt to uncover and an unyielding deadline to meet, talk to the people with big ideas and the brawn to back them up. Bosch Rexroth.

Bosch Rexroth Corporation
2315 City Line Road
Bethlehem, PA 18017-2131
Telephone (610) 694-8298
Fax (610) 694-8339

When Morrell Inc, Schuler Inc and Bosch Rexroth teamed up, they proved that global manufacturing of auto parts with local control in Michigan was the right path for helping the Big Three achieve more productivity.

The world's first crossbar transfer press, developed by Schuler AG, in the early 1990's, revolutionized auto parts stamping plants throughout the auto industry.

Today's compact crossbar transfer press is used not only for large unstable auto body panels, but also for production of mid-sized parts such as doors and engine hoods.

Through the use of a compact transfer press and the unique partnership of Morrell, Schuler and Bosch Rexroth, both Ford Motor Company and General Motors are able to produce new hoods and doors while improving productivity, design flexibility and a reduction in costs.

Critical to the success of this global-local team effort was the teams ability to meet the scrutiny of design engineers in Germany, while also providing local installation and testing in Auburn Hills, Michigan. Schuler was also able to work with a single rep for all technologies while supplying contact for everyone.

If you would like to forge an application engineering partnership, across technologies, continents, companies, Bosch Rexroth can help.