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Monitor could prevent hydraulic failures

Monitor could prevent hydraulic failures

Rochester Hills, MI--For users of construction equipment, it's a nightmare: A hydraulic pump on an excavator comes to a screeching halt, and a construction team sits idly while a maintenance worker replaces the pump. Ultimately, the contractor ends up losing tens of thousands of dollars while awaiting repairs.

An isolated incident? Hardly. Every day, hydraulic failures occur in machinery around the world. In the process, those failures cripple countless construction projects and industrial operations.

Ironically, the culprit behind many of those failures is contaminated hydraulic fluid. Though it may seem improbable that tiny contaminants can cripple huge machinery, experts say it's the number one cause of hydraulic failure. By some estimates, between 70% and 90% of all such failures are caused by contaminated fluid.

Soon, however, equipment manufacturers may have their strongest weapon yet in the battle against contamination-based failures. An in-line monitor, developed by engineers at Vickers, Inc. (recently acquired by Eaton Corp.), will fit across a hydraulic pressure line, near the pump outlet, and will continuously monitor the condition of the fluid flowing through the line.

By employing the original equipment's existing microprocessor, the system could be programmed to sound an alarm when a certain contamination level is reached. Or it could even shut the equipment down to prevent damage in case of an emergency. "Ideally, it could give you a continuous reading, and maybe even predict a failure before it happens," notes David C. Downs, global product manager for Vickers' ProActive Maintenance group.

Unobtrusive design. Known as the Fluid Specification Monitor, it works by "watching" for scattered light in the fluid stream. To accomplish that, it employs a light emitting diode (LED), a light trap, collector lens, photodiode, and amplifier. During regular fluid flow, the LED shoots light through the stream to the light trap on the other side.

When the fluid in the line is clean, the light travels straight through the fluid to the light trap on the other side. But as the number of particles increases, light bounces off the particles. Scattered light is collected by the collector lens, then measured by the photodiode. Therefore, the greater the amount of scattered light measured by the system, the dirtier the fluid.

Fluid Specification Monitors could 'watch' fluid cleanliness on various hydraulic circuits around a machine. Big construction machines often have 10 or more circuits, each of which would need a separate monitor.

Output from the system can be analog or digital, depending upon the application. That way, the Fluid Specification Monitor can send a signal to an OEM computer, or to an analog dial display.

One of the keys to the system is that it is absolutely unobtrusive. The LED, along with a beam splitter and aperture, are located in a small enclosure on one side of the pressure line. Light from the LED is projected through a pair of synthetic sapphire windows on either side of the line. Another enclosure on the other side of the pressure line contains the collection lens, photodiode, and amplifier. Because both electronic modules are located outside the pressure line, it doesn't restrict the flow of fluid.

Broad impact. The constant presence of an in-line monitor is expected to be a huge step forward for manufacturers of industrial and construction equipment. "Contamination is one of the biggest problems in hydraulic machinery," notes Kevin Klein, director of research and development for Gomaco Corp., an Iowa-based manufacturer of construction equipment. "So if there's a way to monitor that contamination and head off trouble before it happens, it's definitely worthwhile." Klein adds, however, that the system's cost will be the key to its success. At the very least, he says, it must cost no more than the warranty cost of the equipment it protects.

An LED in the monitor projects light through a window in the pressure line. A collector system on the other side measures scattered light. The more light it measures, the dirtier the fluid.

Because beta-test versions of the Fluid Specification Monitor have yet to be released, however, Vickers does not yet have an exact price for the unit, but is estimating that it will cost about $1,000. And, as is true with so many other electronic products, Vickers executives expect costs to drop as production volume rises.

Up to now, the best systems available for fluid monitoring were portable particle counters, which typically cost between $8,000 and $16,000. In most cases, users employed the portable counters every month if they suspected the fluid was dirty, or every six months if they believed it was relatively clean, Downs says. In between those times, they had to hope their fluid didn't get unexpectedly dirty. "That can be a risk," Downs says. "Especially if you've got a high-priced machine that's critical to your operation."

Recent developments in hydraulics now make it all the more important to monitor fluid cleanliness on a more frequent basis, Downs says. Today's hydraulic systems tend to be more sensitive than the hydraulic equipment used a decade ago. "Low pressure systems with bang-bang valves were very forgiving," Downs says. "But when you get to modern systems--like plastic injection molding machines that run at 3,000 psi with piston pumps and proportional valves--you need much cleaner fluid."

What's more, new construction and agricultural machinery represents a larger investment for the user. With costs rising, original equipment manufacturers are learning that users are less tolerant of failures--hydraulic or otherwise. "Our customers are demanding longer times between failures," Downs says. "Eventually, we expect them to reach the point where they build the machine, button up the hydraulic system and never open it again."

For that reason, Vickers engineers expect their new technology to be integrated into pumps and valves in the next decade.

For now, the firm is planning to make the technology available to select customers for field testing by the end of this year. Knowledge gained from those field tests will help Vickers engineers customize the systems for customer applications. Says Downs: "The goal is to help customers improve their fluid cleanliness levels so that contamination will never be the cause of system failure."

Typical Applications

  • Excavators

  • Motor graders

  • Plastic injection molding machines

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