The smart way to troubleshoot hydraulics

Print page

Email page

By Steven P. Thomsen, P.E.

PlantServices.com

Keywords: "chronic fluid"

Plant managers, building engineers and project managers have an inherent stake in the productivity and health of their hydraulic equipment. When there’s a recurrent or chronic problem, it’s imperative to have background information or, better yet, a strong suspicion of what’s wrong before the service providers, inside or outside the company, are called.

Plant managers, building engineers and project managers have an inherent stake in the productivity and health of their hydraulic equipment. When there’s a recurrent or chronic problem, it’s imperative to have background information or, better yet, a strong suspicion of what’s wrong before the service providers, inside or outside the company, are called.

You don’t have to be a technocrat to analyze the current and past performance, maintenance information and failure data. Probable cause and direction determination isn’t a lengthy, time-consuming endeavor -- it doesn’t take long to narrow and focus the effort put forth by the troubleshooters. In addition, it’s smart business to be an informed consumer.

Too often, machine repair adopts the shotgun approach to troubleshooting. I was involved in a machine repair fiasco when a storage and retrieval machine that ran back and forth on a rail wouldn’t move. I was called in after two days of intense shotgun troubleshooting resulted in replacing the logic backplane, the 480-VAC motor and all the associated AC controls. The only thing left for them to replace was the wiring harness, which they were eyeing with great suspicion. Why no one pulled out a meter and looked for a more likely cause I’ll never know. It turned out that mechanical failure of an interlock contact in the forward circuit was keeping both forward and reverse contactors from energizing.

On the hydraulic side, it’s a cavitation problem that comes to mind. A pump on a machine was making a horrendous noise even after it had been replaced. The machine wasn’t functioning properly and the symptoms were the noise and the machine slowing to a crawl. A little common sense here may have avoided the expense and downtime associated with the pump replacement.

Cavitation is a vapor pressure phenomenon that produces tiny bubbles in the fluid, usually at the business end of a hydraulic pump. The bubbles implode and pit the metal impeller vanes, gears or pump housing. The result is premature wear that can occur in a very short time. Two possibilities should jump out at you right away: low fluid in the reservoir or a restriction in the fluid path that starves the pump. In this case, the intake strainer was partially blocked with debris (a piece of a rag) and the pump wasn’t getting the flow it required.

Diagnostic ports

I believe very firmly in watching and listening to a machine when it’s healthy because you’ll be receptive to it telling you a lot when it’s sick. If your job function doesn’t allow you the luxury of taking some time to be around your healthy machines, do the next best thing and talk to those who spend all their time with them. Operators with or without mechanical knowledge usually can give you volumes of data and direct observations that contain links and clues to the problems at hand. In addition, the day-to-day mechanical crew can provide a wealth of valuable information. Also, I’m a huge fan of test ports that accept a pressure gauge to permit monitoring key locations in the hydraulic circuit.

Ask your service team if the machines have enough test ports. If the answer is negative, add them during the next routine shutdown to provide valuable information in the unlikely event of a system failure. Then, gather pressure readings from each port during production and record the results along with temperature.

The following list of suspects suggests some common hydraulic problems and their root causes. Using them might help discover a solution. At the very least, they might provoke thought and direction that will lead you to a happy ending.

Suspect 1: A precipitating event

The first step in any troubleshooting routine is analyzing the last thing(s) that happened to the system before it began to fail. There’s almost always a single event that’s connected in some way and leads to the failure source. It might appear unrelated, it might have a fairly significant time lapse, but it can be proven to be directly linked to the failure. Look for a seemingly benign maintenance procedure, part replacement, preventive maintenance procedure, factory upgrade or the like. Ask the operator, maintenance personnel or anyone else who might have been involved with the equipment. Record the events for analysis, and document to the best of everyone’s recollection and from maintenance records exactly when the events occurred.

Retreat to a quiet area with your findings and look for an event or a trend. It might reveal a directional clue or perhaps a mistake that could have led to an inadvertent problem. Perhaps the replaced component wasn’t the correct part. Compare part numbers on the old and the new part. Perhaps the installer used Teflon tape (a definite no-no for hydraulic systems). Kinked hoses, pinched hoses or kinked lines are other possibilities. Verify that pressure readings on the machine gauges are what the OEM intended. The adjustments on the machine may have been manipulated incorrectly. Set-up procedures might have been skipped or performed improperly.

Suspect 2: Filtration

Look for signs of improper or inadequate filtering. Check the OEM’s filter change schedule and ensure that the recommended filter type was installed. The filter change might have introduced contaminants. Dirt or machine debris, including product or product waste, may have entered the system. Verify the filter rating for flow and filtering particle size meets OEM specifications. Verify that the strainer is clean. If someone added fluid to the reservoir, confirm that it was the correct fluid, not just something that was in the shop at the time.

Suspect 3: Contamination