Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1222953
www . machinerylubrication.com | March - April 2020 | 17 3. Make the Easiest Checks First Once you have traced the flow on the schematic, identified all the components that could cause a pressure problem and isolated the power supply to determine which part of the system has the problem, start making checks. List the suspect components in order of the easiest to the most difficult to check and make the easiest checks first. I have frequently seen people make the mistake of going immediately to the worst-case scenario, spending hours and large sums of money to replace very expensive components only to find that they were not the cause of the problem. In almost every troubleshooting class I teach, someone relates a story of a time when they thought they had a major high-cost component failure but eventually found the problem to be a stuck check valve, hand valve that had been left open, blown fuse or some other simple thing that they had missed. ink back over your career. Isn't it usually the simple things that fail? Try the easy checks first and work your way to the hardest. Even if it does turn out to be the big component, not much time will have been lost on the simple things. In the previous example, let's assume no change in pressure was observed by isolating the power supply, suggesting one of the power supply components to be at fault. In this system, there is a suction strainer, pump and relief valve. Any of these components could cause a loss of pressure. Is there a whining sound? If so, perhaps the pump is cavitating. e most common cause of cavitation is a plugged suction strainer. e suction strainer typically is inside the reservoir, below the oil level, out of sight and out of mind. It isn't checked or cleaned as regularly as it should be. Of course, the pump cannot deliver more oil than it can take in, which can result in reduced flow. Sometimes the flow can be dras- tically reduced. is often will occur gradually with the increase in sound corresponding to reduced speed, but it can also happen suddenly if a large amount of sludge is stirred up by turbulence in the reservoir. Usually, it only takes a few minutes to check by pulling the suction line and inspecting the strainer. If it is blocked, it can be cleaned with compressed air. If there is no whining sound, check the relief valve. With the system deadheaded, try to adjust the relief valve. If it will not adjust, chances are it could be stuck open. Bleed down any residual pressure, lock out the system and pull the relief valve. Look inside for trash, bent or broken springs, excessive wear, or anything that could keep it from seating properly. Pay particular attention to orifices. In one case, the relief valve had been pulled and checked prior to my arrival. I was told that they had found two orifices, but both were clear. I asked that they pull it again so that I could check it myself before we eliminated it as the problem. Sure enough, there was a third orifice that they had not seen, and it had a small piece of debris, perhaps the size of a grain of sand, lodged inside. We cleaned the orifice, reassem- bled and reinstalled the relief valve, and the pressure came back up to normal. e final possibility in the power supply is the pump. In the example system, a fixed- An example of a typical schematic for a hydraulic system. A suction strainer typically isn't checked or cleaned as often as it should be. A schematic with a flow meter installed in the relief valve tank line. ML