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    Very often I get to see the following situation- a hydraulic machine has a problem, normally the "not enough force" problem. A series of troubleshooting attempts are made, leading to the final "it probably is the pump/it must be the pump/there's a chance it is the pump" conclusion (it can also be the "motor" variant). Then, as no "advanced" testing gear is available, the aforementioned pump is dismounted from the rig and is brought over to a local workshop for a check-up. At that point, as the troubleshooter is not a hundred percent sure that the pump is the root cause of the evil, he decides it is best to test the pump in the workshop test bench first, which sounds like a logical choice. Indeed, it is a quick way to make sure the diagnostics was correct, and if the pump turns out to be OK, having it on the test bench is a good way to make all the adjustments, if necessary.

     Most of the hydraulics workshops will be happy to test a pump for a client, charging a not so modest fee, of course. For them it's a win-win, if the pump is OK, they'll charge the test, if it is not OK, they'll charge the test and the following repair, and another test in the end. The bottom line here is - in any case they get to charge something.

    A smart mechanic, however, in such situation, before blindly agreeing to shove a pump into the test rig, will perform three simple checks, which, if failed, will guarantee that consequent tests are a waste of time.

    Number one - rotate the shaft test. You take a necessary tool, most of the times a pipe wrench, and rotate the shaft a couple of turns. An experienced mechanic will easily detect jerky torque resistance or excessive play/vibration - sure symptoms of serious failure in the rotary group or the bearings.

    Number two - air in the pressure line (open circuit), or pressure lines (closed circuit) test. You take an air gun, improvise some kind of a sealing accessory (a piece of cloth) and blow compressed air into the pump's inlet. If there is a serious damage to the rotary group, causing excessive internal leakage, it will be easily detected by the generous quantity of air passing through to the case drain port or suction port (or the opposite line of the closed loop pump). Some previous experience might be needed to determine how much exactly is "generous" for a certain pump model. Of course, in case of a vane pump this test is useless.

   Number three - flashlight test. You take a small LED flashlight, and peek inside the casing through the case drain ports. Any signs of metal wear, like chips, raspings, shavings and other wear, like shamelessly broken parts staring at you, are all tell signs of a busted pump.

    These three simple tests take under a minute to perform, and are a fast way of detecting damage without performing any hydraulic tests. For example, let's imagine that the pump you are about to test has a valve plate like this. In this case you won't detect any uneven or excessive torque resistance on the shaft, nor will find noticeable wear debris inside the casing, but you will see a large amount of air passing through the pressure line to the casing, something a pump in a good condition wouldn't allow!

   Unfortunately, these three very simple one-minute checks are often overlooked, which at some occasions leads to downtimes, that could have been avoided.

    This is just another reminder that no matter what a system or a component you are troubleshooting, you should always perform simple checks first. A few extra minutes you'll spend doing so can potentially save you many hours of work!


    Of the above three, the air test is my favorite. In fact, knowing how to correctly use compressed air to test hydraulic components can potentially save you a lot of time. Most importantly you MUST know exactly where to blow and what to expect. "Mastering the air gun techniques" allows a technician to detect some malfunctions during disassembly of a component (this is especially true in case of displacement controls, like checking the correct function of check-valves, shuttle valves, existence of oil passages, etc..) which in turn  speeds up the whole repair process, eliminating the need of faulty component disassembly during "wet" tests.