Overview
A hydraulic pump can be put through a variety of tests to determine its state. The temperature of the pump case, the flow of the case drain, and the current draw of the drive motor are all standard checks that may be performed on a hydraulic pump regularly and overtime to monitor wear.
The bypassing rises as a pump’s internal tolerances grow, and the more it bypasses, the hotter the pump casing becomes. Pump case temperature is determined by pump wear, and case drain flow is the same way.
Of course, there are basic standards, and hydraulic power pack manufacturers‘ literature may help you get a sense of acceptable settings, but what is usual for one machine may not be for another.
While these inspections should be regularly and documented for future reference, most industrial operations do not retain such records. In many situations, even when adequate records are saved, all you have is a calculated likelihood of the pump’s condition. You can compare test results over time, but you won’t know for sure until the pump is replaced and the symptoms go away.
Testing Hydraulic Pump
Changing a pump when there is a loss of production is time-consuming and costly. However, if the system is built up for it, one test can be performed to identify whether a pump is excellent or defective in less than a minute. Most procedures, however, aren’t.
Even a poor pump will provide all or almost all of its flow if it encounters little or no resistance, but only a good pump will deliver its rated flow at normal system pressure. According to hydraulic power pack manufacturers, measuring the flow via the system relief valve is the easiest way to figure this out.
A flow meter may be permanently placed in the system for a few hundred dollars to monitor the flow through the relief valve whenever you want to know the pump’s status. When the system is functioning well, this may appear to be frivolous. After all, the flow meter might stay in the system for years without being read.
Likely, no one will ever examine the meter as long as the system is generating correctly. When the system goes down, though, and you’re faced with hours of costly downtime while trying to figure out what’s wrong, you immediately wish you had a better approach to diagnose a problem.
Most industrial operations save enough money the first time a pump isn’t changed unnecessarily due to having a flow meter in place to test it. The price of several of these pumps is exceptionally high.
They may cost anything from $4,000 to $40,000, and sometimes even more. Saving a few hundred dollars on a new automobile by looking for one without a speedometer or a temperature gauge is akin to saving a few hundred dollars on a new car by looking for one without a speedometer or a temperature gauge.
Depending on the hydraulic pump’s design, the flow meter can be installed in either the pump’s pressure line upstream of the relief valve or the relief valve tank line. Because the meter used in the relief valve tank line may be rated for lower pressure, a flow meter in the relief valve tank line is the less expensive alternative.
Unfortunately, many systems lack an exposed tank line for the relief valve. In this scenario, a high-pressure flowmeter must be put in the pressure line between the pump and the relief valve. Flow-through the relief valve may be monitored on the meter when the system power source is disconnected from the rest of the machine.
Close the isolation hand valve to stop the flow from the system, leaving just the relief valve as a flow channel to the tank if you’re using a fixed displacement pump system.
Turn on the system and take a flow reading with the relief valve set to external pressure. Even if the pump is broken, it should still produce the complete or almost total rated flow. Begin increasing the pressure adjustment while keeping an eye on the flow meter.
There is no doubt that the hydraulic pump is good if you can increase the setting to normal system pressure without a noticeable loss inflow.
Your issue is with something else. If, however, the flow on the flow meter declines as the pressure on the relief valve increases, the pump is faulty and has to be replaced.
Hydraulic power pack manufacturers: Turn the compensator adjustment entirely clockwise before beginning a pressure compensating pump system.
This will cause the pressure compensating pump to act like a fixed displacement pump, delivering its total flow volume at all times and preventing de-stroke throughout the test. Before beginning the machine, make sure the relief valve is set to external pressure, regardless of the kind of hydraulic pump!
Then do the test as if you were using a fixed displacement pump. Measure the flow with the relief valve set to the lowest setting. Raise the relief valve’s pressure setting while keeping an eye on the flow meter. You can be assured the pump is working if the flow stays constant up to normal system pressure.
Steps for Testing hydraulic pump
- Except for the system relief valve on a fixed displacement pump, disconnect all components/hoses from the pump discharge port.
- Connect the test flow meter to the pump’s discharge.
- On the test meter, fully open the flow control valve.
- Turn on the engine or motor that drives the hydraulic pump.
- Look for any leaks.
- Keep track of the pressure and flow.
- Slowly close the flow control valve, causing the pressure to rise.
- In 500-psi intervals, record the pressure and flow measurements.
- Take more readings in smaller increments as you come closer to system pressure (maybe as little as 50 psi).
The Results and Their Interpretation
If the tested values match the satisfactory levels as told by your hydraulic power pack manufacturers, your pump and relief valve is in good working order. Connect the rest of the system after disconnecting the flow test meter. The source of your issue is elsewhere in the system.
Even if your results do not match the acceptable ranges, the pump may still be effective. There is a relief valve in the system in both situations, and a compensator on the variable displacement pump might also cause problems.
