parameters to test a hydraulic pump

Written by Camilo H Rueda Friday, 13 April 2012 13:10

Questions & Answers - Hydraulic Pumps

Whether the pump is newly assembled, repaired recently or even is still mounted on the machine, it must be tested

to confirm it will work according to the manufacturer's specifications.

The pump being the first element to receive the power to be transmitted, its performance must be optimal and in accordance with the operating features provided by the manufacturer.

The general idea is to test the pump duplicating the test originally made by the manufacturer in their facilities. It must meet several minimum conditions such as oil temperature, speed of rotation of the drive shaft, type and viscosity of the oil or fluid used.

The temperature and viscosity of the fluid is critical for testing different values ​​can lead to erroneous results or very different. If the viscosity is lower than the value suggested by the manufacturer for testing, the volumetric efficiency may be lowerso the pump may be rejected. The speed of rotation is also critical to test the pump because the outflow of the pump varies according to this. That's why you must use the same speed used by the manufacturer.

According to the chart, we see the loss of flow (5.3 GPM) due to the inefficiencies of the pump with a flow of 108 GPM @ 1800 RPM, 5000 psi. Which gives a 95% volumetric efficiency. The temperature and viscosity of the fluid for the test was 122 ^oF and 160 SUS respectively.

Depending on the type of pump, the testing procedure will vary. Next we show the procedure for testing fixed displacement pumps, variable flow with compensator single, with other types of compensators and load sensing, external pressure, hydrostatic transmissions and others.

Elements that we must have on hand for testing.

1. Graphics and manufacturer's specifications, such as flow @ rpm, maximum pressure, volumetric efficiency @ maximum pressure or flow, temperature, viscosity

2. Flow Diverter valve (ball valve)

3. Adjustable relief valve

4. flowmeter

5. Pressure Gauge

6. thermometer

7. tachometer or RPM meter

Fixed displacement hydraulic pump test.

Generally, the manufacturer supplies the pump flow at a certain speed (RPM), for example: 1200 RPM or 1800 RPM or flow graph against RPM. Take two values ​​of flow, one at 0 psi and the other to the maximum pressure, for example, 2000 psi, 3000 psi to 5000 psi, etc..

hydraulic fluid should be preheated to the test temperature which is usually at 40 oC. with viscosity ISO 32. This temperature must be kept constant throughout the duration of the test for consistency.

Before starting the power source, it is important to ensure that the suction of the pump is free and open to the tank and besides, you have the right size. So the diameter of the pipe or hose used is no less than the diameter of the connection of the pump. Moreover, it is important to ensure that the discharge of the pump has a diameter greater than or equal to the connection thereof. Finally. make sure the bypass valve is fully open and relief valve setting in its minimum. This last because in the first start, the pump discharge should have absolutely no obstruction or pressure to overcome to avoid premature pump damage due to lack of lubrication during the first few seconds. This helps to expel the air trapped in the pump discharge and the line to the relief valve. The vane and piston pumps are particularly sensitive in this regard, the gears are not so.

After starting, you should reach the ideal value of speed (RPM) according to the manufacturer. After a couple of minutes that the lines are filled with fluid, you must close the bypass valve. You should see now the minimum value adjustment relief valve (150 - 300 psi).

Take the measurement of pump flow and save or write down the following: GPM, RPM, PSI and oF. Below rises gradually adjusting the relief valve to increase the pressure to the maximum. Then lower the setting to the minimum and repeat this cycle several times. Then, leave the maximum pressure and take the data back: GPM, RPM, PSI, oF.

Note: The values ​​of RPM and F (temperature) should be very close if not equal to those taken with the minimum pressure.

Now, perform the following calculation:

Ef vol = GPM (Pmax) / GPM (Pmin) x 100%

Compare this value with those supplied by the manufacturer. If these are not available, one can assume that if the volumetric efficiency is above 95% the pump is in optimal working conditions as a new pump. If the values ​​are between 85% and 95% in most cases and depending on the application the pump is still acceptable for the job. It should be noted that if the machine is a high production, 5% or more of inefficiency is that much less of production which may represent a large amount of money lost, hence the importance of maintaining the pump in good condition. If the efficiency is less than 85%, only in some applications may be acceptable in most of those pump should be discarded or repaired.

Finally, you must check that the pump has no external leakage. This is achieved by performing work cycles between maximum and minimum values ​​of pressure combined with long periods of work to the maximum.

The duration of the test may be of 1/2 hour to 1 hour or more as needed.

It should be noted that once it is verified that the volumetric efficiency is acceptable and before performing the leak test, the pump, and the suction and discharge connections should be cleaned up carefully to detect even the minimum leak. You can use optical equipment leak detectors that work by adding fluorescent liquidto the  oil of the test machine. They show with the use of special glasses even leaks that are invisible to the naked eye.

Wait for the variable displacement pump test report...soon.