Written by Camilo H Rueda Wednesday, 21 September 2011 20:05
From experience we can say that in general, the hydraulic component on which the greatest responsibility for the functioning of the hydraulic system of a machine is the pump, or pumps.
This does not mean that it is the most important, is generally the one that works longer, and because of its construction is highly dependent on the good care of the oil and a good filtration.
All hydraulic systems follow a logical sequence of operations determined by the type of components within the circuit and how they are interconnected. Without going into details of how they made the detection of faults in the machine, say we have a suspicion that the pump may be malfunctioning.
Before you begin, you must obtain as much information about the system and in particular about the pump:
Type of prime mover (electric, hydraulic, diesel, gasoline, etc..), Power and rotation speed or RPM. The temperature at which the system works.
Type of pump (gear, vane, piston, etc.) Flow to supply without pressure, flow at the working pressure, maximum allowable pressure. Diameter recommended by the manufacturer for the suction and discharge, to compare with the actual.
Tank height with respect to the pump (over level or below). Oil level in the tank.
Needless to say, all this information will help you to interpret the test results, to avoid doubts.
By isolating the pump discharge from the rest of the hydraulic system, turn on the motor and let the pump sends the flow through the flowmeter, keeping open the relief valve to the tank. In this way we can meassure the pump flow without any load, which must be equal to that suggested by the manufacturer under no pressure.
Then we start closing the relief valve and we should see how the needle in the pressure gauge rises. When we reach the working pressure, we read the flow and compare it with that suggested by the manufacturer. The difference between the flows with and without pressure gives us an idea of the volumetric efficiency of the pump. Values below 80% are considered low and the pump should be replaced.
Now look at other factors.
If at the time of taking the first flow, the value is less than the one suposed to be with no load, take into account that this may be because the pump is sucking air through the suction or through the shaft seal. From the amount of air that it is sucking will depend how low the flow will be.
Another problem that can make the reading of the flow without pressure is lower is due to a restriction in the suction of the pump, causing an excessive vacuum in the suction generated by the phenomenon known as cavitation. This phenomenon can be confirmed with a vacuum gauge placed at the inlet of the pump as close as possible.
Summary. If the pump does not have problems with the suction, such as aeration or cavitation, the flow readings have 100% certainty about the status of the pump. If we have doubts with the suction, these problems must be solved before measuring the flow at the pump for maximum accuracy.
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