Testing of Lubrication Systems

The hydrostatic testing is the first test used on the lube system. The system is tested while assembled or partially assembled, based on the particular system. A test pressure of VA times the maximum allowable working pressure, a minimum of 20 psi for the oil side, is used for the test. For the oil-wetted parts, the test fluid should be light oil, which is normally the recommended lubricant for the compressor train. The test period is the length of time needed to inspect for leaks, or a minimum of thirty minutes. Acceptance is based on the lack of leaks as visually observed or the lack of a drop in the test pressure.

The operational test of the lube system is, as the name implies, a functional test to check as many of the features as practical under running conditions. The first and last step is a demonstration of the cleanliness of the system. This is followed by a running test of a four-hour duration. The test should simulate the field operation with the compressor in every way practical. All equipment to be furnished with the lube system should be used in the test, including the standby pump start and trip switches. All other instruments should be used to demonstrate their operation. Prior to starting the four-hour run, the system should be thoroughly inspected for leaks and the leaks corrected. If no steam is available for a steam turbine (if one is used), the four-hour run can be made on the electric pump. However, every effort should be made to use an alternate source of energy such as compressed air, to operate the steam turbine.

For the standby pump start test, which is an important test to ensure the pumps transfer without large pressure swings, a check should be made to see if the relief valves lift or the pressure falls to a pressure one half the difference between the standby pump start pressure and the compressor trip pressure. The transient pressure is best measured with a multipen chart recorder. The chart speed must be high enough to fully display the pressure variation. While not as good as the chart recorder, a simple shopmade test setup can be substituted. A spare switch is temporarily connected to the same location as the other switches. This switch is calibrated to close at the threshold acceptance pressure. The contacts are wired to a test light through a seal relay. The purpose of the relay is to maintain the cir-

cult when the pressure restores, so the light will remain on if the switch reached its setting. On the transfer, if the test light is illuminated, the con sole failed the test. Obviously, this test must be made with both pumps operational. The same is true for control valve response, though the bal ance of the control valve operation can be done with the standby pump. Because of the problems involved in simulating events, it is best to conduct the test with the main pump if at all possible. As many as practical of the operational steps should be performed. The transfer valves for the coolers and filters should be operated. The pressure should not fall to the standby pump start level in the transfer, if control oil is being supplied, a governor transient should be simulated to check the pressure level for a drop to the level of starting the standby pump. A check should be made of the transfer valves to demonstrate that the leakage is less than the filter body draining capacity. A zero leakage is preferred.

The lube system is considered acceptable when no abnormal conditions occur during the test. Instability or excessive pressure swings during one of the steps is considered an abnormal condition. Corrections to the system will be required and the system retested and demonstrated to be free of the abnormalities before it can be considered acceptable.

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