Troubleshooting methods for abnormal noise from the main pump of the excavator

After a PC200-6 fully hydraulic excavator was started, the working device could perform various actions, but the main pump emitted abnormal noise.

Preliminary analysis suggests that it is caused by either the pump being sucked in or air being mixed into the oil circuit. Therefore, first adjust the working device to the oil level detection position. After inspection, it was found that the oil level in the hydraulic oil tank was below the low position indicated by the oil gauge, which was a position of oil shortage. Upon inquiry with the driver, it was learned that the sealing ring of the high-pressure oil pipe leading to the rodless cavity of the boom cylinder had been replaced due to oil leakage during operation, but the oil level was not checked in time after the replacement. So, first, the hydraulic oil tank was filled with oil to the standard level. The test run showed that although the abnormal noise had decreased somewhat, it still existed. Then, after venting the main pump through the main pump exhaust valve and re-testing the machine, it was found that the abnormal noise still existed, indicating that this noise could not be completely caused by the pump's suction.

Next, both the suction oil filter element and the return oil filter element of the hydraulic oil tank were inspected. It was found that the suction oil filter element had turned black and had oil sludge, while the return oil filter element was adhered with brown metal particles. Therefore, the above-mentioned filter elements were replaced. Considering that there were brown metal particles adhering to the return oil filter element, the oil from the main pump was drained and inspected, and it was found that there were also brown metal particles. At the same time, when disassembling and inspecting the main pump, it was found that there was no damage to the piston, distribution plate, swash plate, etc., but the sliding shoes were worn. After replacing it, the assembly was carried out strictly in accordance with the requirements. The hydraulic system was cleaned and the oil was changed. When the test machine was started again, the abnormal noise disappeared and the fault had been eliminated.

Under normal circumstances, the possible causes of abnormal noise around the main pump are as follows:

Insufficient hydraulic oil causes the main pump to be sucked empty. Air has mixed into the oil suction pipeline. The clogging of the oil suction filter element causes the main pump to be sucked empty. Internal wear of the main pump causes abnormal noise during its operation.

In this example, the abnormal noise is caused by insufficient hydraulic oil and wear of the sliding shoes inside the main pump. The reason is that after replacing the sealing parts, the oil level was not checked in time, resulting in insufficient hydraulic oil and causing the main pump to have an empty suction phenomenon. When the oil mixed with air flows through the main pump, the sliding shoes fail to float up or float insufficiently at certain moments, resulting in the inability to form a good lubricating oil film between the sliding shoes and the swash plate, causing the sliding shoes to wear out and eventually leading to abnormal noise during the operation of the main pump.