When a hydraulic excavator was used for 600H and 1800h, there were two failures: the right track was unable to walk and the bucket was unable to dig. After inspection, it is found that the two failures are related to the damage of P2 pump regulator.
The main pump of the excavator is composed of two variable piston pumps (P1 and P2 pumps). After the failure of the regulator of P2 pump, the flow regulation of the pump failed. A new regulator assembly was replaced in both repairs, and then the excavator returned to normal.
After disassembling the damaged regulator, it is found that the negative feedback pilot piston is broken. After the pilot piston was broken, the flow of P2 pump could not be adjusted, resulting in the above failure of the excavator. The analysis shows that the fracture failure of the pilot piston of the regulator rarely occurs in other excavators. If the cause of the fracture of the pilot piston cannot be found, just replace the regulator, and such failure will occur in the future.
After disassembling the fault regulator, we found that the fracture position of the pilot piston is just the position where the pilot piston is connected with the drive connecting rod II, which is the weakest area of the whole pilot piston. The fracture may be due to the problem of its material or too high oil pressure.
This type of main pump has been equipped with a large number of excavators and has been used for a long time. There has been no similar fault before. Therefore, it is necessary to analyze the cause of the fault from the pilot control oil circuit to eliminate the possibility of fracture caused by defects in the design of the pilot piston and problems in materials.
P2 pump regulator pilot piston pressure comes from the main control valve PS2 negative feedback oil circuit. Since the main oil channel is equipped with a protective overflow valve, and its overflow pressure is set to 3.8mpa, the negative feedback pressure generally will not exceed this pressure value. Suppose that after the failure of the main overflow valve, the high-pressure oil circuit will enter the negative feedback oil passage, which can cause an abnormal increase in pressure and lead to the fracture of the pilot piston.
The reason for the abnormal rise of negative feedback pressure is that the overflow valve does not play an overflow role, and the reason is that the overflow valve is stuck inside. After replacing the new relief valve, test the negative feedback pressure again, which is within the normal range of 0 ~ 3Mpa. After maintenance, the excavator has been used for 4000H, and there is no fracture of P2 pump regulator pilot piston.
The main pump regulator is stuck, which will cause abnormal action of the excavator. It is generally considered that it is caused by pollution of the hydraulic system or wear of the regulator itself. Replace the regulator and replace the hydraulic oil. During the first maintenance of the machine, the failure occurred again because there was no in-depth analysis of the failure. When it happened again, we paid full attention to it and carried out careful analysis and test, so as to find out the real cause of the fault.
