The cause of the failure of the hydraulic system

　　In actual work, the failure of the hydraulic machinery actuators is often caused by system pressure loss. There are usually three reasons for system pressure loss:

　　1. Internal leakage of hydraulic components: The hydraulic components are damaged and the leakage is serious, causing the oil circuit to be unloaded and the normal pressure cannot be established. The failure usually manifests itself in the fact that one or some of the mechanisms are difficult to operate, while others operate normally. According to the fault phenomenon, it is judged which hydraulic component has an internal leak, and then it is eliminated in time.

　　2. The relief valve spool cannot be reset: if the hydraulic oil is overloaded, it can be safely protected by the unloading of the relief valve. When the overflow valve spool is operated, if the medium contains impurities (such as damaged rubber seals and residues) or if the opening is too large and too strong and the valve plug is unable to reset, the entire oil system will be unloaded. When this happens, the mechanical actuators often suddenly appear to be inoperable. At this time, the relief valve should be removed for cleaning, and the valve plug should be reset and replaced. After the relief valve is returned to the oil circuit, the opening pressure can be reset by using a load of 1.15 to 1.25 times the mechanical rated load.

　　3. Hydraulic pump failure: If the machine can operate when there is no load (or light load) in a short time, and it can not move when it is heavy, most of the hydraulic pump is abnormal. Check the joints of the bolts or keys in time to see if they are loose. If the hydraulic system has a long time of failure due to pressure drop, it can still work under a certain pressure, which is probably due to insufficient hydraulic pressure of the hydraulic pump itself. When testing the hydraulic pump, it should be noted that since the system pressure needs to be established at the same time as the load and the pressure source, the load should be applied to the oil circuit when judging the oil supply pressure. In the field work, some maintenance workers remove the hydraulic pump outlet pipe or the oil inlet pipe of the actuator, and judge the oil supply pressure of the hydraulic pump according to the oil discharge condition of the hydraulic pump when rotating, which is unreliable. The correct test method is: connect the pressure gauge to the system to remove the fault of the internal unloading of the oil circuit, and then apply appropriate load to the system for oil pressure test. It is also possible to remove the hydraulic pump from the machine, test the hydraulic pump on the test bench, and then troubleshoot. If the hydraulic pump has no repair value, it should be replaced. Special attention should be paid when replacing the hydraulic pump: After replacing the new pump, the medium speed throttle should be tested. Do not immediately increase the engine throttle and use high speed to test the performance of the hydraulic pump. Because the oil pressure is too low or there are many reasons for insufficient oil supply, the failure of the oil circuit or partial unloading may not be completely ruled out. The gap between the components in the new pump is smaller than that of the old pump. Pumps, it is very likely that there will be a "fried pump" accident.