Handling of abnormal hydraulic system pressure

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According to Engineer Li, a senior consultant at Hydraulics Talent Network under Yilan, low and high pressure in hydraulic systems are typical faults of such systems. If the hydraulic pump, control valves, or actuator components fail, it will cause abnormal pressure in the hydraulic system. 1. Low pressure a. No pressure at all. This indicates that the power components in the system are not supplying pressurized oil; it is necessary to check all the components between the hydraulic pump and the oil tank. First, check whether there is enough hydraulic fluid in the tank, and whether the filter and oil pipes are clogged. Then, disconnect the outlet connector of the hydraulic pump to see if hydraulic fluid can be discharged. If there is no oil output, it is due to a problem with the installation or connection of the hydraulic pump; it may be that the pump is oriented incorrectly or the inlet and outlet ports are reversed. b. Pressure is below normal levels. Dr. Zhang from Hydraulic Talent Network believes that in such cases, the relief valve should be checked, and the readings on the pressure gauge should be monitored in order to identify the source of the problem. If the pressure does not change when adjusting the relief valve, the fault lies with the relief valve. The reason may be: poor sealing between the spool and the valve seat of the relief valve ； The seal between the valve seat and the seat hole is damaged ； Fatigue fracture of pressure regulating spring ； The spool or its auxiliary ball valve (or cone valve) is stuck in the open position. If the damping holes on the main spool become blocked, hydraulic oil cannot reach the upper chamber of the main valve and the front chamber of the pilot valve; as a result, the pilot valve loses its ability to regulate the pressure of the main valve, causing it to function as a direct-acting relief valve. At this point, the main spool opens for overflow, and the system is unable to build pressure. If the flow rate output by the hydraulic pump decreases significantly and the pressure does not reach the rated value, there may be a fault with the hydraulic pump. At this time, it is necessary to check whether the components inside the pump are damaged or stuck, whether the seals and bearings are damaged, and whether all the joints are properly sealed. If the clearance between the components inside the hydraulic pump exceeds the technical specifications, it can also cause pressure fluctuations and a drop in pressure. Even in new hydraulic pumps, there are sometimes casting shrinkages or sand holes in the pump body, which allow the suction chamber and the pressure chamber to communicate with each other, resulting in the pump’s output pressure not reaching the required operating level. Furthermore, issues such as control valves in the pressure oil lines becoming stuck due to dirt buildup, severe leakage in those control valves, loose pipe fittings, or internal leaks in the hydraulic cylinders can all cause the oil pressure to drop below normal levels. 2. Excessive pressure: Engineer Li from Shanghai Hydraulic on the Hydraulic Talent Network believes that the main cause might be a fault in the pilot relief valve. When the damping hole on the pilot valve seat becomes blocked, the pressure oil cannot push the pilot valve open to allow oil to flow out, and no oil flows inside the valve. At this point, the pressures in the upper and lower oil chambers of the main spool are equal; the pilot valve loses its ability to regulate the pressure of the main spool. Under the force of the spring, the main spool remains in a closed position, preventing any overflow. The pressure before the relief valve increases as the load increases. When the hydraulic cylinder or motor reaches its end position, the external load increases indefinitely, and the system pressure reaches its maximum value. Furthermore, damaged seals inside the relief valve, as well as excessive wear of the main spool and cone spool, can cause abnormal system pressure ； Spring deformation or being too soft can also cause unstable adjustment pressure.