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Causes of Pressure Abnormalities of Hydraulic Power Cylinder

The working pressure of hydraulic power cylinder is one of the most basic parameters of hydraulic system. The normal working pressure will greatly affect the working performance of the hydraulic system. The pressure abnormality of the hydraulic system of the hydraulic power cylinder is often manifested as situations such as the failure of the pressure regulating valve when the pressure is adjusted, the system pressure cannot be established, there is no pressure at all, the high pressure is continuously maintained, the pressure rises and then falls, and the pressure is unstable. Once the hydraulic power cylinder pressure is abnormal, it will be difficult for the actuators of the hydraulic system to perform the normal working cycle. It may appear that they are always in the original position and do not work, the action speed is significantly reduced, and the related control valve group often emits harsh noises during the action, causing the machine to be in an abnormal state, which affects the performance of the whole machine.

1. Reasons for the abnormal pressure of the hydraulic power cylinder

(1) Reasons of hydraulic pumps and high pressure hydraulic motors

① If the hydraulic pump and the high pressure hydraulic motor have been used for too long, the internal wear is serious, the leakage is large, and the volumetric efficiency is low, resulting in insufficient output flow of the hydraulic pump and low system pressure.

(2) The engine speed of the hydraulic power cylinder is too low and the efficiency is insufficient, resulting in insufficient system flow and low hydraulic system pressure.

(3) The position of the directional control device of hydraulic pump of hydraulic power cylinder is wrong or the assembly is incorrect, the pump does not work, and the system has no pressure.

2. The reason of the hydraulic control valve of the hydraulic power cylinder

(1) During the working process, if it is found that the pressure of the hydraulic power cylinder cannot rise or fall, it is likely that the hydraulic cylinder parts like reversing valve has failed, resulting in continuous unloading of the system or continuous high pressure.

(2) Blockage of the orifice of the relief valve of hydraulic power cylinder, burrs on the main valve core, dirt between the valve core and the valve hole and gap, etc., may cause the main valve core to be stuck in the fully open position, and the hydraulic oil output by the hydraulic pump returns directly to the tank through the relief valve, so the pressure oil circuit and the oil return circuit are short-circuited, resulting in no pressure in the system; if the above-mentioned burrs or dirt block the main spool in the closed position, the hydraulic power cylinder system pressure may be very high and cannot be lowered. When the valve element of the overflow valve or the directional valve is stuck, the valve element will not move flexibly, and the executive parts will sometimes move but sometimes stop. When the system pressure is detected, the pressure is unstable.

(3) The hydraulic power cylinder has a one-way valve system. If the direction of the one-way valve is reversed, the system pressure may not rise.

(4) Leakage inside and outside the system, such as serious leakage between the valve core and the valve body hole, will also cause the pressure of the hydraulic power cylinder system to not rise.

3. Other reasons for the hydraulic power cylinder

(1) Too low oil level in the hydraulic oil tank of the hydraulic power cylinder, too thin oil suction pipe, and clogging of the oil suction filter with impurities and dirt, will cause excessive oil suction resistance of the hydraulic pump (when the hydraulic pump is empty, it is often accompanied by harsh noise), resulting in the insufficient system flow and low pressure.

(2) In addition, the oil return pipe of the hydraulic power cylinder is on the liquid surface (the return oil produces foam when it impacts the oil in the tank, causing a large amount of air to be mixed into the oil tank), and the oil suction pipe is not well sealed and leaks, which may easily cause air to be mixed into the hydraulic system and cause the system pressure to be unstable.