Low pressure and high pressure are typical faults of hydraulic system. Hydraulic pump, control valve and actuating element if have breakdown, can cause the pressure of hydraulic system to appear unusual.
1. pressure is too low (1), there is no pressure at all. This means that the power element in the system does not provide any pressure oil, and all components between the hydraulic pump and the tank should be checked. First, check that the tank is full of hydraulic oil, the oil filter and the oil pipe are blocked, and then take the hydraulic pump out of the oil outlet to see if it can output hydraulic oil. If there is no oil output, it is the hydraulic pump installation or connection failure, may be the hydraulic pump turn wrong, or the inlet and outlet connected to the reverse.
(2) the pressure is lower than the normal value, at this time should check the overflow valve, observe the pressure gauge reading changes, determine the fault point. If the relief valve is adjusted, the pressure is not changed, indicating that the fault is in the relief valve. The reason may be: the overflow valve spool and valve seat seal is not good; seat and seat hole seal damage; pressure spring fatigue fracture; spool or its auxiliary ball valve (or cone valve) stuck in the opening position.
if the main valve spool of the damping hole plug, hydraulic oil can not be transferred to the main valve cavity and pilot valve in front of the cavity, the pilot valve will lose the main valve pressure regulating role, so that the main valve to become a direct acting relief valve. At this point, the main valve open overflow, the system will not establish pressure.
if the output flow of the hydraulic pump is reduced significantly and the pressure is not up to the rated value, the hydraulic pump may be out of order. At this point, should check the pump parts are damaged, stuck, seals and bearings are damaged, the joint surface is sealed.
if the clearance between the parts in the hydraulic pump exceeds the technical specifications, the pressure pulsation will also cause the pressure to drop. Even if the new hydraulic pump sometimes existing pump casting shrinkage or sand hole, the oil suction chamber and the pressure chamber to cause oil pump pressure is not up to the pressure of work.
in addition, the pressure in the oil pipe road control valve due to dirt blockage and other reasons, hysteresis, the control valve has serious leakage or loose pipe joints and hydraulic cylinder leakage, etc., will cause oil pressure below normal.
2. pressure is too high, the main reason is that the pilot relief valve failure. When the damping hole on the pilot valve seat is blocked, the pressure oil can not push the pilot valve to open the oil drain, and no oil flow in the valve. Under equal pressure oil cavity at the main spool, the pilot valve out of the main valve pressure regulation, under the action of the spring force the main valve is closed, can not overflow, the overflow valve before the valve pressure increases as the load increased, when the hydraulic cylinder or hydraulic motor movement to the end point, the external load infinite increasing system pressure reaches the highest. In addition, the overflow valve seals damaged, and the main spool and cone valve wear too much, will cause abnormal system pressure; spring deformation or too soft, will also make the adjustment pressure instability.