Manual pressure relief principle of unloading valve
Turn the handwheel of the unloading valve counterclockwise → unscrew the adjusting screw → the spring force acting on the poppet valve is reduced → the oil acting on the spool valve is enough to open the poppet valve → the oil at the upper part of the spool valve drains to the return oil →The cylinder pressure oil at the lower part of the spool valve is greater than the oil pressure at the upper part of the spool valve→the spool valve is pushed open→the cylinder pressure oil is drained into the return oil→the corresponding valve is quickly closed
Analysis of the abnormality of the unloading valve:
1) The problem of oil leakage outside the unloading valve. Generally, the O-ring seal is damaged, the sealing surface has uneven grooves, or the bolt tightening force is not enough. The damage of the O-ring seal in the above picture can cause leakage. On the other hand, if there is leakage from the split surface of the pilot valve, and there is still leakage after replacing the O-ring and checking the sealing surface, it may be caused by leakage at the O-ring of the spool valve sleeve, and the fitting clearance should be very large. It is small and will not be dismantled for general maintenance unless it is forcibly dismantled for destructiveness.
2) The problem of large internal leakage of the unloading valve. The spool valve is not tightly sealed or the matching gap between the spool valve and the sleeve is too small, which causes the spool valve to jam and not close properly.
3) After the steam turbine is turned off, the valve closes slowly. After the newly purchased unloading valve is installed, the unit turns off and the valve closes slowly. It is necessary to check whether the corresponding orifice is blocked, or some manufacturers add plugs to the oil hole for emergency interruption when supplying, resulting in interruption of oil leakage. If it does not go, it will cause the valve to close slowly. Another aspect is to analyze the problem from the outside of the entire EH oil system. A high-profile door crisis occurred in a factory to interrupt the blockage of the oil pipe, resulting in the problem that the high-profile door closes slowly after the unit is turned off.
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