The working principle of the quick unloading valve is connected with a cup slide valve at the upper part, the lower chamber of the slide valve communicates with the high pressure oil line at the lower part of the oil pump piston, and is subjected to high pressure oil, in the middle of the bottom of the cup slide valve. There is a small hole, which allows a small amount of pressure oil to pass through the upper oil chamber of the slide valve. There are two ways in the oil chamber. All the way through the check valve is connected to the critical oil circuit. During normal operation, the oil pressure on the main oil is equal to the high pressure. The hydraulic pressure of the oil presses against the check valve and closes it. The pressure oil in the upper part of the slide valve cannot escape from this way. The other oil flow path is through the shrinkage hole controlled by the needle valve, and the control leads to the upper cavity of the oil pump piston. The passage of the oil and adjustment of the opening of the needle valve can adjust the oil pressure on the slide valve for debugging and setting purposes. In the normal operation, the hydraulic force on the upper part of the spool valve plus the force of the spring is greater than the force of the high refueling on the lower part of the spool valve, so that the cup-mounted spool valve is pressed on the base, the oil port connected to the return oil is closed, and the turbine is faulty The solenoid valve acts to interrupt the pressure loss of the main oil pipe. The pressure oil acting on the cup-shaped spool valve opens the check valve and drains the oil. The oil pressure in the upper part of the valve drastically decreases, and the lower high-pressure oil pushes the slide valve upward. The drain port on the upper part of the valve sleeve is opened, so that the high-pressure oil in the oil pump is depressurized, and under the action of the spring force, it rapidly drops and closes the main valve to stop the unit.