The pressure reducing valve is also divided into two types: direct acting type and pilot type, and commonly used pilot type pressure reducing valve.

Figure 5-15 (a) shows the structural pressure of the pilot pressure relief valve. The first pressure oil P1 enters the oil inlet. The pressure outlet is changed to P2 from the oil outlet, and the P2 is simultaneously through the body 6 lower and end cover 8. to the main valve core 7, and the damping hole 9 on the main valve core is used in the right cavity of the pilot valve 3, and then the cone valve is acted by the damping hole of the cone seat 4.

When the outlet pressure is P2 at the fixed value. The cone valve is closed, and the oil pressure of the upper and the lower ends of the main valve core is equal. The spring 10 makes the main valve core at the bottom end. When the outlet pressure of the valve rises to more than 11 of the pressure regulated by the regulator spring, the poppet valve opens. When the oil is flowing back to the tank through the pilot valve and the oil discharge day, the pressure drop caused by the damping hole is produced. When the pressure difference between the upper and lower chamber of the main valve core is greater than the pre tightening force of the spring 10, the main valve core 7 increases to reduce the gap of the pressure reduction port and increase the liquid resistance, resulting in the drop of the outlet pressure P2.

On the other hand, exports rebounded. Thus, the outlet pressure can be stabilized at the setting value by automatically adjusting the opening of the valve port. The valve mouth of the pump car fittings pressure relief valve is often open type. Because the inlet and outlet ports are connected to the pressure oil, the oil drain port must be separately connected to the oil tank. Adjusting the pressure of the pilot valve spring can adjust the pressure of the pump fitting pressure reducing valve.

If the external disturbance makes the import pressure P1 rise. The export pressure P2 also increased. The main valve core moves upward, the opening of the main valve decreases, the P2 decreases, and the balance is achieved in the new position, while the outlet pressure base wood remains unchanged: vice versa. In this way, the pump fittings pressure relief valve can use the pressure of the outlet pressure and the feedback of force to automatically control the opening of the valve mouth. The pressure of the outlet is basically kept constant, so it is called the fixed pressure relief valve.

When the remote control port K is connected with a remote regulating valve, the setting pressure of the remote regulating valve is lower than that of the pump fitting pressure reducing valve. Two level decompression can be achieved.

Fig. 5-15 (b) is the functional symbol of the pilot-type fixed-value relief valve. Fig. 5-15 (c) Functional symbols of a direct-acting constant pressure relief valve.