Working principle: According to the working principle and structure, pressure reducing valve is divided into direct acting and pilot type two categories.
1. Function and performance requirements: pressure reducing valve is used to reduce the pressure of a circuit in the system. Make the outlet pressure is reduced and constant pressure reducing valve called fixed output pressure reducing valve; The difference between the outlet pressure and a certain load pressure is constant pressure reducing valve called constant difference pressure reducing valve; Make the inlet pressure and outlet pressure ratio of a certain reducing valve called constant ratio reducing valve. The requirement for a constant output reducing valve is that the outlet pressure should remain constant regardless of the inlet pressure and not be affected by changes in the flow through the valve. For a constant difference or constant ratio reducing valve, the pressure difference or their ratio should be constant regardless of how the inlet pressure or outlet pressure changes.
2. Performance of the pressure reducing valve: In addition to similar characteristics with the relief valve, the following performance is also required:
a. Outlet pressure changes caused by inlet pressure changes should be small. Generally, the greater the pressure difference between inlet and outlet, the more stable the outlet pressure is when the inlet pressure changes.
b. The change of outlet pressure caused by the change of flow through the valve should be small;
c. For one-way pressure reducing valves, small reverse pressure loss is also required.
3. Selection of reducing valve: when choosing reducing valve, the change trend of opening and closing characteristics of reducing valve should be considered in contrast to the relief valve, that is, the secondary pressure is reduced when the flow of reducing valve is increased. Attention must be paid to the relationship between the setting pressure of the reducing valve and the working pressure of the actuator. Pilot pressure reducing valve discharge more than other control valves. There is always oil flowing from the pilot valve, may be as much as 1L/min above, affecting the choice of pump capacity. The adjustment range of secondary pressure depends on the spring used and the flow through the valve. The minimum regulating pressure should ensure that the difference between primary pressure and secondary pressure is 0.3 ~ 1MPa. When the flow rate through the valve is much less than the rated flow rate, it is easy to produce vibration or other unstable phenomena. At this point, take action on the circuit.
