When the output pressure of the pressure reducing valve is high or the diameter is large, the pressure is directly adjusted by the pressure regulating spring, the spring stiffness is inevitably too large, and when the flow rate changes, the output pressure fluctuates greatly, and the structural size of the valve also increases. In order to overcome these disadvantages, a pilot operated pressure reducing valve can be employed. The working principle of the pilot type pressure reducing valve is basically the same as that of the direct acting type. The pressure regulating gas used in the pilot type pressure reducing valve is supplied by a small direct acting pressure reducing valve.
If the small direct acting pressure reducing valve is installed inside the valve body, it is called the internal pilot type pressure reducing valve; if the small direct acting pressure reducing valve is installed outside the main valve body, it is called the external pilot type pressure reducing valve. . Compared with the direct-acting pressure reducing valve, the valve adds a nozzle baffle enlargement consisting of a nozzle, a baffle, a fixed orifice and a gas chamber.
When the distance between the nozzle and the baffle changes slightly, the pressure in the chamber changes significantly, causing a large displacement of the diaphragm to control the up and down movement of the spool to make the intake port Open or close small, improve the sensitivity of the spool control, that is, improve the voltage regulation accuracy.
The main valve of the external pilot type pressure reducing valve works in the same way as the direct acting type. There is also a small direct acting pressure reducing valve outside the main valve body to control the main valve. This type of valve is suitable for applications with a diameter of 20mm or more, a long distance (within 30m), a high point, a dangerous place, and difficulty in voltage regulation.