Working:

• It is simplest type valve contains a poppet held in a seat against the spring force as shown in figure .
• It consist of two ports and one of which is connected to the pump and another is connected to the tank.
• The fluid enters from the opposite side of the poppet.
• When the system pressure exceeds the preset value, the poppet lifts and the fluid is escaped through the orifice to the storage tank directly.
• It reduces the system pressure and as the pressure reduces to the set limit again the valve closes.

Different from direct acting type:

Direct-Operated Regulators respond directly to variations in downstream pressure to provide the necessary flow and pressure to satisfy the system set point. Outlet pressure opposes the balance force provided by the spring to determine the plug position. Therefore, for direct-operated regulators, Outlet pressure is also considered the loading force.

Pilot-Operated Regulators consist of the same essential components of direct-operated units (plug and seat, diaphragm, spring) with the addition of a pilot which separates Outlet pressure and the diaphragm loading force .The pilot requires an external sense line connected to the downstream piping. Measuring pressure further downstream of the valves allows for more accurate sensing of the true outlet pressure conditions as it moves the sense point away from the flow turbulence generated by the plug and seat. The pilot valve can simply and effectively be considered a second regulator, providing additional control to the main regulator, improving overall sensitivity and, ultimately, accuracy.