Farris 3800 series pilot operated pressure relief valve

In a pilot operated valve the process pressure itself holds the main valve closed: it is piped through the pilot into the dome above the piston, so seat load increases as the pressure rises. The valve therefore stays tight up to a few percent below set pressure and is unaffected by back pressure, which makes the 3800 the choice where a spring valve would simmer or where the header pressure varies.

Snap-acting pilots open the main valve fully at set pressure, for gas and vapour with adjustable blowdown. Modulating pilots open the valve only as far as needed, which limits product loss and reaction forces and suits liquid and steam service. All pilots are non-flowing, so no process fluid passes through the pilot in the closed position.

The main valve has an integrally cast flanged body with semi-nozzle, standard in carbon steel with 316 stainless trim; a full port version gives the highest capacity per size.

Selection data we need

Medium and state, set pressure, required capacity or the governing relief scenario, operating pressure and temperature, back pressure, inlet and outlet size and rating, material and certificates. For a replacement, the nameplate data is enough. We size and select in Farris SizeMaster.