Pilot operated relief valve - has two=stage pilot valve with testing facility in operating communication with main relief valve

摘要

The pilot operated relief valve includes first and second pilot stages (10, 41) and a balanced amin relief valve. A valve body contains the stages and includes two inlet (11, 12) exhaust (13) and test (14) ports. A first stage poppet (18) co-acts with a first seat below stage plunger (48) has upper product pressure. A second stage plunger (48) has upper and lower ends and co-acts with second and third seats for first and second plunger positions. - The first seat and inlet port (11) are in communication as the first seat and upper plunger end, and the inlet port (11) and second seat for a first plunger position. Inlet port (12), exhaust port (13) and the third seat are in communication for a second plunger position. Product pressure, exceeding the predetermined value, moves the poppet (18) from the first to the second position and the plunger moves to the second position thereby isolating inlet port (11) to prevent further product flow through the first seat. Flow is then initiated through inlet (12) and exhaust (13) to operate the main valve.