Non-flowing modulating pilot operated relief valve

Claim 1

A pilot operated pressure relief valve system having, in combination, a relief valve having a seat communicating between an inlet and an outlet, a relief valve disc closable on the seat, a dome adapted to cause a pressure therein to apply a closing force to the valve disc, a pilot valve body forming a channel, portions of the channel respectively forming a chamber and an exhaust seat respectively communicating with the inlet and the dome, said body having an exhaust passage communicating with the dome through the exhaust seat, a sleeve movable in the channel and having an exhaust valve disc closable on the exhaust seat and a flow passage extending through an inlet seat and the exhaust valve disc, the flow passage having one end in communication with the chamber and the other end in communication with the dome, a control stem having a first portion forming a wall of the chamber movable axially of the channel in response to pressure changes in the chamber and a second portion forming an inlet valve disc closable on the inlet seat in the direction away from the exhaust seat, and means for applying a predetermined force to the control stem in opposition to the pressure force in the chamber.