Manual relay valve

Abstract

A three-way normally closed relay valve is provided for selectively effecting a control action in response to pressure of a pilot fluid. A tubular valve body defines a central valve chamber for housing a valve member manually manipulatable into a relay open position for initiating service. A lower piston affixed to the end of the valve member is subjected to pilot fluid pressure, and moves the valve member axially for controlling the flow of fluid between inlet, outlet, and vent ports in the valve body. An orifice in the piston intermittently establishes communication between a pilot pressure inlet port and a chamber within the valve body. The restricted orifice cooperates with a fixed seal to trap pilot pressure above and below the piston as the movable piston passes the fixed seal toward the relay closed position, and thereby prevents the valve member from moving in response to pilot pressure. A subassembly having a threaded connection for sealing engagement with the pilot inlet port is provided for economically adding to or removing from the valve body a relay opening capability in response to a remote fluid pressure and irrespective of pilot fluid pressure. The desired features of a manually responsive, three-way normally closed relay are thus obtained, although the closed relay can be opened without manual intervention by the application of remote fluid pressure.