Heat responsive safety device for gate valves

Claim 1

A fire safety valve structure comprising a valve body, a gate valve movable between open and closed positions in said body, a cylindrical housing on the valve body having a piston member mounted therein, a stem connected to said piston member and the gate valve and movable therewith, said cylindrical housing having an axially extending central opening, said stem having an outer end portion extending within the central opening, means continuously biasing the piston member and stem toward the closed position of the valve, and heat responsive stem release means on said housing adjacent said central opening to maintain the valve in its open position, said stem release means including at least two fusible material chambers each having a fusible material confined therein, a piston mounted within each chamber for movement in a direction generally transversely of the longitudinal axis of the stem upon melting of the fusible material and engaging the fusible material across substantially the entire surface of the fusible material adjacent the piston, the pistons holding the stem in an open position of the valve and being continuously urged by said stem against the fusible material in said chambers to place the fusible material under a substantially wholly compressive loading, and a metering opening of a restricted size communicating with each chamber, the wall surfaces defining said chambers being in contact with the entire adjacent surface of the fusible material except the portion of the fusible material exposed to the metering openings, said fusible material upon reaching a predetermined high temperature melting across substantially its entire cross section and being forced into said metering openings from the compressive forces exerted by the pistons against the confined fusible material thereby to permit a simultaneous movement of the pistons to release the stem for movement of the gate valve to a closed position.