Heat responsive safety device for gate valves

Claim 1

A heat responsive release assembly for an outwardly biased valve stem, the assembly being mounted on a threaded extension of a cylinder for a valve actuator and comprising, an internally threaded sleeve threaded on said extension, an inverted cap detachably mounted within said sleeve, a plug movably mounted within said cap and engaging said stem, a fusible material positioned within the inverted cap between the plug and the adjacent end surface of the inverted cap, said plug being urged by the thrust of the valve stem against the fusible material, said assembly having at least one metering opening for the fusible material provided adjacent the fusible material and upon a predetermined temperature being reached the fusible material melting and flowing through said metering opening to reduce the vOlume of fusible material adjacent said plug to permit outward movement of the plug under the bias of the valve stem, a plurality of spherical ball elements for releasably locking the inverted cap to the sleeve, a plurality of radially spaced openings in the wall of said inner cap receiving the ball elements therein with said ball elements being of a diameter greater than the wall thickness of said inner cap, said sleeve having an inner annular groove therein adjacent said radially spaced openings and receiving a projecting portion of the ball elements for releasably holding the inner cap within said sleeve, said plug having an annular groove therein spaced inwardly of said ball elements when said inner cap is releasably locked in position by said spherical ball elements, said plug groove upon outward movement of said plug being disposed adjacent and receiving said spherical ball elements to permit disengagement of said ball elements from the groove of said sleeve and release of said cap from said sleeve, said cap having a central end opening therein and said plug having a reduced diameter cylindrical extension thereon fitting within said end opening, and said fusible material being ring shaped and fitting about said cylindrical extension between said plug and the end surface of said cap.