Fail-safe actuator

Claim 1

A fail-safe actuator for moving a rotary stem of a plug-type service valve, to dispose the plug to operative and inoperative positions, and comprising in combination: a fluid motor including a housing having a chamber presenting an arcuate inner wall surface, and an oscillatable vane having equal opposed areas movable within the chamber and against said wall surface between one limit of travel near one end of the arcuate inner wall surface and a second limit of travel near the other end of the arcuate inner wall surface; a rockable rotary shaft supported by said housing and connected with said vane for movement with said vane, said shaft coupled to said valve stem for corresponding movement of said stem with said shaft; a first port in fluid communicative relationship with the housing chamber at one end thereof on one side of the vane; a second port in fluid communicative relationship with the housing chamber on the other side of the vane, a first conduit connected with said first port and with a source of fluid pressure, a control valve controlling a flow of pressurized fluid from said fluid source to said first port of the chamber, for driving the vane from its said one limit of travel to its second limit of travel; an external storage tank for pressurized fluid, an external bypass conduit connected with said storage tank and in communication with said first port; a restricted flow orifice in said bypass conduit including a means for adjusting said restricted orifice for bypassing into the storage tank a portion of the pressurized fluid supplied to said first port through the control valve, said orifice providing for two-way movement of fluid therethrough at a limited flow rate, and an external second conduit connected with said storage tank and with said second port and in open, free communication therewith to supply fluid pressure from said storage tank to said chamber to return the vane to its said one limit of travel upon occurrence of failure of fluid pressure at said first port, said restricted bypass conduit, said storage tank, and said first and second conduits resulting in equalization of fluid pressure on opposite sides of said piston at its respective limits of travel.