Valve actuator

Claim 1

An actuator for actuating a valve having a reciprocating elongate operating stem comprising: a housing; a piston slidably disposed in said housing and operable by fluid pressure on one side of said piston to move the piston toward a first end of said housing, said piston being connected to said valve stem through a cylindrical extension of said piston which is in sliding and sealing engagement with a passageway through one end of said housing; a spring biasing said piston toward a second end of said housing; and a ball bearing mechanism comprising a nut member attached to said piston and a screw member rotatably mounted on bearings at one end of said housing, said nut member being threadedly engaged with said screw member through ball bearings carried by said nut for circulation from one end of said nut to the other, one end of said screw member projecting through an aperture in said housing and adapted for engagement with manual operating means for rotation of said screw to reciprocate said nut member and said piston within said housing; and including guide rods longitudinally disposed in said housing and in sliding engagement with said piston through apertures therein, said one side of said piston being pressure isolated by seals around said piston, around said rods and around said extension.