Plug valve actuator

In a plug-type valve having a body with a plug chamber and diametrically opposed inlet and outlet ports communicating with said chamber, a plug in said chamber having a transverse passage therethrough and an upstanding stem, said plug being shiftable between a first, upper, valve-open position with its transverse passage in alignment with said inlet and outlet ports and a second, lower, valve-closed position wherein the axis of said transverse plug passage is oriented at 90.degree. to the axes of said inlet and outlet ports, seal means on said plug, said seal means being in engagement with the interior surface of said chamber about said inlet and outlet ports when said plug is in said second, valve closed position, a bonnet closing the upper end of said chamber, a packing gland mounted in said bonnet through which said plug stem extends, the improvement comprising a yoke having a vertical axial bore therethrough, said yoke having a lower end affixed to said bonnet with the stem of said plug extending into said axial bore of said yoke, said yoke having an upper end, a bearing cap mounted on said upper end of said yoke, a drive nut having a vertical, threaded, axial bore, said drive nut being rotatively mounted in said bearing cap, a valve stem, the upper portion of said valve stem being threaded and being engaged in said threaded axial bore of said drive nut, said valve stem and said plug stem being coaxial, a single cylindrical coupling located within said axial bore of said yoke and being both rotatable and shiftable vertically therein, the lower end of said valve stem and the upper end of said plug stem both being non-rotatively affixed to said coupling, one of said yoke and said coupling having a single pair of diametrically opposed identical cam slots formed therein, a cam follower for each of said cam slots being supported by the other of said yoke and said coupling, said cam slots being so configured that when said cam slots are located in said yoke they are in an inverted position from that which they occupy when located in said coupling, such that upon turning said drive nut in one direction, said plug in said valve-open position will be simultaneously partially lowered and turned 90.degree. and thereafter lowered without rotation to said valve-closed position with said plug seals in engagement with said chamber interior surface about said inlet and outlet ports, and upon turning said drive nut in the opposite direction, said plug will first be lifted vertically without rotation out of sealing relationship with said chamber inlet and outlet ports and thereafter will be simultaneously lifted and rotated 90.degree. to said valve-open position, whereby to provide a structure which is simple in construction, compact and self-locking.