Patent attributes
Hermetic gate valves and globe valves having a bonnet assembly that does not require stem packing and includes a harmonic drive and locking mechanism. The bonnet assembly includes a main body which is sealingly engaged on the valve body and includes an elongate tubular portion that completely encloses the valve stem and has a sidewall with an internally threaded portion formed of a material so as to be relatively flexible radially inward toward the valve stem, and is surrounded by an outer sleeve having a sidewall formed of a material so as to be relatively rigid radially and defining an annulus therebetween. A roller assembly rotatably disposed in the annulus includes pairs of diametrically opposed rollers including a pair of wave generator rollers positioned to rotatably engage the exterior of the tubular portion and press it radially inward to assume an elliptical configuration such that the threads of the tubular portion are engaged with the exterior threads of the valve stem at two diametrically opposed locations, with intermediate diametrically opposed locations of non-engagement. A removable handwheel keyed to the roller assembly rotates the rollers such that the engaged threads at two diametrically opposed circumferentially spaced locations, with intermediate diametrically opposed locations of non-engagement causes relative motion axially to convert the rotary motion to linear motion thereby driving the valve stem and the valve element at the bottom end thereof longitudinally between the open and closed positions.
