Abstract: 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.