A valve assembly of the type wherein a valve stem operatively connected to a valve closure element is longitudinally moved between open and closed valve positions comprises a longitudinally movable nonrotatable valve stem in threaded engagement with an axially fixed bushing rotatably mounted on said body so that rotation of the bushing in opposite directions effects opposite longitudinal movements of said valve stem. A reservoir of lubricant under pressure is disposed within the stem with passage means extending between said reservoir and an engagement surface zone of the threads. A transverse cylinder on the stem responsive to longitudinal movement of said valve stem in either direction is actuated for automatically feeding lubricant along the passage means from said reservoir toward said zone.