Unit-testing query transformation rules

A manual override drive apparatus for use with normally powered driving assemblies, such as valve actuators, is disclosed which has a body having an axial bore therethrough, a shaft movable axially but not rotatably extending through the bore and having screw threads thereon, a cage in the body rotatably disposed about the shaft having elongate circumferentially arranged pockets and restrained against axial movement by thrust bearings, a plurality of elongated gear segments movably disposed in the pockets having screw threads which mate with the threads on the shaft, cam means operable to move the gear segments toward and away from the shaft for engagement and disengagement of the screw threads on the shaft and the gear segments, and means operable to rotate the cage and thus the gear segments thereby driving the shaft axially when the gear segments are in threaded engagement with the shaft.