Drive apparatus for a rotary spindle valve having an elongated screw and a feed nut located on the screw connected by lever means to the rotary spindle. The feed nut is slidably maintained between a pair of rails having planar surfaces engaging opposite faces of the feed nut. One of the rails is adjustably mounted to enable the planar surfaces to be maintained parallel to each other. Low friction slide plates are removably provided on the feed nut.
