Abstract: A hydraulic circuit for operator pre-selection in one exemplary embodiment of the extension of a lift truck upright which utilizes a fixed displacement hydraulic motor operating to adjust either a rotary switch or a potentiometer which is connected to a valve for interrupting the flow to the lift cylinder of the upright at the pre-selected height. The adjusted position of an operator's lift height selector is coordinated with the rotary switch or potentiometer or to effect the selected extension of the upright.

Abstract: A fixed displacement fluid motor or pump of the ball or roller piston type in which a plurality of axially or radially extending reciprocating pistons coact with a cam track to produce output motion or to generate pressure fluid output, respectively. A mechanical locking device, preferably in the form of an expansible retaining ring, is secured to each piston, being adapted to lock the piston in a fixed retracted position and out of contact with the cam in a tapered portion of the cylinder bore in modes of operation during which no motor or pump output is required.

Abstract: A closed recirculating hydrostatic transmission system suitable for driving a traction vehicle. The system includes a pair of hydrostatic engine driven variable displacement pumps either of different displacements or engine driven at different speed ratios and each pump being operative to drive hydrostatic motors at the various wheels and in separate closed loop drive circuits such that accurate flow division as between the circuits is effected for driving the vehicle in four-wheel drive or, at the operator's selection, for driving the motors in the one closed loop circuit at a higher speed in two-wheel drive by means of the pump of larger discharge volume. An operator's control operates both pumps together within the limits of the smaller discharge pump in four-wheel drive, and operates the larger discharge pump within the limits thereof while rendering ineffective the smaller discharge pump in two-wheel drive. Valve means enables smooth transition and shifting between two and four-wheel drive at any time.