Abstract: A selector valve having a valve chamber, first and second ports and a diversion passageway linking two sections of the valve chamber. A valve member is movable such that fluid flow is unchanged to a tank while the flow between three positions, first port, second port and diversion passageway may be infinitely varied.

Abstract: A hydraulic power system comprising a stator (1) having a non-circular cavity with inner wall (2) and a rotor (3) rotatably mounted in the cavity. The rotor (3) has a plurality of radially extending slots formed in its circumference and a vane (18) slidably mounted in each of the slots. Guide means (11) fixed relative to the stator (1) is arranged to guide the vanes (18) in and out of the rotor (3) as the rotor (3) rotates to keep the outer edge of the vanes (18) in sliding contact with the inner wall (2). Additionally, the system discloses a plurality of flow passages in the stator connected via a mode variation valve for series or parallel operation of the system, and a selector valve for changing the direction of operation which may be coupled to a by-pass valve for reducing the output of the system.