Guided vanes hydraulic power system

A hydraulic power system comprising a stator having a central cavity with a wall of non-circular cylindrical shape, and defining two cavity ends, a rotor rotatably mounted in said cavity, a plurality of slots formed in said rotor, said slots being evenly spaced around the periphery of the rotor and said slots extending radially inwards from the periphery of the rotor, a vane located in each of said slots, said vanes being slidable in said slots between outwards and inwards positions, said vanes having an outer edge arranged to be in contact with said wall, guide means being fixed relative to said stator for positively displacing said vanes as said rotor rotates in use, said guide means being arranged to keep said outer surface of said vanes in sliding contact with said wall during said rotation, and at least two fluid passages extending into said cavity through which operating fluid can be introduced into and removed from said cavity, said power system have a selector valve for selectively altering the direction of operating fluid flow through said power system, said selector valve having a valve chamber, a fluid inlet thereto and a fluid outlet therefrom, a pair of ports between said fluid inlet and said fluid outlet in communication with said valve chamber, said fluid ports being connected to one of said fluid passages, and a valve member movable in said valve chamber relative to said fluid inlet and said fluid outlet between first and second positions, where with said valve member in said first position fluid is directed by said valve member from said fluid inlet into one of said ports, and fluid from the other of said ports is directed by said valve member to said fluid outlet, and in said second positions fluid is directed by said valve member in the reverse direction through said ports.