A hydraulic machine having: a body having a chamber, an inlet (70, 72) for introducing hydraulic fluid into the chamber, an outlet (66, 68) through which hydraulic fluid leaves the chamber, a rotor rotatably mounted within the chamber, the chamber and the rotor being shaped to define one or more rise regions (61, 63), fall regions (63, 65) and dwell regions (62, 64, 67, 69) between walls of the chamber and the rotor, a shaft extending from the rotor, the rotor having a plurality of slots, a plurality of vanes located such that each slot of the rotor has a vane located therein, each vane being movable between a retracted position and an extended position wherein in the retracted position, the vane is unable to work the hydraulic fluid introduced into the chamber, characterised by vane retaining means (88, 264, 1703, 1704, 300, 348, 384, 600) being selectively actuatable such that, when actuated, the vane retaining means retains the vanes in the retracted position, said vane retaining means being arranged such that pressurized hydraulic fluid actuates the vane retaining means to retain the vanes in the retracted position or pressurized hydraulic fluid deactivates the vane retaining means such that the vanes can move from the retracted position to the extended position,: venting means (250, 232, 414, 608, 700) for venting hydraulic fluid from under the vanes when the vane retaining means are operated to retain the vanes in the retracted position and the vanes each move into and are retained in the retracted position, an under vane passage (102, 221) for selectively receiving pressurized hydraulic fluid to facilitate moving the vanes located in a dwell region from the retracted position to the extended position, and wherein a passage of the venting means communicates with a gallery (102, G, 231) around the shaft when the vane retaining means are operated to retain the vanes in the retracted position, said gallery containing low pressure hydraulic fluid. a body having a chamber, an inlet (70, 72) for introducing hydraulic fluid into the chamber, an outlet (66, 68) through which hydraulic fluid leaves the chamber, a rotor rotatably mounted within the chamber, the chamber and the rotor being shaped to define one or more rise regions (61, 63), fall regions (63, 65) and dwell regions (62, 64, 67, 69) between walls of the chamber and the rotor, a shaft extending from the rotor, the rotor having a plurality of slots, a plurality of vanes located such that each slot of the rotor has a vane located therein, each vane being movable between a retracted position and an extended position wherein in the retracted position, the vane is unable to work the hydraulic fluid introduced into the chamber, characterised by vane retaining means (88, 264, 1703, 1704, 300, 348, 384, 600) being selectively actuatable such that, when actuated, the vane retaining means retains the vanes in the retracted position, said vane retaining means being arranged such that pressurized hydraulic fluid actuates the vane retaining means to retain the vanes in the retracted position or pressurized hydraulic fluid deactivates the vane retaining means such that the vanes can move from the retracted position to the extended position,: venting means (250, 232, 414, 608, 700) for venting hydraulic fluid from under the vanes when the vane retaining means are operated to retain the vanes in the retracted position and the vanes each move into and are retained in the retracted position, an under vane passage (102, 221) for selectively receiving pressurized hydraulic fluid to facilitate moving the vanes located in a dwell region from the retracted position to the extended position, and wherein a passage of the venting means communicates with a gallery (102, G, 231) around the shaft when the vane retaining means are operated to retain the vanes in the retracted position, said gallery containing low pressure hydraulic fluid. venting means (250, 232, 414, 608, 700) for venting hydraulic fluid from under the vanes when the vane retaining means are operated to retain the vanes in the retracted position and the vanes each move into and are retained in the retracted position, an under vane passage (102, 221) for selectively receiving pressurized hydraulic fluid to facilitate moving the vanes located in a dwell region from the retracted position to the extended position, and wherein a passage of the venting means communicates with a gallery (102, G, 231) around the shaft when the vane retaining means are operated to retain the vanes in the retracted position, said gallery containing low pressure hydraulic fluid.