摘要 |
An impeller arrangement comprises an impeller 10 having at least one first vane surface 26 orientated such that the application of fluid under pressure thereto applies a torque to the impeller 10 in a first rotary direction, at least one second vane surface 28 orientated such that the application of fluid under pressure thereto applies a torque to the impeller 10 in a second, opposite rotary direction, and a valve 34 operable to control the supply of fluid to the first and second vane surfaces 26, 28.
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