A rotary fluid energy translating device which comprises a casing and a couple ring rotatably supported in the casing. Static fluid pressure is applied to the couple ring at circumferentially spaced points and from both the outer and the inner side of the ring so that a couple of forces is produced in the couple ring while providing balanced static pressure on the ring at each of the circumferentially spaced points thereby to rotate the couple ring, which can be connected to a mechanical element outside the casing. By positively rotating the couple ring by means of an external drive, it is possible to operate the device as a fluid pump.