Abstract: This invention resides in a closed system, with permanently fixed end plates, which permits the pump-motor of the present invention to operate either as a combined pump-motor, or as a pump only, or solely as a motor. Rotators of this invention have parallel axes normal to the end plates which they intersect at fixed coordinates. That makes possible direct drive to or from a rotator shaft extension or the enclosing cylindrical rotator.In the device of this invention, the end-plates are non-rotary, but the cylindrical shell or housing always rotates. The plurality of rotators within the cylinder define a plurality of fluid pressure zones. Some of the rotators have a relatively smooth surface; the others have relatively gear-like surfaces. When the unit operates as a pump, a shaft extension of one of the rotators protrudes through one of the end plates and is coupled with an input power source such as the crank or pedals of a bicycle.