Abstract: A rotary machine usable as a pump, compressor, turbine or motor, for example. Rotating piston cylinders have radially movable pistons therein and the cylinders are mounted within a control ring and a housing. The control ring is tangentially pivoted within the housing to vary the volume flow through the machine and the torque application transmitted by a shaft, as well as the direction of flow through the machine. Pressure fluid operated balancing pistons are used to counter the axial thrust placed on the rotor by liquids applied to the rotor, regardless of the direction of flow through the machine.