Abstract: A motor driven by pressure medium supplied from an external pressure source. The motor comprises a motor casing with a working chamber, a stator pail which forms an axial supply pipe for supply of pressure medium to the working chamber, a rotor part which is rotatably mounted on the stator part and eccentrically arranged in the working chamber, the rotor part and the stator being provided with inlet ports for supply of pressure medium to the working chamber, a hinge part mounted on the rotor part and provided with a pivotably mounted piston which divides the working chamber into a pressure chamber and a discharge chamber, and a constantly open discharge opening which is arranged in the wall of the motor easing from the discharge chamber through which the medium is discharged.