in a hydraulic rodless cylinder type actuator , a piston is movable back and forth in a hydraulic cylinder . housing elements are respectively mounted on the opposite ends of the cylinder . parallel output shafts are respectively accommodated in the housing elements and protrude therefrom in a fluid - tight condition . the linear movement of the piston is translated into the rotation of the output shafts by flexible inner power transmission elements . flexible outer power transmission elements are provided on the protruding ends of the output shafts in order to deliver a high output from a high - pressure chamber defined in the cylinder to the outside of the cylinder .