It is a rotary actuator that converts hydraulic energy into mechanical energy. Mechanical power is converted into fluid power--hydraulic power--by a hydraulic pump, which works along with this mechanical device. Using a hydraulic motor 51-series produces force and motion, which allows an external load to be moved. In this motor, a constant supply is provided while the load is driven at a constant speed. The torque of fixed-displacement motor, like hydraulic motor 51 series is constant.