A hydraulic motor is essentially a hydraulic pump in reverse. It has one or more pistons that move in a cylinder, with valves and timing, rather like an internal combustion engine powered by compressed air. Hydraulic Motors are some of the most reliable and powerful actuators available today, and are used in a wide range of domestic and industrial systems and machinery. These designs of actuators work in a different way. http://www.oilmaxhydraulic.com/hydraulic-motors/orbital-motors/