Hydraulic Motor
A hydraulic motor is the actuator that converts incoming flow rate into continuous rotary motion. Its speed is set by flow rate and its torque by pressure difference: giving 40 l/min to a 200 cm3/rev motor gives a theoretical speed of 200 rpm. It is used in crane drums, tracked travel drives, and slewing table drives.
It is the rotary counterpart of the cylinder. Speed is calculated by dividing flow rate by displacement, and torque is found from the product of pressure difference and displacement. On a 200 cm3/rev motor a 150 bar pressure difference produces about 480 Nm of torque; because of volumetric and mechanical efficiency the actual value is below that.
- Orbital (gerotor) type: low speed, high torque; common in agriculture and mobile equipment.
- Piston type: high pressure and efficiency, with a variable displacement option.
- Drain line: on most motors the case drain must return directly to tank and unpressurized; if this line is restricted, the seal blows.
On a hydraulic motor controlled by a manual lever, speed varies proportionally with how far the lever is opened. When electronic lever control is added, this stepless control is preserved remotely as well; what determines speed is still the flow rate passing through the valve, and the remote control only manages the position of the lever.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle