The maximum performance of hydraulic motors in term of pressure, flow, torque output, speed, efficiency, life and physical configuration is determined by:
- Pressure capability of internal and external components
- Internal leakage characteristics
- Efficiency of force and power transmission
Hydraulic motors are rated according to displacement, torque capability, speed and maximum pressure limitations.
Displacement is the amount of fluid required to turn the motor output shaft one revolution. Motor displacement is expressed in cubic inches per revolution. Displacement of hydraulic motors can be fixed or variable. With input flow and operating pressure constant, the fixed displacement motor provides constant torque and constant speed. Under the same condition, variable displacement motor provides variable torque and variable speed.
Torque is the rotational force component of the motor’s output. It is turning or twisting effort by the output shaft. Torque output of a motor is expressed in pound inches or pound feet and is a function of system pressure and motor displacement. Motor torque figures are usually given for a specific pressure differential or pressure drop across the motor. Theoretical figures indicate the torque available at the motor shat if the motor operated at 100 percent efficiency.
Motor speed is a function of motor displacement and the volume of fluid delivered to the motor.
Pressure required in a hydraulic motor depends on the torque load and the displacement. A large displacement motor will develop a given torque with less pressure than a smaller unit. Motor will have a maximum pressure rating, which is the highest inlet pressure the motor can continuously withstand for an adequate period of time without damage.