Hydraulic motors are suitable for any application requiring mechanical rotational power output, such as screw conveyors, wheel drives, fans, mixers and grinding machines. Their operating principles are as diverse as their applications, ranging from swashplate motors, vane motors and gear motors to the main types of piston motors-curved piston motors, radial piston motors and axial piston motors.
Motors convert hydraulic energy into mechanical rotational energy. Their torque output is a function of both the motor displacement (the theoretical volume of fluid required for one revolution of the motor) and the operating pressure. Furthermore, the horsepower output of a hydraulic motor is a product of torque and speed (typically expressed in revolutions per minute).
Each type of motor excels in certain applications, but may represent a compromise in others. The swashplate motor is the most representative in this series, with designations such as Low Speed High Torque (LSHT), Gerotor, Geroller and Disc Valve. Please note that the latter three are actually different configurations of the same type of motor – yet they share the same basic function, utilising an offset shaft with internal gear structure, equipped with a spool or disc valve.
Cycloidal motors are the least efficient (although every motor has relatively efficient points on its pressure and speed curves), but they perform excellently in low-speed, high-torque applications and offer excellent value for money. They are found in most farm operations, such as conveyors or expanders, as well as in all applications where price is a primary consideration.
Gear motors are very simple, employing the same drive and idler gear layout as gear pumps. Although they are generally no more efficient than cycloidal motors, they are inexpensive and perform well at high speeds. They are most commonly used where such a combination is required, such as for cooling fan drives or pump drives.
Vane motors are the least common of the main types, but they offer respectable performance in terms of efficiency and speed output. They are also available in large displacements, making them ideal for high-torque applications. They utilise a rotor with fixed vanes, much like a vane pump, although some manufacturers employ more complex designs that incorporate vanes on the housing as well. These motors are commonly found in applications such as winches or drilling rigs.
Piston motors are hard to beat in terms of both output and efficiency. Bent-axis piston motors are champions of high-speed operation, capable of withstanding immense pressure and torque at high speeds. Their bent-axis design also makes them highly reliable, able to withstand pressures of 5,000 to 6,000 psi. They are suitable for any application requiring ultra-high speed and ultra-high torque, such as grinding mill or vacuum pump drives. They are not cheap, but their power density is unrivalled.
Radial piston motors are the torque kings of the hydraulic motor realm, boasting not only massive displacement but also exceptional efficiency in generating torque. Whilst they do not match the speed of bent-axis motors, they are the preferred choice for wheel drives or other direct-drive, high-torque applications.
It is worth noting that, whilst no axial piston motor can be described as cheap, they offer unrivalled performance regardless of price.
