Radial piston motors are very efficient and generally have a long life, although the high degree of precision required in their manufacture can raise initial costs.
They provide high torque at relatively low shaft speeds and excellent low speed operation with high efficiency, but do have limited high speed capabilities. Because of the low output speed, in many cases a gearbox is not necessary. Radial piston motors are therefore primarily applied where high torques are required at a low speed, for example: winch drives, concrete mixers, trawlers and plastic injection moulding machines.
Radial piston motor designs are either:
- Crankshaft type – with a single cam and pistons pushing inwards. This type of hydraulic motor has extremely high starting torque characteristics. They are available in displacements from 40cc/rev through to about 12 litres/rev but can sometimes be limited in power output. Crankshaft type radial piston motors are capable of running at “creep” speeds and some can run seamlessly up to 1500 rpm whilst offering virtually constant output torque characteristics. Despite essentially being an old design, this makes them the most versatile type of hydraulic motor.
- Multilobe cam ring type – with a cam ring which has multiple lobes and piston rollers that push outwardly against the cam ring. This produces a very smooth output with high starting torque but they are often limited in the upper speed range. This type of motor is available in a very wide range from about 1 litre/rev to 250 litres/rev. These motors are particularly good on low speed applications and can develop very high power.
Beyond this, specific types of radial piston motor include: compact, dual displacement, fixed displacement, low speed high torque, two speed and variable displacement.