The ultimate guide to hydraulic motors

The ultimate guide to Hydraulic Motors

There are many different types of hydraulic motor. Most of them can be categorised as: axial piston motors, radial piston motors, hydraulic Gear Motors or hydraulic vane motors.

Unlike a linear, force-moving cylinder, the hydraulic motor uses hydraulic pressure to rotate. A hydraulic motor is built very much like a pump. However, when operated, oil enters the hydraulic motor and turns the shaft. The amount of oil supplied by the hydraulic pump determines the speed of a hydraulic motor. Subsequently, the torque is dependent on the amount of pressure supplied.

Learn about radial piston motors

Radial piston motors are highly efficient and generally have a long life. Furthermore, they provide high torque at relatively low shaft speeds, as well as excellent low speed operation with high efficiency. The low output speed means that, in many cases, a gearbox is not necessary.

Radial piston motors are often referred to as LSHT – Low Speed High Torque motors. We supply radial piston motors from brands worldwide, including Bosch Rexroth, Staffa (Kawasaki) and the Italgroup.

Which applications are radial piston motors commonly found in?

Radial piston motors are commonly fund in: excavators, cranes, ground drilling equipment, winch drives, concrete mixers, trawlers and plastic injection moulding machines.

Which types of radial piston motors are there?

Generally, there are two basic types of radial piston motors. These are explained further here.

Crankshaft radial piston motor

The Crankshaft radial piston motor has a single cam and pistons pushing inwards. Moreover, it has an extremely high starting torque and is available in single displacements from 40 cc /rev through to about 5400 cc/rev. In addition, the Crankshaft type radial piston motors can run at [creep" speeds. And, some can run seamlessly up to 1500 rpm with virtually constant output torque. To sum up, the Crankshaft radial piston motor is the most versatile hydraulic motor.

Multilobe cam ring design

This type is constructed with a cam ring, which has multiple lobes and piston rollers that push outwardly against the cam ring. In essence, this produces a very smooth output with high starting torque. However, they are often limited in the upper speed range. Moreover, these high power motors are particularly good on low speed applications.

Other types of radial piston motors include: compact radial piston motors, dual displacement radial piston motors and fixed displacement radial piston motors. And in addition, we can also help you source: low speed high torque radial piston motors, two speed radial piston motors and variable displacement radial piston motors.

How do hydraulic gear motors work?

Gears are used to reduce the shaft output speed for applications that require a lower speed. This means that the Gear Motor`s operating pressure typically is very low, ranging between 100 and 150 bar. In addition, some of the more modern gear motors operate at, up to, 250 bar continuous pressure. However, the downside is that this motor can be rather noisy.

To sum up, gear motors are generally lightweight and small units with relatively high pressures. In addition they are known for their low cost, variety of speeds, broad temperature range, simple design and large viscosity range.

About hydraulic vane motors

Hydraulic vane motors are used in both industrial and mobile applications. For example, screw-drive, injection moulding and agricultural machinery. These motors tend to have less internal leaking than a gear motor. And subsequently, they are better to use in applications requiring lower speeds.

Hydraulic vane motors feature reduced noise level, low flow pulsation, high torque at low speeds and a simple design. Moreover they are easy to service and suitable for vertical installation. To function correctly, the rotor vanes must be pressed against the inside of the motor housing. This can be done through spiral or leaf springs. But rods are also suitable.

A vane motor typically features a displacement volume between 9 cc/rev to 214 cc/rev and a maximum 230 bar pressure. The speeds range from 100 to 2,500 rpm. Maximum torque of up to 650 Nm.

Learn more about axial piston motors

Axial piston motors use a bent axis design or a swash plate principle. The fixed displacement type works as a hydraulic motor and can be used in open and closed circuits. In contrast to this, the variable displacement type operates like a hydraulic pump.

In the bent axis design, pistons move to and fro within the cylinder block bores. This movement is converted into rotary movement via the piston ball joint at the driving flange. In the swash plate design, pistons move to and fro in the cylinder block. Subsequently it revolves and turns the drive shaft via the connected cotter pin.

What are the main characteristics of a gerotor motor?

Low speed, high torque (LSHT) hydraulic Gerotor motors feature a high starting torque and large range of speeds with a continuous output torque. In addition, the motor has a good power-to-weight ratio and a smooth operation, even at low speeds. The Gerotor motor`s design is furthermore very robust and built for harsh working conditions.