Types of Hydraulic Motors

We can look at the types of hydraulic motors under 3 main headings:

Gear-Type Hydraulic Motors (Gear Motors)

Hydraulic motors that work with gears operate on the principle of fluid entering between the gear teeth, generating a certain torque, and rotating a shaft coupled to the gears.

Working system of a gear-type hydraulic motor (above)

External Gear Hydro Motors

This is a circuit component used to produce rotary motion, converting hydraulic energy into mechanical energy. Their construction and operating principle are similar to pumps.

Internal Gear Hydro Motors

Fluid entering the motor from the high-pressure zone applies pressure to the surface of the gears. If the pressure value exceeds the load value, the hydro motor starts to rotate. Both gears are designed to rotate freely.

Internal gear hydro motors have low speeds and a short service life. These properties limit their fields of use. They’re used in simple mechanisms, in places where high efficiency isn’t needed and torque requirements are low. They’re used more in automobiles and agricultural vehicles than in industrial systems.

Orbit-Type Hydro Motors

Despite their compact construction, these motors can produce high torques. As with gerotor motors, the outer gear doesn’t move. The inner gear, however, rotates.

Roller-Type Hydro Motors

This is the roller-based variant of orbit motors. Rollers are used to increase motor efficiency and make maintenance easier. Fluid sent into the motor applies pressure to the inner gear, generating a torque that tries to rotate the motor.

Piston Hydraulic Motors

Piston motors are divided into two types: radial and axial piston motors.

Axial Piston Hydraulic Motors

Below, the operation of an axial piston motor is shown. Axial piston motors have a high flow rate even at low speeds. They can start operating under high torques. They’re an ideal choice for high operating speeds.

Axial piston motors are made in two different types: bent-axis and swashplate. (below)

Radial Piston Hydraulic Motors

Below is an exterior view of a radial piston hydraulic motor. In radial piston motors, the pistons don’t operate on axes parallel to each other.

Radial piston motors can start operating with high torques. There can be torque ripple or fluctuations in operating speed at low speeds.

A radial piston motor with a fixed cylinder block and rotating shaft (above)

Vane-Type Hydraulic Motors

In vane hydro motors, the pressure the fluid applies to the vanes creates a force that drives the rotor to turn. The rotor’s motion is transmitted outward through the shaft. Vane motors have lower torque and a shorter service life compared to piston motors. They operate up to speeds of 1000 rpm. With good electronic control, speeds as low as 0.1 rpm can also be achieved.

The rotation of the motor shaft results from a pressure differential. It applies a force against the vanes across from it. This force is tangent to the rotor and causes the rotor, and along with it the motor shaft, to rotate.
If fluid is directed into the motor from the motor housing, the shaft, viewed from its end, rotates
clockwise. When the oil supply is instead directed to the cover port, rotation, viewed from the shaft end, is counterclockwise.
This is how the direction of fluid flow is changed.  This is usually done by a suitable directional control valve.

Parts of a vane hydraulic motor (above)

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