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A Hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder.

Conceptually, a hydraulic motor should be interchangeable with a hydraulic pump because it performs the opposite function - much as the conceptual DC electric motor is interchangeable with a DC electrical generator. However, most hydraulic pumps cannot be used as hydraulic motors because they cannot be backdriven. Also, a hydraulic motor is usually designed for the working pressure at both sides of the motor.

Hydraulic pumps, motors, and cylinders can be combined into hydraulic drive systems. One or more hydraulic pumps, coupled to one or more hydraulic motors, constitutes a hydraulic transmission.

[edit] Hydraulic motor types

For an explanation of plunger and piston, see hydraulic cylinder

Many designs are possible. The following types of hydraulic motors are available:

[edit] Gear and vane motors

Gear and vane motors are used in simple rotating systems that may be used occasionally.

[edit] Axial plunger motors

For high quality rotating drive systems plunger motors are generally used. Whereas the speed of hydraulic pumps ranges from 1200 to 1800 rpm, the machinery to be driven by the motor often requires a much lower speed. This means that when an axial plunger motor (swept volume maximum 2 litres) is used, a gearbox is usually needed. For a continuously adjustable swept volume, axial piston motors are used. PISTON TYPE.— Like piston (reciprocating) type pumps, the most common design of the piston type of motor is the axial. This type of motor is the most commonly used in hydraulic systems.

[edit] Radial plunger motors

Radial piston motors can not be obtained with very large swept volumes. Sometimes because the total piston volume of the pump is large (up to 8-9 litres), sometimes because the pistons move more than one time each revolution (up to 250 litres working swept volume). By decreasing the swept volume of the motor, the speed increases and the maximum torque decreases. Radial motors can get an adjustable swept volume by switching off some of the plungers.

[edit] Braking

Hydraulic motors usually have a leakage connection, which means that a hydraulic motor in a drive system can never hold the load, like a hydraulic cylinder can. There is always a need for a brake or a locking device.

[edit] Uses

Hydraulic motors are used for winch and crane drives and as wheel motors for military vehicles, self-driven cranes, and excavators.

[edit] See also

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