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What is a Hydraulic Motor?

By Jason C. Chavis
Updated May 17, 2024
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A hydraulic motor is part of a hydraulic drive system that uses pressurized fluid to move a cylinder and make a machine function. An electric motor, combustion engine, or some other type of generator, pressurizes hydraulic fluid through a series of valves and pipes to control the system. This fluid physically pushes either a hydraulic cylinder or motor and drives the machinery. The motor itself is the actuator that converts the fluid's pressure into torque and rotation.

Gears can be added to a hydraulic motor to change the level of torque administered to a specific operation. For example, a military vehicle that needs to travel over many different types of land will have different gears to control the amount of pressure used to push the motor. Pavement will need less hydraulic power to move the vehicle, while dirt or mud may need more.

Different types of plungers or pistons can be used in the motor. The most common type is an axial plunger. The pistons for the motor are designed to be parallel to allow for continuously adjustable sweeps to make the hydraulic motor operate more efficiently. The speed of the hydraulic motor ranges from 1200 to 1800 rpm. In order to increase the speed of the motor, radial pistons can be used. These pistons makes short sweeps in the engine, allowing for increased speed. However, the maximum level of torque decreases as an effect of these short sweeps.

One of the disadvantages of a hydraulic motor is that it allows for leakage through a connection in the drive system. This helps prevent the engine from locking up as it turns. This means that the motor needs some sort of braking mechanism to ensure that the system remains properly secure. It also requires routine monitoring of gauges that display the fluid levels. A safe operating system is important for the continued use of the machine.

First developed during the 1700s, hydraulic motors are notable for the fact that they can produce more power than other motors of the same size. They can take on larger loads than traditional electric motors and are most commonly used in aircraft, construction vehicles, and automobiles. In addition, a large volume of industrial machinery uses hydraulic motors to perform heavy lifting tasks and in situations that require strong pressurized actions such as injection molding. These can be constructed as small components to a complex mechanism or one very large hydraulic motor performing a single task.

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Discussion Comments

By Fiorite — On Nov 13, 2011

@Amphibious54- You could design an engine that uses hydraulic power to create propulsion, but you will still need a power source. Currently, the power sources available would be gasoline, diesel, hydrogen, or electricity. These fuels are all secondary fuels, so a hydraulic drive system would be a tertiary power source at best.

This tertiary drive system could prove to increase efficiency if it is used as a energy storage mechanism. A vehicle loses large amounts of energy when it brakes. This energy is lost as heat to the atmosphere and friction to the road. A hydraulic drive system could work to capture some of this lost energy and store it as hydraulic pressure (potential energy) in a large cylinder. This cylinder could then be used to help the vehicle accelerate under stop and go driving. The system would not be very useful for long highway driving, possibly resulting in a reduction in fuel economy because of the added weight of the system, but it could be very beneficial in delivery type vehicles that rarely hit the highway. I know that applications like this have been proposed. You might find some good resources with a little web search.

By Amphibious54 — On Nov 12, 2011

Could a hydraulic motor be used for propulsion in an automobile? Would a rotary hydraulic motor be capable of replacing an internal combustion engine? How exactly do rotary hydraulic motors work?

A teacher in my physics class asked us to write a short essay about an alternative to the internal combustion motor, but I have no idea where to begin. I was thinking about writing about an electric motor, but I think just about everyone in my class is going to write about that type of motor. I am not really one to follow the crowd. Can anyone explain to me if this is possible, and briefly how it would work? Thanks!

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