How does an air motor work ?

19 mars 2019

Motor technical characteristics

Thanks to their flexibility and adaptability, air motors can be used in many contexts and applications. In this other  article, we explain how to choose the right pneumatic motor in three easy steps. It is really important as the productivity will depend on it. Hereafter, we will try to give you all the keys to understand the basics of air motors. 

We can spread the geared air motor in two distinct parts:

  • - The pneumatic part that allows the motor to run thanks to the compressed air expansion that applies pressure to the different elements

  • - The gear part that enables to adjust the speed and torque to the application requirement

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1. Pneumatic part

The pneumatic part is first made up of a stator (cylinder) which contains an eccentric rotor and is closed both ways by two flanges.

The existing space between these two parts has a crescent shape and the rotor has slots where the valves will be able to move.

When the rotor rotates, and thanks to the centrifugal force, the valves are pressed against the internal surface of the stator which splits the space into different chambers containing different volumes of air.

When 4 to 6 bar pressurized air is blown inside the pneumatic motor it enters the compression chamber. Each wall of this chamber will be therefore subject to a force proportional to its surface.


The rotor will rotate thanks to the different forces acting on the walls of the different surfaces defined by the valve. The volume inside the compression chamber will then increase which brings the air within to expand. It goes on and on for the next compression chamber which is in turn submitted to pressure. This process allow the ongoing rotation of the rotor.

This rotation motion then brings the chamber into exhaust position, releasing the air outside of the motor. It is this succession of pressurization which enables  motors operation.

Reversible motor:

In order to drive the rotor into the opposite direction, it is only necessary to move the point of air injection. This will bring the motor to rotate into the opposite direction.


2. Planetary gear reduction part

The rotor will rotate at a speed of about 10 to 20,000 revolutions per minute (rpm)  if under a pressure of 6 bars. The main role of the planetary gears is to adapt the movement to the needs of the application. The gear will therefore be chosen depending on the end use application of the motor.

Select the gear in relation to the end use

Every motor is unique as each outcome depends on the combination of pinions. This gives the rise to a large range of speed and torque.

It is possible to install several  gear steps, 1 to 5 depending on the range of the pneumatic motor.

A compressed air motor is totally flexible

The relationship between speed and torque is really important and easy to understand when talking about air motors. When there is no load the torque will be at 0 and therefore the speed will hit its maximum. As the load increases, the torque increases too and the speed decreases.

When the applied load exceeds the motors maximum torque, it causes the latter to “stall” . This maximum torque is referred to as the stall torque.

Pneumatic motors can therefore be used with different settings (torque/speed) in many applications.

Our client’s experience told us that most applications need a low speed combined to a high torque. Nevertheless, here at Mode, we are able to make every combination possible.

In addition to the almost endless capabilities in terms of settings, pneumatic motors are also highly adaptable to your working environment with the use of straight motors or with a right angle head and also remote control options.

If you want to know more about pneumatic motors, do not hesitate to download our handbook for free! Or request a free consultation in order to explain us your project !


Marie-Charlotte Messier
Marie-Charlotte Messier

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