Air motor : which one to choose for what need and what use?

14 novembre 2017

Motor applications

Once you’ve determined the power of your air motor, to make the best choice, you should know the environment in which the motor will be used and the characteristics of the application. Air motors have a wide operating range. In many cases you’ll find several motors capable of meeting the same need in terms of power, torque, and speed.So how to choose the right motor and what are the selection criteria?

How to select the righ air motor.jpg


On this drawing you can see that for the speed and torque required you can choose any of the 3 air motors. Severals possibilities are correct.

So how to choose the motor that will fit the best your requirements?

Three criteria will allow you to choose the right motors, the one that will fit perfectly your application :

Maximize the energy efficiency ; assure a reserve power (in case of load increase) ; importance of stall torques and starting torques under load. 



Energy efficiency

energy efficiency air motor.png


To maximize an application’s energy efficiency, we will choose a motor that, given the required torque in operation at working point (C) provides a rotational speed (V) such that one is the closest to the motor optimal working point (PF) that has the maximum power (Pmax).


A power reserve


 If we want to maintain constant speed in case of torque increase, it is necessary to consider a power reserve. This is obtained by choosing an air motor with speed at working point, higher than the speed at maximum power (When speed is not stable, it may be necessary to consider limiting torque system in order not to reach maximum torque allowed on the air motor shaft).

In this case, we will choose a motor whose rotational speed at working point in normal use is greater than that of the motor optimal working point.

Thus, at the time of the hard point, the required torque will increase from C1 to C2 and the speed will decrease from V1 to V2, and the delivered power will increase from P1 to P2.


  • Be able to face a load increase without too much speed reduction
  • Keep power if load fluctuates.


Stall torques and starting torques under load

  • The stall torque is the maximum torque delivered by the motor. Some applications require ensuring a minimum stall torque. This is the case, for example, when using air motors for screwing, clamping, or closing doors (safety aspect), if we want to cope with transient overloads (jamming) or if we want to have a safety coefficient in relation to the available torque. Others require ensuring a maximum stall torque. This is the case when you want to be sure that the torque applied shall not exceed the mechanical resistance of the system (risk of breakage). In the absence of a torque limiter, it’s the stall torque that will ensure this function. This torque is graphically visible, and it is generally equal to 2 times the torque at maximum power.


  • The starting torque under load is an important factor, especially in the case of using the motor to lift a load (winch). This torque is not specifically graphically indicated, because it depends on the position of the vanes in the motor at startup time and can vary significantly depending on the quality of the motor lubrication. It is however at least equal to 70% of the stall torque. In this type of application, it is advisable to reduce the distance between the compressor and the actuator as much as possible.


The motor's working environment is also an important element to take into account when choosing the motor’s options and accessories:

  • The room temperature may vary from -30° C to +150° C with precautions on the drying of the air
  • The environment can be specific (humid, corrosive, explosive, radioactive, dusty, etc.). Our motors are made to work in harsh environments.
  • Release of air. Some applications may require motors to not cause any release of oil into the air. In these cases, there are specific filters and exhaust collectors.
  • Presence of water or liquid. Air motors are not sensitive to water (because there’s no electricity) and can even function underwater with certain precautions.
  • Supply with specific gases This case may require special precautions.


Once the choice is made by considering all these criteria, your air motor offers reliable and safe use. From the time where adjustments are made, the motor may be used without skills or specific certification.

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Bruno Martin
Bruno Martin

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