Among other advantages over electric motors, air motors do not require "oversizing" in terms of power, first because there is no risk of overheating, and also because the displayed power of an air motor is the actual power output. This is not the case with electric motors that have a power output that is lower than the apparent power.
How to choose air motor's power? To determine the necessary power, you need to have in mind 3 pieces of information and it’s necessary to know the environment in which the motor will be used to narrow down the choices.
Pressure and available air flow
Available pressure and air flow will determine the power available for the motor. It is an essential element for the application. In general, air motors are designed to operate at a pressure of about 6 bars. If not, the motor will run, but with reduced performance (especially the torque).
This is the speed we want the motor to turn in "normal" conditions of use, meaning with the application’s nominal torque, the defined pressure, without special constraints (such as blocking or abnormal load applied to the motor). Unlike an electric motor, an air motor adapts speed depending on the required torque.
These 3 characteristics will determine the power required for the application. For a given pressure, the power is a function of the torque and speed by the following relationship:
P = (T x S) / 9.55
P = Power (in watts) T = Torque (in Newton meters) S = Speed (in revolutions / minute)
So, if we know at least 2 of these elements (power, torque, speed), we can determine the third!