Knowing the required torque is critical to choosing the right air motor, but it isn’t always easy to measure the torque you want as there can be many different factors to take into account!  

That said, there are a few key indicators that can help you to make a pretty accurate measurement…

What is the motor for?

Probably the first thing to consider is what the motor will be asked to do – and then work backwards from there. 

So, if the pneumatic motor will be asked to power a lifting application, such as a crane, you need to ascertain the weight to be lifted, the dimension of the gears and wheels in the system, and from there it’s a relatively simple engineering calculation.

Alternatively, if the motor is to be used for opening and closing a system, first consider whether the system can be manipulated by hand or not. If it can, then again it is reasonably easy to gauge the amount of torque that can be applied manually by an operator, which will give a good indication of the torque required.

Also look at the dimension of the motor’s shaft as this again gives an indication of the desired torque. For example, it the shaft diameter is 10mm, then you won’t be looking at a torque of 1000Nm! Similarly, the size of the motor’s gearbox provides key information regarding the strength of torque that the gearbox can handle.

Required torque versus maximum torque

It is important to bear in mind that there are two types of torque that come into the equation – the torque required for what you want your machine to do and the maximum torque the air motor can provide.

The motor may not need a high torque in the normal running of the application, say for mixing paint. However if the tool’s propeller mixing the paint gets blocked for any reason, then the torque applied to the motor will be equal to the maximum torque of the motor. Should this scenario happen, you need a system capable of withstanding the motor’s maximum torque in order to avoid damaging your equipment and to prevent any risk of injury to the operator.

Similarly, if you want a very low speed, you will choose a motor with a high reduction ratio, hence with a high maximum torque, so it’s necessary to take steps to protect the equipment from damage. One solution is to insert a sort of “mechanical fuse” between the motor and the machine that can be a part that is easy to replace and designed to break first in case of a too high torque.

Other options

You can also measure the static torque by using a simple torque wrench.

Here at Modec, we have a test bench which we can use to work out the torque value of your motor. It’s an easy process, so don’t hesitate to ask!