Air motors

The performance of an air motor depend on the dynamic air supply pressure measured at the air motor inlet; we can therefore obtain the characteristic linear output torque/speed relationship simply by regulating the air.

• With the pressure regulator installed at the air inlet, there can be controlled the stalling torque.
• With the air flow regulator installed at the air discharge, there can be hold the static torque and set the motor’s speed

When choosing an air motor, the main specifications to consider are :

• the torque at maximum power in Nm
• speed at maximum power in rpm
• power in Watts
• starting torque in Nm
• no-load speed in rpm.

Every air motor has a no-load speed, which is obtained by inserting one or more reduction gears, depending on the desired reduction ratio between the drive unit and the output shaft.

At the maximum speed (“no-load speed”) the torque (“turning moment”) at the output shaft is zero, while the speed will decrease by an amount that is inversely proportional to the torque as load is applied.

The power in Watts that an air motor produces is simply the product of torque and speed.

Every motor has its own characteristic power curve, with maximum power occurring at around 50% of its no-load speed. The torque produced at this point is referred to as the “torque at maximum power”.

The power of an air motor is obtained from the following formula:

P = (π x M x n)/30

where

P = power in Watts

M= torque in Nm

n= speed in rpm

The torque at maximum power is the torque obtained at approximately 50% of the no-load speed, which corresponds to the maximum motor power.

The starting torque is the torque that the motor delivers to the output shaft under load with the maximum air supply.

The stall torque is the torque that the motor delivers to the output shaft when it stalls during rotation. The stall torque is therefore approximately twice the torque at maximum power.

– Find out more about air technology, download the eBook –

Reversibility is comparable to the reverse gear in a motor vehicle: in our case, when the air motor reverses its direction of rotation.

The motor motion must be reversed in certain applications that have to move in both directions, such as when driving conveyor belts. These cases need reversible motors, which have two air inlets, one for each direction of rotation.

– Find out how to activate the direction of rotation, download the eBook –

To choose an air motor properly, you need to find the “working point” that suits your application. This “working point” consists of the operating speed required of the motor under load and the torque demand at that speed.

If, for example, a non-reversible solution is required to operate at 1000 rpm with a torque of 2.5 Nm, refer to the performance curves of each motor model in the motor data sheet to identify the “working point”, which is indicated with a yellow dot in the graph for the data in our example.

The motor to choose will be the one for which “the working point” is closest to the torque at maximum power (indicated with a red dot in the graph). If necessary, one method of obtaining the “working point” is to adapt the supply pressure by applying the motor performance variation coefficients.