Air motor or electric drive - which one makes sense?
An air motor drives tools and machines with compressed air and outperforms electric drives where they reach their limits. This guide shows when compressed air pays off and how to size torque, speed and air consumption at a typical 6 bar.
View air motorsWhen does an air motor beat an electric drive?
An air motor converts the energy of compressed air into rotary motion. Its biggest advantage: it can be loaded all the way to standstill without damage and delivers maximum torque when stalled. An electric motor would overheat under the same blockage.
Because no electric current flows inside the motor, an air motor is spark-free and explosion-proof. In dusty, wet or hazardous (ATEX) areas that is often the deciding factor. It is also considerably smaller and lighter for the same power output.
- Overload safe: runs to standstill without overheating.
- Spark-free and ATEX-rated for hazardous zones.
- High power density: small, light, strong torque.
- Infinitely variable via pressure and air flow.
- Drawback: lower efficiency, compressed air is expensive energy.
How do you size torque and speed correctly?
Torque and speed of an air motor depend directly on the working pressure and the air flow. The characteristic curve is distinctive: the starting or stall torque is highest, while peak power sits at roughly half the free speed.
For sizing this means: choose the motor so that the operating point is near maximum power, roughly at 50 percent of the free speed. A gearbox matches speed and torque to the application - high speed for grinding, high torque for tightening and mixing.
- Determine the required torque from the application (Nm).
- Set the speed needed at the tool (rpm).
- Estimate power P = M x n / 9550 (kW).
- Pick motor and gearbox so the operating point is near P_max.
Which designs exist and how are they maintained?
Vane motors are the most common: compact, high speed and good starting behaviour. Gear motors deliver high torque at lower speed, while turbine motors reach very high speeds at low torque for grinding and drilling spindles.
- Supply clean, dry and lubricated air via a service unit.
- A silencer on the exhaust port cuts the noise level noticeably.
- Inspect and replace the vanes as a wear part periodically.
Frequently asked questions
Why does an air motor not overheat when it stalls?
Because it does not turn electrical energy into heat. When the shaft is blocked, air simply stops flowing and the motor stands still at maximum torque without any damage.
At what pressure is an air motor run?
Rated power, speed and torque are usually specified at 6 bar at the motor inlet. Higher pressure raises power and air consumption, lower pressure reduces both.
How do I find the right motor size?
Determine the required torque and speed of the application, calculate the power from them and choose motor plus gearbox so the operating point is near maximum power at roughly half the free speed.
Does an air motor need lubricated air?
Vane motors do - they need a service unit with a lubricator. There are also oil-free designs for food or cleanroom applications, but these cost more.
Looking for the right air motor?
We supply vane, gear and turbine motors with gearboxes and service units - sized to your torque and speed requirements.
Overload safe
Stall-proof and spark-free, even in hazardous areas.
Correctly sized
Torque and speed matched to your operating point.
Fully available
Motor, gearbox and service unit from one source.
Expert advice
Our specialists help with selection and sizing.