Air Motor – How it’s Designed and How it Works

The air motor is designed with a few things in mind: versatile power and durable construction. As opposed to the traditional electric motor, it proves to be more efficient and effective across all applications.  

The air motor is built with a compact and lightweight design. Considering its powerful features, there is no wonder why the air motor has become the go-to choice for industrial uses across the board. There is no denying the vast opportunities associated with the air motor, but how does it really function?  

In this article, we’ll be covering all there is to know in regard to how the air motor is designed and how it works. Let’s dive right in! 

 Air Motor Design  

The air motor comes in a few different design specifications: vane, piston, and turbine motors. This article will focus solely on vane motors, a simple air motor design that produces power ratings of up to 5 kW.

The vane motor design is straightforward and consists of only a few essential components. Here are its most fundamental design elements: 

  • A main body composed of a cylinder and cylinder end plates. This is what is referred to as the chamber, which holds a slotted rotor that operates eccentrically.  
  • The rotor is positioned slightly off-center and thus, a crescent-shaped chamber is created.  
  • In the rotor slots, vanes are positioned that divide the main chamber into separate working chambers of different sizes.  
  • The centrifugal force created by the motor and reinforced by the compressed air in the cylinder forces each vane against the inner walls of the cylinder, sealing the individual chambers.  
  • The efficiency created by these tight seals is a function of what is referred to as “internal leakage.”  

 How the Air Motor Works  

The functionality of the air motor can be described in a few simple steps.  

  1. Air enters the inlet chamber, described as “a”. At the same time, chamber “b” was just sealed off by vane 2. The pressure created in chamber “b” is still inlet pressure. This inlet pressure then acts on vane 3, moving it in a clockwise direction.  
  1. At this point, the vanes have rotated further and the expansion process in chamber “b” has started. As the expansion happens, the pressure in chamber “b” is reduced. However, there is still a net force moving the rotor; this is a result of the area of vane 3 still being larger than the area of vane 2 in chamber “b”. Similarly, the inlet pressure acts on vane 2 in the inlet chamber “a”.  
  1. By now, the vanes have moved even further. At this point, chamber “b” is being emptied through the outlet and there is no further contribution from this chamber. The force moving the rotor forward now comes from the force on vane 1 and 2.  
  1. In the end, the compressed air is turned into rotational motion (centrifugal force) from chamber to chamber, and the motor turns.  

 Air Motor Design and Functionality Elements  

To get a better understanding of how the different aspects of the air motor work together cohesively, it can help to break them down piece by piece.  

  • Rotor Speed: In the vane motor design, speed is especially important to consider. Problems don’t arise at low speeds, but at high speeds, excessive wear can result from the pressure being exerted on the cylinder wall by the vanes. To prevent this, the rotors of high-speed motors are long, slim, and designed with only three or four vanes.  
  • Number of Vanes: Depending on the application the air motor is designed for, it may be equipped with anywhere from 3 to 10 vanes. As a general rule, the fewer the vanes, the lower the losses due to friction. With that being said, more vanes in a motor usually provides for an easier start and less internal leakage.  
  • Gears: Because of its efficiency, the rotor of a vane motor turns at relatively high speeds. Gears are used in order to convert high speed and low torque into lower speed and higher torque. At Atlas Copco, we supply our vane motors with both planetary gears and helical gears.  
  • Lubrication: Traditional vane motors are designed to incorporate a small amount of oil. However, we’ve designed Atlas Copco’s vane motors to be completely lubrication free. We’ve accomplished this by equipping each motor with vanes made of a special low friction material and permanently lubricated bearings.  


The air motor is designed for versatile use across a broad selection of industrial applications. It generates efficient force – especially considering how compact and lightweight it is in comparison to other motors. This has allowed for impressive and widely applicable performance capabilities. 

Its unique and efficient functionality have made the air motor an ideal choice of power for many of today’s applications. Are you looking for more information? If you have any questions about how the air motor might be used in your application, feel free to reach out to us anytime.