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The design and working principle of the vane air motor

Vane air motors are produced with power ratings up to approximately 5 kW. It has a basic design and consists of only a few components.


– A slotted rotor rotates eccentrically in the chamber formed by the cylinder and cylinder end plates.
– Since the rotor is off-center and its diameter smaller than that of the cylinder, a crescent-shaped chamber is created.
– The rotor slots are provided with vanes that move freely to divide the chamber into separate working chambers of different sizes.
– As a result of the centrifugal force, which is often reinforced by the compressed air, the vanes are forced against the cylinder wall to seal the individual chambers.
– The actual efficiency of these seals is a function of what is called ”internal leakage”.

Vane air motor components

1. Front end plate
2. Rotor
3. Vane
4. Cylinder
5. Rear end plate

Working principle

Air motor working principle

Working principle of an air motor

A. The air enters the inlet chamber “a”. Vane 2 has just sealed off the chamber “b” between itself and vane 3. The pressure in chamber “b” is still the inlet pressure. This pressure acts on vane 3, moving it in a clockwise direction.

B. The vanes have rotated further and the expansion process in chamber “b” has started. The pressure in it is thereby reduced but there is still a net force moving the rotor forward as the area of vane 3 is larger than the area of vane
2 in chamber “b”. Furthermore the inlet pressure acts on
vane 2 in the inlet chamber “a”.

C. The vanes have moved further. Chamber “b” is now being emptied through the outlet and there is no more contribution from this chamber. The force moving the rotor forward now comes from the force on vane 1 and vane 2.

Thanks to this simple principle the energy of the compressed air is converted into rotational motion from chamber to chamber, and the motor turns.