What is the working principle of an air motor?
The vane motor has a specific design and consists of only a few components
There are several types of pneumatic motor. The most used types are vanes, piston, and turbine motors. This article deals with vane motors only. Vane motors are produced with power ratings up to approximately 5 kW.
- Front end plate
- Rotor
- Vane
- Cylinder
- Rear and plate
- Bearing
Design
What is working principle of the vane air motor?
Thanks to this simple principle the energy of the compressed air is converted into rotational motion from chamber to chamber, and the motor turns.
- 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.
Clockwise / counterclockwise/ reversible
Working principle of an air motor | reversible motors have three air ports
Rotor speed
During starting and at slow speeds, some of the compressed air flows under the vanes to press them against the cylinder wall and seal the various working chambers. When the rotor rotates, the vanes are forced against the wall of the cylinder by centrifugal force. At high speeds, however, the pressure exerted against the wall by the vanes must not be too great, or excessive wear will result.
The amount of wear is a function of the third power of the sliding speed between the tip of the vane and the cylinder wall and, in actual practice, this determines the maximum rotational speed.
To keep the centrifugal force down, high-speed motors, or rather their rotors, are long and slim and equipped with only three or four vanes.
Number of vanes
During starting and at slow speeds, some of the compressed air flows under the vanes to press them against the cylinder wall and seal the various working chambers. When the rotor rotates, the vanes are forced against the wall of the cylinder by centrifugal force. At high speeds, however, the pressure exerted against the wall by the vanes must not be too great, or excessive wear will result.
The amount of wear is a function of the third power of the sliding speed between the tip of the vane and the cylinder wall and, in actual practice, this determines the maximum rotational speed. To keep the centrifugal force down, high-speed motors, or rather their rotors, are long and slim and equipped with only three or four vanes.
The number of vanes in the motor depends on which application the motor is designed for.
Gears
The rotor of a vane motor turns at quite high speed.
The free speed of a motor is typically around 20 000 rpm. For most applications, these speeds are too high, and the rotor torque is also small. To convert a high speed and low torque to lower speed and higher torque, gears are used.
Chicago Pneumatics' vane motors are supplied with several types of gears: planetary gears and helical gears.
Lubrication free motors
The traditional vane motors are lubricated by the compressed air to which a small amount of oil is added. Lubrication free motors are specifically designed to last longer and deliver better performances without lubrication. These motors are equipped with vanes made of a special low friction material and have permanently lubricated bearings. When long service life is the priority lubricated motors should be chosen because their vanes last longer.
- a. Motor
- b. Motor housing
- c. Planetary gear
- d. Output shaft
On which markets are air motors used?
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