Over the last few months, my EXAIR colleagues have blogged about several different types of air compressor types including single and double acting reciprocating and rotary screw. (You can select the links above to check those out.) Today I will review the basics of the sliding vane type, specifically the oil/lubricant injected sliding vane compressor.
The lubricant injected sliding vane compressor falls under the positive displacement-type, the same as the other types previously discussed. A positive displacement type operates under the premise that a given quantity of air is taken in, trapped in a compression chamber and the physical space of the chamber is mechanically reduced. When a given amount of air occupies a smaller volume, the pressure of the air increases.
Each of the previous positive displacement type compressors use a different mechanism for the reduction in size of the compression chamber. The single and double acting reciprocating use a piston that cycles up and down to reduce the compression chamber size. The rotary screw uses two inter-meshing rotors, where the compression chamber volume reduces as the air approaches the discharge end. For the lubricant sliding vane type, the basic design is shown below.
The compressor consist of an external housing or stator, and the internal circular rotor, which is eccentrically offset. The rotor has radially positioned (and occasionally offset) slots in which vanes reside. As the rotor rotates, the centrifugal forces on the vanes cause them to move outwards and contact the inner surface of the stator bore. This creates the compression areas, formed by the vanes, rotor surface and the stator bore. Because the rotor is eccentrically offset, the volume of the compression area reduces as the distance between the rotor surface and the stator reduces. As the rotor turns counterclockwise, the vanes are pushed back into the rotor slots, all the while in contact with the stator surface. The shrinking of the compression area leads to the increase in air pressure.
Oil is injected into compression chamber to act as a lubricant, to assist is sealing, and to help to remove some of the heat of compression.
The advantages of the lubricant sliding vane compressor type is very similar to the lubricant injected rotary screw. A few key advantages include:
- Compact size
- Relatively low initial cost
- Vibration free operation- no special foundation needed
- Routine maintenance includes basic lubricant and filter changes
A few of the disadvantages include:
- Lubricant gets into the compressed air stream, requires an air/lubricant separation system
- Requires periodic lubricant change and disposal
- Less efficient than rotary screw type
- Not as flexible as rotary screw in terms of capacity control in meeting changing demands
EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.
If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
Diagram: used from Compressed Air Challenge Handbook