Tuesday, December 23, 2008

Positive Displacement Compressors-Vane 2


Air Compression between sliding vanes is basically a simple concepts.

Compression takes place when the volume of the spaces between the sliding vanes in a rotor is reduces as the rotor turns or rotate within an eccentric cylinder (housing).

The distinguishing features of these type of rotary sliding vane compressors is the injection of liberal quantity of oil directly into the compression chambers:
1. To seal the cells,
2. Provide lubrication,
3. Cooling,
4. to absorb the heat of compression

Constructions and designs varies with different manufacturers, but the principles of operation and control are similar.

The rotor has 6 to 8 longitudinal slots in which, vanes slide freely, move outward by centrifugal force against the cylinder wall of the stator.

As the rotor rotates, each vane sets pass the inlet (Suction) port to form a cell (Chamber), between it and the preceding vane sets. The air, that is trapped is compressed as volume of the cell decrease until the leading vane of the cell pass the outlet (discharge) port.

With rotation counter-clockwise, the volume between the vanes, the rotor, and the stator is increasing between the inlet port, at right, and top.

Consequently, partial vacuum is created, cause it to sucks in more fresh air from atmosphere in through the inlet port. The volume then decreases as the cell approaches the outlet post at top left, causing the air pressure to rise. Air is not leak back around the rotor, because it is sealed between the rotor and its blades, concentric bore in the stator and compressor oil.

These positive-displacement have a fixed compression ratio for any given model. Ratios up to 10:1 can be used to compressed air in a single stage.

An important factor in obtaining high efficiency is the controlled oil injection into the compression chamber.

Oil is injected for:
1. sealing each cell from its' neighbour,
2. seal between the high=pressure and partial-vacuum conditions within the cycle,
3. cool the air been compressed,
4. Lubrication.

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