SLIDING AND ROTARY VANE COMPRESSORS

The volumes between an eccentric rotor and sliding vanes will vary with angular position, to provide a form of positive displacement compressor (Figure 4.26). Larger models have eight or more blades and do not require inlet or outlet valves. The blades are held in close contact with the outer shell by centrifugal force, and sealing is improved by the injection of lubricating oil along the length

Figure 4.26 Sliding vane compression

Of the blades. Rotary vane machines have no clearance volume, but they are lim­ited in application by the stresses set up by the thrust on the tips of the blades. Whilst they have been used at low discharge pressures such as the first stage of a compound cycle, they are no longer widely applied in refrigerant compression.

Sliding vane or rolling piston compressors have one or two blades, which do not rotate, but are held by springs against an eccentric, rotating roller. These compressors require discharge valves. This type has been developed exten­sively for domestic appliances, packaged air-conditioners and similar applica­tions, up to a cooling duty of 15 kW (see Figure 4.27).

Figure 4.27 Rolling piston compression

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