Vane or rotary compressors consist of a cylindrical housing in which the rotor is eccentrically mounted. Longitudinal slots for holding the vanes are cut into this rotor. Upon rotation, the centrifugal force presses the vanes against the internal wall of the housing. Trailing rings contain the centrifugal forces of the vanes during rotation. The internal diameter of the trailing rings used, is made somewhat smaller than the internal cylinder or housing diameter. Vane compressors exist in oil lubricated and oil flooded designs. In both cases, the compressor oil serves not only for lubrication but also as a sealant between individual vanes and the housing inner wall.
Figure 3.3.2.1
For oil flooded vane compressors, a considerable quantity of oil is introduced into the compression chamber. This quantity of oil serves to conduct away the heat generated by compression so that the compressor output temperature amounts to only about T = 80-90°C. The injected oil is filtered through separators after compression and channelled back to the circuit after separation. On the other hand, oil lubricated vane compressors reach very high temperatures in the compression chamber, depending on the final pressure. Compression causes the compressor oils to crack to such an extent that the oil residues in the compressed air may still be filtered out, however, only at the expense of reduced service life of the downstream filter elements. The individual vanes, manufactured either from phenolic resin impregnated plastics or hardened steel, form cells within the rotor which, upon rotation, expand on one side and shrink on the other. On the intake side, the ambient air is drawn in through the enlargement of the cells and, through further rotation, conveyed to the pressure side. There, shrinking of the cells leads to continuous compression of the air. Vane compressors are supplied as ready to connect compact units. These single-stage, single shaft compressors can be installed without foundations. This type of compressor is usually fully equipped with aftercooler, separator and all necessary safety devices. Compressors of this design have no valves but, are fitted with an output control adapted to the desired output pressure.
Figure 3.3.2.2
Adaptation to the operating conditions takes place via intake regulation. If, at nominal operation of the compressor, the compressed air consumption falls, the pressure in the system rises. As soon as the pressure in the system reaches a preset value, a regulator causes an intake restrictor to become operative, thus reducing the volume drawn in, approximately in proportion to compressed air demand. The power consumption of the drive motor is harmonised with the operating conditions. The smaller the compressed air consumption, the more the system pressure rises. Once the limit value to which the pressure monitor is set reaches the maximum switching point, the regulating system opens an integrated discharge valve and the pressure in the compressor falls to about 3 bar. The compressor is separated from the network of points of use by a non return valve. On the intake side, the drawn in volume is set to the lowest value through restriction. The compressor now operates in a closed circuit or idle running, with minimum power consumption, which amounts to about 22% of the nominal consumption. Vane compressors, whether air or water cooled, find diminishing use for industrial applications. Maximum pressure is usually up to 10 bar gauge . The output is suitable for medium requirements.
