Screw compressors
The most widely used types of screw compressor this oil-injected two-rotor machines (Fig. 13) and one screw machine, in which the main rotor grids with two diametrically opposite asterisks (Fig. 14). Screw compressor piston machine, able to act much higher pressure ratios than those of a reciprocating machine. They, due to their number of moving parts, ideal for heavy duty call for extended operation under high loads. Unlike piston machines, screw, machine operates on a specific internal pressure ratio is determined by its physical construction/geometry.
For optimum efficiency, the internal pressure ratio is determined by dividing the volume of the compressor must match the 'external' existing pressure drop across the cooling system. Modern screw compressors have the opportunity to constantly adjust their internal geometry, to ensure that the volume ratio of the results of the internal pressure ratio, corresponding exactly to external pressure drop at various head pressure.
Screw compressors are cooled oil that is injected into a machine for sealing operating clearances between the rotors and the housing.
It absorbs a significant amount of heat of compression. For optimal efficiency of the oil is cooled from outside the vehicle in a shell and tube heat exchanger cooled by water or refrigerant or thermo-siphon cooling. Cooling by direct injection of refrigerant in the compressor reduces the amount of available machines and corresponding loss in efficiency.
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Compressors 