The principle of rotary screw air compression is really no different than reciprocating (piston) compression. Both are positive displacement machines that take in a fixed volume of air at atmospheric press.
[pdf] The Variable Frequency Rotary Screw Air Compressor is an energy efficient solution for industrial air compression requirements. The motor output frequency is intelligently matched to air consumption, making it more energy efficient and longer lasting than traditional air compressors.
[pdf] Due to the growing need for the compressed air of higher quality, the water-lubricated twin-screw compressor with water as the only liquid in the compressor has drawn much attention to produce clean air a.
[pdf] 
