Single Stage, Oil-Free Screw Compressor with a Compression Ratio Eight

The development of a series of sin~le-stage, oilfree screw air compressors with a compression ratio of 8, previously obtainable only with two-sta~e compressors, is described. A new rotor profile, which reduces leakage loss to achieve higher efficiency, and desig-ned for ease of manufacture, is detailed. Additionally, a new desig-n method for the clearance between rotors, to compensate for rotor deformation due to thermal expansion, is also introduced. This oil-free, screw air compressor with a ratin? of 37-55 kW has been marketed since 1982 and 15-22 kW since 1984. INTRODUCTION Oil-free air compressors having a discharge pressure of approximately 0.8 MPa (8 ata), and widely used in electrical, food and chemical industries were traditionally reciprocating type compressors. Recently, however, the advantages of oi 1-free rotary screw compressors have been reco~nized. These include mechanical simplicity, high reliability,low noise and low vibration. Two-stag-e, oil-free screw air compressor use has predominated in the capacity range above 550 m3/h (motor power above 65 kW). Nevertheless, for compressor capacity below this range, where oil-free air is needed, this type of compressor was not available.