Les hélico compresseurs ou compresseurs à vis

Abstract

In the first part of the paper the patenting of the helical compressor at the end of the last century by a Swedish engineer as a type of air and gas blower, modified some 50 years later by another Swedish engineer as an air and gas compressor, is discussed. Decade by decade, the machine was developed by the Swedish firm SRM and by their licenced manufacturers machining the screw compressor in Sweden, Germany, France, Scotland, etc. At the present time this type of compressor seems to be fully developed and occupies a first class position in the range of positive displacement machines. Recently, a new type of screw compressor has been patented by a French engineer, this machine having only one main rotor and two small satellites, compared with the early type which had only two main rotors. These two types of compressors are now competing on the refrigeration market all over the world. In the second part of the paper, all the improvements made during the 50 yeats of development are examined in detail. In the beginning, the screw compressor was designed as an oil free compressor and was not very well adapted to the refrigerating plants, this type of oil free compressor still being used for the compression of pure gases. The first improvement was the oil injected screw compressor allowing the machine to support high compression ratios and large pressure differences and some time later, to be fitted with a sliding valve for the purpose of volume adaptation. One other modification to the profile of the rotors results in greater compressor efficiency allowing it to work with higher compression ratios; for example, in the case of low temperatures such as are used for the freezing of food products. This is not a good solution for saving energy, and the performance has been improved by creating a complementary orifice designed as a superfeed port. This increases the global efficiency of the whole circuit with a screw compressor. The same improvements were carried out on the mono rotor screw compressors and now the two types of compressors are competing with the same auxiliaries imposed by the special lubrication of this type of machine. Some comparisons are made with reciprocating and centrifugal compressors.