a two - stage screw compressor has a low - pressure stage screw compressor and a high - pressure stage screw compressor integrally constructed . compression space is formed by a male rotor and a female rotor , and operation gas is fed for compression to the compression space . a method of supplying lubrication oil prevents degradation of volumetric efficiency caused by return of lubrication oil , coming from a bearing and a shaft sealing device , to the low - pressure stage screw compressor . as a result , refrigeration capacity is improved and the amount of the lubrication oil is reduced .