Two-stage compression cycle

摘要

An object is to provide a two-stage compression system that has no need for oil equalization between a lower-stage compressor and a higher-stage compressor, which makes it possible to simplify the configuration, and that makes it possible to reliably ensure appropriate oil levels in both the lower-stage compressor and the higher-stage compressor. In a two-stage compression system (1) in which a lower-stage compressor (2) and a higher-stage compressor (3) are disposed in series, and an oil separator (7) is provided on a discharge side of the higher-stage compressor (3), a first oil-returning circuit (11) and a second oil-returning circuit (12), which are independent of each other, are provided so as to be connected between the oil separator (7) and the lower-stage compressor (2) and the higher-stage compressor (3), and V1 > V2 is satisfied, assuming that the volume of oil returned to the lower-stage compressor (2) from the first oil-returning circuit (11) is V1, and the volume of oil returned to the higher-stage compressor (3) from the second oil-returning circuit (12) is V2.