The principle of the oil separator is to use the different densities of oil and refrigerant to settle and separate the mixed gas of refrigerant vapor and mist lubricating oil discharged from the compressor through the special structure inside the oil separator, and then send the separated oil back to the crankcase of the compressor. According to the different internal structures of the oil separator, there are many forms such as washing oil separator, centrifugal oil separator, packing oil separator, filter oil separator, etc. Different forms of oil separators have different separation effects due to their different structures, mixture temperatures, and oil content.