Because refrigerants and refrigeration oils are miscible in one another, there will always be some oil that leaves the compressor with the refrigerant being circulated. Also, any time flooding or migration occurs, crankcase oil is sure to be diluted with refrigerant. This will cause oil foaming at start-ups. Crankcase pressures will build often forcing oil and refrigerant around the rings of the compressor’s cylinders to be pumped into the discharge line.
Oil separators remove oil from the compressor’s discharge gas, temporarily store the oil, and then return it to the compressor’s crankcase. Oil separators are located close to the compressor in the discharge line. Even though most oil separators are designed to be mounted vertically, there are some horizontal models available on the market. Oil separators are essential on low and ultra-low temperature refrigeration systems and on large air conditioning systems up to 150 tons. Most compressor manufacturers require oil separators on all two-stage compressors. Oil separators can also act as discharge mufflers to quiet compressor pulsation and vibration noises.