Oil separator
Short definitionA component in the discharge line that catches the compressor oil carried along with the vapour and returns it to the crankcase. It stops oil collecting in the pipework and the evaporator.
Along with the vapour it discharges, the compressor sends some oil into the system. If that oil stays in the evaporator, heat transfer suffers and capacity drops. If it does not come back, the compressor runs short of oil and the bearings seize. The oil separator splits the oil from the vapour at the compressor outlet and returns it to the crankcase through a float mechanism.
In small medium-temperature rooms with short lines and a single evaporator, the oil returns by itself if pipe sizes and gas velocity are right, and no separator is needed. It becomes mandatory when the line is long or rises, when evaporation falls to −25 °C and below, in multi-compressor central systems and with screw compressors. Selection looks at compressor capacity, refrigerant and discharge line size. Central systems add an oil reservoir and level regulators.