Published at Sunday, September 09th 2018, 04:59:47 AM by Sharlene Pittman. Air Compressor. All reciprocating air compressors throw out some oil with the air they compress. When the tank reaches its designed pressure limit, a switch will interrupt electrical power to the motor. Simultaneously, a certain amount of oily air will be released into the shop environment. You may see oil collecting on the wall behind the compressor and on the pump and compressor as well over time. This is not cause for alarm but periodic cleaning may be needed.