Rotary Screw Compressor
Much more efficient and even simpler -- is the screw compressor. The screw compressor is also driven by electric motors. The main difference from the piston type is that the screw compressor uses two large intermeshing screws to squeeze the air inside a large chamber. In order to keep the screws from being damaged, oil must be injected to keep the entire system lubricated.
The oil is mixed with the air upon entrance into the compression chamber and is passed between to two rotating screws. After exiting the chamber, the air and oil pass through a large oil separator where the air passes readily through a small orifice filter. The oil is cooled and reused while the air goes on to the reservoir tanks to be utilized in work.