The original method for compressing air and other gases was by pushing a piston or plunger into a container. This is called positive displacement compression. It is still the preferred method for compressing gases for high pressure applications.

More efficient methods for producing high volume low pressure air have taken over the low pressure applications (less than 8 atm). When air pressure in the 8 to 35 atm (120 to 540 psi) is required, the piston, or reciprocating, compressor is still the answer.

The plastic bottle industry has set the standards for the reciprocating compressor industry. Oil free and oil injected designs are available.

Capacity FAD is the measure of free air delivery.