For an air compressor to function, a solitary motor on the compressor converts electrical energy into kinetic energy, according to Popular Mechanics. Compressors increase air pressure by concurrently diminishing the size of the space holding the air, and this is done with two reciprocating pistons. As pistons move down, a vacuum is created above them.
Outside air at atmospheric pressure pushes open a valve and fills the area above the piston. Similar to small combustion engines, piston compressors have crankshafts, a connecting rod with a piston, a valve head and a cylinder. As the pistons pump up and down, more air enters the tank and pressure builds.
Compressors utilize a pressure switch to halt the motor if the tank pressure reaches a certain limit. Two different types of air compressors are available for purchase: single-stage and two-stage. The single-stage compressors usually operate in the range of 70 to 100 pounds per square inch gauge (psig), while two-stage ones are higher at 100 to 250 psig. The rate at which a compressor delivers air is measured in cubic feet per minute, but this will vary with atmospheric pressure. A basic measurement to keep in mind when using an air compressor is one horsepower is about four cfm at 100 psi.