Air compressors basically operate on a simple idea: when air gets compressed, the volume goes down and the pressure goes up. The piston is how this compression happens, and typically, the compressor will have a reciprocating piston. There are rotating impellers within the compressor for certain types as well. Reciprocating pistons have crankshafts, connecting rods, pistons, cylinders, and valve heads. A source of power is necessary to get the unit to function. The power source is typically electric or gas. There is also a tank to store air within the unit.

At the top of each cylinder, the valve head containing the inlet and the discharge valve are available . These are essentially metal flaps that will open and close depending on what type of movement is necessary. When the piston moves within the cylinder, vacuums are created.

The difference in pressure between what is inside the cylinder and what is on the outside is what allows atmospheric pressure to get the inlet vale to come open. Air comes into the vacuum space area and gets compressed by the piston, which goes up now. Then the inlet value closes and the discharge valve opens instead. Compressed air is then stored within the tank, which increases air pressure in the machine.