Air compressors have relatively simple design and can be sized all the way from the extremely powerful to ones that can just drive small tools. They have few parts and hence last for a long time with little maintenance. The factors make them drivers of choice from heavy equipment on manufacturing shop floors, to cleaning areas in gas stations and now, inside homes and small garages as parts of handy gadgets.
An air compressor works by transforming electrical energy in to kinetic energy in the form of air that is held in a highly compressed space before sudden release. The energy released when the compressed air is let out can be used for inflation, cleaning under pressure, turning, generating torque, driving or other similar movement by force.

The principle of an air compressor's functioning is like that of an internal combustion unit. A crankshaft moves a piston through a connecting rod, in a linear fashion along the length of a cylinder in which it fits snugly. Air is drawn in through an open valve as the piston moves upwards, providing ample space for a high volume of air. The valve closes and the piston moves down, compressing the air. The latter has kinetic energy as it gains tremendous pressure because of the restricted space in to which it has been forced. The valve opens again to release the energy.

Cylinders may be placed in series, so that the compressed air is fed to an intake where it is compressed further. The pressure goes up further and hence the power is increased in proportion. All air compressors must have back up systems to release extra pressure in the event of a malfunction in the valve mechanism. This is required to prevent an accident such as in an explosion.

The efficiency of air compression depends on air temperature, atmospheric pressure and relative humidity. The rating of an air compressor therefore depends on ambient conditions. This aspect should be taken in to account if an air compressor is used in very cold weather, very wet weather or at an high altitude.

Oil is used to lubricate the piston as it moves inside the cylinder. Rings act as seals to reduce the amount of oil that can mix with the compressed air. Some oil contamination, especially in atomized form, will inevitably escape ring seals and hence a more secure oil containment design is required in case the compressed air energy source has to be completely free of oil. Painting and other functions related to finishing a surface have this kind of requirement as even a faint oil trace can affect appearance.

Air compressors have relatively few parts and hence require little maintenance. They last for years and are versatile and compact as well. This is why new uses for air compressors keep surfacing so many years after the first unit was built. Some models have a second cylinder and sizes can be adjusted at the design stage to increase the range of applications and uses.