An air compressor is a device that converts power (usually from an electric motor, a diesel engine or a gasoline engine) into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts. There are numerous methods of air compression, divided into either positive-displacement or negative-displacement types.
Types of air compressor 
- According to the design and principle of operation
- According to the number of stages
- Single stage compressor
- Multi stage compressor
- According to the pressure limits
- Low pressure compressors
- Medium pressure compressors
- High pressure compressors
- Super high pressure compressors
- According to the capacity
- Low capacity compressors
- Medium capacity compressors
- High capacity compressors
- According to the method of cooling
- Air cooled compressor
- Water cooled compressor
Positive-displacement air compressors work by forcing air into a chamber whose volume is reduced to compress the air. Piston-type air compressors use this principle by pumping air into an air chamber through the use of the constant motion of pistons. They use one-way valves to guide air into a chamber, where the air is compressed. Rotary screw compressors also use positive-displacement compression by matching two helical screws that, when turned, guide air into a chamber, whose volume is reduced as the screws turn. Vane compressors use a slotted rotor with varied blade placement to guide air into a chamber and compress the volume.
Negative-displacement air compressors include centrifugal compressors. These use centrifugal force generated by a spinning impeller to accelerate and then decelerate captured air, which pressurizes it.
Conventional air compressors are used in several applications 
- To supply high-pressure clean air to fill gas cylinders
- To supply moderate-pressure clean air to a submerged surface supplied diver
- To supply moderate-pressure clean air for driving some office and school building pneumatic HVAC control system valves
- To supply a large amount of moderate-pressure air to power pneumatic tools
- For filling tires
- To produce large volumes of moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or cement plant bag house purge systems).
Most air compressors either are reciprocating piston type, rotary vane or rotary screw. Centrifugal compressors are common in very large applications. There are two main types of air compressor's pumps: oil-lubed and oil-less. The oil-less system has more technical development, but is more expensive, louder and lasts for less time than oil-lubed pumps. The oil-less system also delivers air of better quality.
See also 
- Klenck, Thomas. "How it Works: Air Compressor". Popular Mechanics. Retrieved 30 July 2010.
- Compressor types: rotary screw, reciprocating, and vane compressors