Different Air Compressor Types
Reciprocating Air Compressor
A reciprocating compressor is made up of a cylinder and a piston. These types of compressors work by positive displacement which means that they increase the pressure of the air by reducing its volume. Air is admitted into a cylider where it is raised to a higher pressure by the movement of the piston higher into the cylinder.
The piston and cylinder may be air cooled or water cooled. Water cooling is used on larger and more expensive units. This cooling action is important to increase compressor life and to keep maintenance and repairs low.
Multiple stage compressors have two pistons. The first stage compresses the gas to an intermediate pressure. The gas is then cooled before it enters the second stage which raises the pressure higher. Two stage units are more efficient and have cooler operating levels, which increases compressor life.
A consumer type small air compressor has a useful life of about 1,000 hours.
Rotary Screw Air compressor
A rotary screw compressor uses the rotation of two close fitting helical-lobe rotors that turn in synchronous mesh to produces a series of volume-reducing cavities. Gas is drawn in through an inlet port in the casing, captured in a cavity, and then compressed as the cavity reduces in volume. The compressed gas is then discharged through an outlet port.
In lubricated units oil is injected into the cylinder where it both lubricates and cools. The oil film also forms a seal to reduce back slippage of the compressed air. On non-lubricated types, timing gears are used to drive the rotors and multistaging is necessary to prevent gas temperatures from going too high. No portable air compressor for consumer use is rotary type.
Centrifugal Air Compressor
Centrifugal compressors produce high-pressure discharge by dynamic displacement. The compression action is accomplished when the gas enters a chamber with a rapidly spinning impeller. The gas is accelerated as it flows in an outward direction. This gas velocity is then transferred into a pressure rise and then to the output port. No portable air compressor uses this method.
One of the drawbacks of this type of compressor is its inability to deliver part-load flow at overall efficiencies as high as other types of compressors. Many people consider the centrifugal machine a base-load machine. Centrifugal compressors are usually designed for higher capacity uses because flow through the compressor is continuous and not well regulated.