Compressors are machines that compress air or gas. Compression is achieved through the reduction of the volume that the gas (or air) occupies. As a side effect of the minimization of volume, the temperature of air or gas increases.

The higher the compression ratio, the higher the temperature tends to rise. However, compressor manufacturers do take this into consideration. The problem is resolved by compressing on a per-stage basis and simultaneously cooling the gas.

There are many compressor types. Different compressor types achieve different compression ratios. Moreover, the horsepower that different compressors can achieve varies from 1 to 2 HP (Horsepower), up to a few thousand HP. Some compressors require oil in order to operate while others do not.

The most important compressor designs are listed below.

Reciprocating compressors are equipped with a crankshaft, which drives the pistons. They are commonly found in versions that produce 5 to 30 HP. However, larger ones used for industrial purposes can produce up to 1,000 HP.

Centrifugal compressors are used for heavy industrial purposes. Centrifugal compressors produce from ~100 HP up to a few thousand HP. They are usually stationary, and one of their applications is small gas turbine engines.

Rotary screw compressors are compressors aimed at commercial use. Their horsepower varies from 5 to 500 HP, and they are usually employed as superchargers in automobile engines.

Diagonal/Mixed-flow compressors are similar to centrifugal compressors except for some technical characteristics.

Axial-flow compressors are mostly used in large gas-turbine engines.

Scroll compressors are not as efficient as rotary screw compressors. They can be found as superchargers in automotives.

Along with the uses listed above, compressors are used in fields such as jet engines, refrigeration, medicine manufacturing, SCUBA diving, turbochargers, submarines, and air conditioning.