From the standpoint of speed and pressure heads one can, in a general fashion, classify compressors as follows:
- Reciprocating – low speeds generating both moderate and high pressures
- Centrifugal – high speeds and moderate pressures
- Axial flow – very high speeds and low pressure
- This picture of compressor operation is portrayed in Figure 19.1. The temperatures o the compressed fluid are usually kept below 600°F and for this intercoolers are often required. the drives employed are shown in Figure 19.2, along with compressor mass flows; the flows are high at low speeds and low at the higher speeds. Thus bearings in compressors operate at speeds up to 30,000 rpm and, in some unusual applications such as in cryogenic pumps, may reach speeds of 100,000 rpm.