PROVIDING OIL-FREE COMPRESSED AIR.

In selecting a compressor, two major decisions must be made: type of cooling - air or liquid (oil or water); and type of compressor operating principle - positive displacement or dynamic. These decisions may be influenced significantly when a requirement for oil-free air is added as a part of the system specification. It is difficult if not impossible to give specific guidelines for selecting a type of compressor for all oil-free applications. When the demand is small, the alternatives available to the plant engineer to choose from are broadest. The number of suitable units to choose from decreases somewhat with increasing demand. This article discusses six types of compressors that may be useful as a source of oil-free air: reciprocating, diaphragm, centrifugal, screw, lobe, and liquid ring.