The source of air in a typical pneumatic system is an electrically driven air compressor. Most pneumatic systems can be serviced with a compressor sized under 10 horsepower. The most efficient air compressors in this size range are piston-style reciprocating units.
Regardless of the design of the compressor, the need for clean, dry, and oil-free air is essential to ensure that the air lines, controllers, switches, relays, restrictors, and other components in the system remain clean and operate satisfactorily. For this reason, a number of related devices, such as coalescent filters and refrigerated driers, are necessary in a system to remove any oil vapors and dirt particles and to dry the air. Even the use of oil-less air compressors does not guarantee that oil will not be present in the system. Often, the compressor intake air may con~ oil vapors that can pass through the compressor and condense into harmful droplets in the system if removal devices are not employed.