3 - Air compressors, air treatment and pressure regulation

Abstract

Pneumatic systems use a compressible gas, hydraulic systems an incompressible liquid, which leads to some significant differences. The pressure of a liquid may be raised to a high level almost instantaneously, whereas pressure rise in a gas can be distinctly leisurely. The vast majority of pneumatic systems use compressed atmospheric air as the operating medium. Unlike hydraulic systems, a pneumatic system is “open;” the fluid is obtained free, used, and then vented back to atmosphere. Pressure in a hydraulic system can be quickly and easily controlled by devices such as unloading and pressure regulating valves. Fluid is thus stored at atmospheric pressure and compressed to the required pressure as needed. The slow response of an air compressor, however, precludes such an approach in a pneumatic system and necessitates storage of compressed air at the required pressure in a receiver vessel. The volume of this vessel is chosen so there are minimal deviations in pressure arising from flow changes in loads and the compressor is then employed to replace the air used, averaged over an extended period of time. Often, air in the receiver is held at a slightly higher pressure than needed to allow for pressure drops in the pipe lines. A local pressure regulation unit is then employed with the secondary air treatment close to the device using air. Composite devices called service units comprising water separation, lubricator, and pressure regulation are available for direct line monitoring close to the valves and actuators of a pneumatic system.