All atmospheric air contains some water vapor, which will begin to condense into liquid water in the compressed air or gas system when the air or gas cools past the saturation point, i.e., the point where it can hold no more water vapor. The temperature at which this happens is known as the dew point.

Wet saturated air is a problem:

  1. As it cools while passing through the main distribution piping, more water will condense out. That water will pick up pipe scale and rust and carry them downstream to the final end uses.
  2. Many operations of process industries are dependent upon the proper functioning of pneumatic controls. The malfunctioning of these controls due to rust, scale, and clogged orifices can result in damage to product or in costly shutdowns. The corrosion of air operated instruments, can give false readings, interrupt or shut down plant processes.
  3. If the pipes are exposed to freezing temperatures, ice will form — in some cases, building up in large enough quantities to restrict the flow of air.

For the above reasons, Instrument air dryers are a necessary part of the compressed air system in a typical chemical plant.