Drying Pressurized Air

A component of atmospheric air is moisture that in compressed air systems after compression causes a condensation of oil and water vapor to become drops. The oil condensate has a strongly corrosive effect and is in most cases acidic.

Without an air preparation system, such as a compressed air dryer, a substantial proportion of the corrosive condensate would end up in the compressed air system. Corrosion of the pipelines, damage to the pneumatic tools and equipment, along with a possible negative influence on the quality of the final product could result.

The drying process draws moisture out of the compressed air. Dry compressed air lowers the risk of corrosive damage to the compressed air system and improves the cost effectiveness of the attached machines and tools.
Two processes are mainly used to dry compressed air: refrigerated drying and absorption drying.

Absorption Dryer

The absorption dryer is made up of two pressure vessels in which the drying agent is found, usually aluminum oxide, silica gel, or a mix of the two.
The compressed air flows through a chamber and is cooled by contact with the drying agent to a dew point of minus 25 °C (or lower). Most of the dried compressed air then flows directly into the compressed air system. A partial flow (3-15 %) is routed into the second tank where the compressed air is brought to atmospheric pressure. The dried, expanded air then removes the moisture from the drying agent in this vessel and vents it out into the environment.
After a certain amount of time, the vessels switch functions, and a continuous drying processes is possible.
The absorption dryer is sensitive to oil and water making a separating filter for oil and water necessary in front of the dryer.

Refrigerated Dryer

The refrigerated dryer consists of a cooling machine with a cooled compressor, heat exchanger and a coolant. The compressed air is cooled to 0 to +6 °C and the precipitated condensation water is automatically drained away.
Through the dryer the compressed air achieves a dew point of +3 °C to 10 °C. This is sufficient for condensate-free compressed air for use in heated spaces.
It is easy to install the dryer; it requires little energy and is comparatively immune to oil in the compressed air. An oil separator should be installed behind the dryer to reduce the amount of residual oil in the compressed air.

Advantages of compressed air dryers:
  • Lower costs for the compressed air supply system
  • Energy savings
  • Low maintenance costs
  • Longer service life
  • Greater productivity
  • Higher quality of the final product
  • Easy installation
  • Long maintenance intervals, low number of expendable parts
  • Huge energy savings
  • Ecologically friendly and quiet

Choosing a compressed air dryer:
When selecting a compressed air dryer with the right capacity, the following factors must be taken into consideration:
  • What temperature and pressure does the compressed air have prior to drying?
  • How quickly does the air flow through the dryer?
  • Which dew point is required after drying?
  • What is the temperature of the ambient air?

Classification of the compressed air quality

ISO norm 8573.1: the quality standard for compressed air
PNEUROP, the European association of manufacturers in the field of compressed air technology, has drawn up an ISO norm for the classification of compressed air in relation to the content of solid particulates, water and oil.

Typical requirements for the levels of compressed air quality according to ISO 8573.1

* The numbers refer to the numbers of the air quality classes in the table above. Please refer to the table for the appropriate information.

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