Compressed Air Treatment
Common questions – information
What are the main sources of contamination in a compressed air system?
- The atmospheric air
Air compressors draw in vast volumes of air from the surrounding atmosphere which contain large concentrations of airborne contaminants.
- The type and operation of the air compressor
The air compressor can also add contamination from wear particles to coolants and degraded lubricants.
- Air receivers and piping system
The air receiver and system piping stores and distributes the compressed air but will also retain the large amounts of contamination drawn into the system. Additionally they cool the moist compressed air to cause condensation on a large scale. This will promote corrosion, poor performance and potentially the buildup of sources of microorganisms.
Particulate contamination in a compressed air system is a combination of atmospheric dirt, microorganisms, rust and pipe scale. Atmospheric dirt and microorganisms exist in the large volumes of compressed air drawn in and rust and pipe scale occur due to corrosion of the compressed air system.
The dirt and rust can cause blockage or damage to the production equipment and of course if a few microorganisms were to enter a clean sterile environment enormous damage could be caused.
In a compressed air system water exists as water vapor, condensed liquid water and water aerosols. Of the main contaminants found in a compressed air system water is either directly or indirectly responsible for the majority of problems experienced by the compressed air user.
The water vapor enters the system through the compressor intake. The compression procedure causes the condensation of a large amount of the water vapour which has to be removed. Even after that removal there might be occasions where further local cooling of the compressed will have as result more water vapour to be condensed.
Water in any form must be removed to enable the system to function correctly and perform efficiently.
Oil is introduced into the compressed air system either through the compressor intake as a vapour or by the compressor as a liquid or as an aerosol (fine mist). The atmospheric air contains oil in the form of unburned hydrocarbons and its concentration can vary betwwen 0,05 and 0,5mg per cubic meter. On the other hand a typical concentration of 2 – 5mg per cubic meter enters the system from the oil used as lubricant from the compressor itself.
The main problems with oil in the compressed air system are due to the oil mixing with water already present. At this point the oil has lost its lubricating properties often becoming very acidic, which causes severe corrosion problems.
There are three standards currently in use which directly relate to compressed air quality (purity) and testing but the most commonly used standard is the ISO 8573 series and in particular the ISO 8573-1. According this part the compressed air quality is defined by three figures, e.g. 1.1.1. known as classes of compressed air.
The first number identifies the particulate content of the compressed air
The second number identifies the liquid water or vapor water content of the compressed air.
The third number identifies the total oil content of the compressed air.
According to ISO 8573-1 a class 1.1.1 compressed air represents the highest quality of compressed air with specific limits of contamination.
Class 0 for each type of contaminant also exists and it allows the user and an equipment manufacturer or supplier to agree their own levels which typically should be more stringent than class 1.
How can I specify the equipment for compressed air treatment based on ISO 8573-1.
This information should be provided by the equipment manufacturer and it is his responsibility to prove that his equipment complies with the requirements of the ISO 8573-1.