Common wrong understanding related to compressed air treatment

From: CAGI
publisher: Sean Wu
Time: 2017-02-19
Summary: Here are some common misunderstanding related to compressed air treatment from CAGI.

Here are some common misunderstanding related to compressed air treatment from CAGI.


1. Should filter elements only be changed when differential pressure is high ?

You install compressed air filtration to improve air quality. DP gauges/indicators are blockage indicators not air quality indicators. To ensure your compressed air quality, filter elements should be changed annually in line with manufacturer's instructions.


2. Are Coalescing filters  ONLY for oil removal ?

Coalescing filters have a even higher capture rate with solid contaminants than with liquids.


3. Is oil contamination  present in atmospheric air ?

Atmospheric air typically contains between 0.05mg/m3 and 0.5mg/m3 of oil vapor from sources such as car exhausts and industrial processes. As oil free compressors use large quantities of atmospheric air and atmospheric air contains oil vapor which can cool and condense in the compressed air systems, the use of oil free compressors does not guarantee oil free air.


4. Are liquid oil and oil aerosol the only contaminants present in a compressed air system?

Generally, there are ten contaminants found in a typical compressed air system that need to be removed or reduced for the system to run efficiently.

The ten contaminants are:
  Water vapor
  Liquid Oil
  Oil vapor
  Rust Atmospheric Dirt
  Water Aerosols
  Mirco organisms
  Oil Aerosols
  Liquid Water
  Pipescale

Only two of these contaminants, liquid oil and oil aerosol are introduced by a lubricating compressor. The purification equipment required to reduce, or remove the remaining contaminants by virtue of their operation also remove liquid oil and oil aerosols. Therefore regardless of the type of compressor installed, purification equipment is required.


5. Is Compressed air contamination a compressor issue ? 

In a typical compressed air system, compressed contamination comes from four different sources, these being:

Source 1 - Atmospheric Air
Air compressors draw in huge amounts of atmospheric air, which continuously fills the system with contaminants such as water vapor, micro-organisms, atmospheric dirt & oil vapor.

Source 2 - The Air Compressor
In addition to the contaminants drawn in through the compressor intake, the compressor also adds additional wear particulates from its operation. Additionally, oil lubricated compressors carry over liquid oil, oil aerosols & oil vapor from the compression process. Once through the compression stage, the after-cooler will also condense water vapor, introducing it into the compressed air in both a liquid and aerosol form.

Source 3 - Compressed air storage devices

Source 4 - Compressed air distribution piping

The air receiver (storage device) and the system piping that distributes the compressed air around the facility both store large amounts of contamination. Additionally, they cool the warm, saturated compressed air which causes condensation on a large scale, adding liquid water into the system. This saturated air and liquid water leads to corrosion, pipescale and microbiological growth.


6. Are Static Oil Water Separators are suitable for synthetic lubricants ?

Oil Water Separators are designed to reduce oil in water levels to acceptable limits. Some lubricants such as synthetics / PAG's also contain detergents and additives to extend the life of the compressor. Oil water separators are not designed to remove detergents and additives. Oil in water content cannot be accurately determined from visual inspection and lab analysis should be used. Lab analysis on cloudy outlet water is the only way of accurately testing oil in water content and will show it is within acceptable limits.


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