Compressed air is vital to many production processes. But did you know that up to 10 contaminants could be present in your supply? And this rises to 15 if using compressed air for breathing air applications.

Contamination can be introduced by atmospheric conditions, the compressor itself and during distribution, by the air receiver and pipework. The contaminants can be either solid or states.


Identification of contaminants

These are the 10 major players which could enter your compressed air system:

  1. Atmospheric dirt. How clean is the air around you? In an industrial environment, every cubic metre of air contains 140 million dirt particles on average. This can include dust and pollen. And 80% of these particles are less than 2 microns, making them too small to get captured by an intake filter.
  2. The bacteria and viruses we’re susceptible to picking up, can get drawn into the compressed air system. The warm, moist air is the favoured environment for the growth of microorganisms. Every cubic metre of air can contain up to 100 million microorganisms.
  3. Water vapour. The higher the temperature, the more water vapour that can be held by the air.
  4. Water aerosol
  5. Condensed water. In a standard compressed air system, up to 99.9% of the total liquid contamination is water.
  6. Oil vapour. Like water, oil vapour cools and condensates once inside the system.
  7. Liquid oil. Most compressors use oil in the compression stage for sealing, lubrication and cooling. This can get carried over into the compressed air system as liquid oil and aerosols.
  8. Oil aerosol
  9. Rust scale. Scale can get built up in the air receivers and pipework of ‘wet’ systems. It can break away to cause damage or blockages.
  10. Pipe scale

It’s difficult to avoid many of these sources of contamination. With the correct filtration, it’s easy to remove contaminants from your compressed air system.

Selecting filtration

When selecting filtration, it is important to consider the following factors:

  • Sizing. You must use a filter which can handle the compressed air flow rate at the minimum system pressure and the maximum temperature.
  • Grade of filtration. A single filter isn’t designed to be able to treat all contaminants. You may need to use a combination of different grades and methods throughout the system.
  • Application. There are strict air purity standards in place for certain industries, such as food and pharmaceuticals.
  • Cost. The cost to operate and maintain a filter may vary, especially between premium and budget brands. Consider the total cost of ownership rather than the initial sale price.

Filtration types

Water separators

Water separators reduce the content of all liquids at the point of installation. They are often the first piece of equipment installed downstream of an aftercooler or air receiver. They protect coalescing filters from liquid contamination. They are not always necessary if no condensation occurs before the filters.

Coalescing filters

Coalescing filters work against many contaminants, including atmospheric, rust, scale, microorganisms and aerosols. They protect refrigeration and desiccant dryers from contamination. They are usually installed near to the compressor. For best practice install them in pairs, one general purpose and one high efficiency, to extend the life of both elements.

Oil vapour removal filters

Oil vapour doesn’t get removed by any of the previous filters. Vapour removal filters use an absorption process, using activated carbon, carbon cloth or paper to capture and remove contaminants. They are usually matched to pipe size. They need frequent element changes to achieve the required air quality. This filter is best suited for point of use applications.

Dry particulate filters

Dry particulate filters remove desiccant particles following an absorption dryer. They act like a coalescing filter, capturing and holding particles.

Sterile air filters

For critical applications needing 100% particulate removal, sterile air filters can be used. They are designed so they can be sterilised in place by steam

Understanding the requirements of your compressed air system is vital to selecting the correct filter. Don’t rely on guesswork as the quality of your system and final product could get compromised. To get guaranteed dry air, compressed air dryers play an important role.