Importance of the Compressed Air Quality

Estimated time to read: 7 mins

It is of utmost importance to the user that the compressed air quality be accurate. Atmospheric air that is sucked into a compressor always contains moisture, dust and oil aerosols. The amount and ratio of these contaminants depend on the season, weather and where the compressor is. It is crucial to dispose of these contaminants as soon as possible to avoid deterioration of pipes and other pneumatic devices in your system. 

Why is it important to consider the air quality?

Compressed air can contain unwanted substances, such as water in drop or vapor form, oil in drop or aerosol form, and dust.

Filtry a cyklónové separátory pro úpravu stlačeného vzduchu
Depending on the compressed air's application area, these substances can impair production results and even increase costs. Air treatment aims to produce the compressed air quality specified by the consumer. When the role of compressed air in a process is clearly defined, finding the system that will be the most profitable and efficient in that specific situation is simple. This will be determined by your finished product and the working environment of your application. Does your product come into direct contact with compressed air, or will oil vapour harm the working environment? These and many other different conditions are factors to consider. You may require a systematic method to be used, in order to determine your ideal equipment choice.

What are the different air purity classes?

International Standard ISO 85731 "Compressed air for general use", determines the extent to which compressed air needs to be cleaned (see table below). It defines which other devices can be used to achieve the required compressed air quality class.

Quality class

Solid particle content Water content Oil content

Max. size


Max. amount


Dew point




Max. amount


1 0.1 0.1 -70 0.003 0.01
2 1 1 -40 0.11 0.1
3 5 5 -20 0.88 1.0
4 40 10 +3 6.0 5
5 - - +7 7.8 25
6 - - +10 9.4 -

How do I remove condensation from the compressor?

Moisture or condensation should be removed from your compressor as quickly and efficiently as possible to prevent damage to your compressed air system. A Compressed air dryer is the best machinery to do this conveniently and optimally. They remove the moisture from compressed air and thereby protect downstream equipment from corrosion, and your final products from contamination. This leads to more savings over time and a reduced maintenance cost for your machinery.  

Our ALUP AVSD Dryer makes this technology more reliable and optimal by allowing for variable speed, as opposed to just one full power setting from less efficient dryers on the market. This version also enables a lower cost of ownership and more sustainability in your operation, making it the gold standard for compressed air dryers. 

How do filters help?

A filter separates the air particles from contaminant particles. The particle-separating capacity of a filter is a result of the combined sub-capacities (for the different particle sizes) as set forth above. In reality, each filter is a compromise, as no filter is efficient across the entire particle size range. Even the effect of the stream velocity on the separating capacity for different particle sizes is not a decisive factor.

Generally, particles between 0.1μm and 0.2μm are the most difficult to separate (Most Penetrating Particle Size).2.35.png As stated above, the total capturing efficiency of a coalescence filter can be attributed to a combination of all occurring mechanisms. The importance of each mechanism, the particle sizes for which they occur and the value of the total efficiency heavily depend on the particle size distribution of the aerosol, the airspeed and the fiber diameter distribution of the filter media. 

Oil and water in aerosol form behave similar to other particles and can also be separated using a coalescing filter. In the filter, these liquid aerosols coalesce into larger droplets that sink to the bottom of the filter due to gravitational forces. The filter can separate oil in aerosol as well as in liquid form. However, due to the inherent high concentration, oil in liquid form will result in high pressure drop and oil carry-over. If the oil in the vapor form is to be separated, the filter must contain a suitable adsorption material, usually activated carbon.

All filtering inevitably results in a pressure drop, and energy loss in the compressed air system. Finer filters with a tighter structure cause a higher pressure drop and may get clogged more quickly, demanding more frequent filter replacement and higher maintenance costs. The air quality in regards to the amount of particles and the presence of water and oil is defined in ISO 8573-1, the industry standard for air purity. In order to eliminate the risk of air contamination in a critical process, it is recommended that only compressed air classified as Class 0 be used. Additionally, filters must be dimensioned so that they handle the nominal flow properly and have a larger capacity threshold to manage some pressure drop due to a certain amount of blockage.

How do air dryers help?

Condensing or adsorption dryers are used to remove moisture from compressed air. Condensing dryers are used when the maximum air quality required is class 4, meaning the dew point is less than 3°C. If compressed air with less moisture (a lower pressure dew point) is required, an adsorption dryer must be installed.

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