Air Quality classes defined in ISO 8573-1

There are standardized compressed air quality classes which makes easier for manufactures to define required air quality to ensure trouble free operation of their equipment.

The ISO specify 3 major contaminants of compressed air - solid particles, water and oil. These contaminants are specified by 3 digits that are refering to purity class from table below.

Particle size and density - Definition of the size and concentration of solid matter particles like dirt or rust that may remain in the compressed air.

Pressure dew point - Definition of the temperature to which the compressed air can be cooled without condensation of the moisture it contains. The pressure dew point changes with the air pressure.

Oil content - Definition of the residual quantity of aerosols and hydrocarbons contained in the compressed air.

ClassSolid particles per m3WaterOil
0.1 - 0.5
0.5 - 1
1 - 5
Pressure dew
point in °C
Residual oil
in mg/m3
2100 000100010-400,1
3-10 00050-201

Selecting an air purity class of 2.4.1, required for our PSA systems, would specify the following air quality when operating at the standard’s reference conditions:

Class 2 Particles

In each cubic metre of compressed air, no more than 100,000 particles in the 0.1 - 0.5 micron size range are allowed.

In each cubic metre of compressed air, no more than 1,000 particles in the 0.5 - 1 micron size range is allowed.

In each cubic metre of compressed air, no more than 10 particles in the 1 - 5 micron size range is allowed.

Class 4 Water

A pressure dewpoint of +3°C or lower is required; no liquid water is allowed.

Class 1 Oil

In each cubic metre of compressed air, not more than 0.01mg of oil is allowed. This is a combined level for both oil aerosol and oil vapour.

Why is it important to meet the air quality requirements?

Besides other unwanted issues, all the contaminants deactivate the molecular sieve present in the PSA generator what makes impact on the overall performance and lifetime of the complete system.