The ISO 8573-1 guidance specifies purity classes of compressed air with respect to particles, water and oil, independent of the location in the compressed air system at which the air is specified or measured.
This part of ISO 8573 provides general information about contaminants in compressed air systems as well as links to the other parts of ISO 8573, either for the measurement of compressed air purity or the specification of compressed air purity requirements.
The three major contaminants in compressed air are solid particles, water and oil; these are categorized by compressed air purity classes.
These compressed air purity classes group the concentrations of each of the above contaminants into ranges, each range being given its own purity class index. The range limits are aligned to those figures found in practice.
Compressed Air Purity Classes for Particles
The particle purity classes are identified and defined in below Table. Measurements shall be made in accordance with ISO 8573-4 and, when required, ISO 8573-8.
Where it is determined that there are particles with a size greater than 5 µm, then the classification of 1 to 5 cannot be applied.
A.3.2.2 Particle Classes 6 and 7
Industrial tools and pneumatic-fluid power-operated machines have traditionally been supplied with air filtered by general-purpose filters with a notional particle size rating of 5 µm (class 6) and 40 µm (class 7). These ratings were applied many years ago before the latest particle-size-measuring systems were developed and have given satisfactory service while keeping the pressure losses (and therefore the power losses) to a minimum.
Compressed Air Purity Classes for Humidity and Liquid Water
The humidity and liquid water purity classes are identified and defined in below Table. Measurements shall be made in accordance with ISO 8573-3 and, when required, ISO 8573-9.
Compressed Air Purity Classes for Total Oil
The total oil purity classes are identified and defined in below Table. Measurements for liquid oil and aerosols of oil shall be made in accordance with ISO 8573-2. It is considered that, for classes 3, 4 and X, the oil vapour content is not expected to significantly affect the total concentration; therefore, the measurement of vapour is optional. Where it is deemed necessary to measure the oil vapour, then ISO 8573-5 shall be used.
Clause 4. Reference conditions
The reference conditions for gas volumes shall be as follows:
⎯ air temperature: 20 °C
⎯ absolute air pressure: 100 kPa = [1 bar ](a)
⎯ relative water vapour pressure: 0