A micrometre rating is not a purity class
A filter rating in µm must be accompanied by a definition of efficiency and test conditions. It does not automatically mean that everything larger is always removed and nothing smaller passes through. ISO classes apply to the resulting air, not merely to the nominal designation of the element.
Measure what classification requires
Number-based classes require the appropriate size bands. A missing band cannot be treated as a zero count. Classes 1–5 also require particles larger than 5 µm to be excluded. Mass-based classes have different requirements; particle counts cannot simply be converted to mg/m³ without knowing particle properties.
What to check in practice
- Define the required class and an appropriate measurement method.
- Check the condition of pipework downstream of the final filter.
- Consider possible dust release from the adsorbent and the need for a downstream filter.
Example scenario
The instrument reports only particles above 0.5 µm. The band above 0.1 to 0.5 µm is missing for class 1 assessment. Even zero counts in the larger bands are therefore insufficient to confirm the complete particle class 1.
What to watch out for
- Treating missing data as zero.
- Calculating the class from just one size band.
- Overlooking rust and wear debris generated downstream of air treatment.
Will a point-of-use filter at the machine help?
It can capture contaminants coming from the pipework if correctly selected and maintained. It does not remove the cause of corrosion, however, and may not address water or oil vapour. Its benefit must be assessed against the specific problem.