To make it easier to compare air quality between systems and to rate equipment like filters and dryers, an ISO standard is produced, to classify the compressed air quality.
Class 0 is the highest quality, super-clean air.
|CLASS||SOLID / DIRT Particle size in micron||WATER @ 7 bar / 100 psiPressure Dewpoint||OIL (including vapor)|
|Max number of particles per m3||° C||° F||Mg /m3||PPM|
|0||As specified||As specified||As specified|
|Leakages in air, oil or fuel system||check||check||check|
|Coolers ( engine, compressor oil and air)||Clean||Clean|
|Min and max rpm engine||check||check||Check|
|Torque wheel nuts||check||check||Check|
|Safety valve (air receiver)||Test|
|Towbar and system||grease||grease|
|Oil separator||Check pressure drop||Replace separator|
|Tension of V-belts||Adjust||Adjust|
|Oil filter compressor||Change|
|Air intake filter||Change|
|Safety cartridge air intake filter (if installed)||Change|
|Oil filter engine||Change||Change|
|Intake and exhaust valves engine||Adjust|
|Compressed air after filters (if installed)||Change|
How to use the table
The ISO standard gives quality ratings for solid particles, for water and for oil. To completely ‘belong' to a class, all requirements must be met (solids, water and oil).
For example, air with 2.000 particles of 2.0 um and a pressure dewpoint of -20 degrees Celsius will be class 5.
2.000 particles of 2.0 um will give us class 5 for solid particles/dirt. -20 degrees Celsius will give us class 3 for water. The overall class of the compressed air will be 5, although for water only it will be higher: class 3.
Again, use your commons sense.
You might not be interested in oil in your air, but dust and water might be disastrous for your equipment.
Here's a small list of general recommendations for air quality classes for different kinds of equipment / use.
Air tools with air motors (like grinders):
Other hand tools:
Machines with pneumatic cylinders:
General workshop air: