Quality classes
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) | ||||
|---|---|---|---|---|---|---|---|
| 0.10<d<0.5 | 0.5<d<1.0 | 1.0<d<5.0 | |||||
| Max number of particles per m3 | ° C | ° F | Mg /m3 | PPM | |||
| 0 | As specified | As specified | As specified | ||||
| 1 | 100 | 1 | 0 | -70 | -94 | 0.01 | 0.008 |
| 2 | 100.000 | 1.000 | 10 | -40 | -40 | 0.1 | 0.08 |
| 3 | – | 10.000 | 500 | -20 | -4 | 1 | 0.8 |
| 4 | – | 1.000 | +3 | +38 | 5 | 4 | |
| 5 | – | 20.000 | +7 | +45 | 25 | 21 | |
| 6 | – | +10 | +50 | – | – | ||
| Tire pressure | check | check | Check | ||||
| 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 | ||||
| Brake system | Check/adjust | Check/adjust | Check/adjust | ||||
| Safety valve (air receiver) | Test | ||||||
| Door hinges | grease | Grease | |||||
| Towbar and system | grease | grease | |||||
| Safety switches | grease | ||||||
| Oil separator | Check pressure drop | Replace separator | |||||
| Tension of V-belts | Adjust | Adjust | |||||
| Fuel tank | Clean | Clean | |||||
| Oil compressor | Change | ||||||
| Oil filter compressor | Change | ||||||
| Air intake filter | Change | ||||||
| Safety cartridge air intake filter (if installed) | Change | ||||||
| Oil engine | Change | Change | |||||
| Oil filter engine | Change | Change | |||||
| Fuel filter | Change | ||||||
| Fuel pre-filter | 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):
Dirt: 2
Water: 5
Oil: 4
Other hand tools:
Dirt: 5
Water: 5
Oil: 4
Machines with pneumatic cylinders:
Dirt: 4
Water: 4
Oil: 4
General workshop air:
Dirt: 4
Water: 5
Oil: 4