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Compressed Air Quality Classes | Air Compressor Guide
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Compressed Air Quality Classes

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