Humidity (Water) Classes
Water in compressed air causes corrosion, bacterial growth, and process problems. ISO 8573-1 defines 10 classes (0-9) based on pressure dew point or liquid water content.
Classification Table
| Class | Pressure Dew Point | Liquid water |
|---|---|---|
| 0 | Per user specification | - |
| 1 | ≤ -94°F (-70°C) | - |
| 2 | ≤ -40°F (-40°C) | - |
| 3 | ≤ -4°F (-20°C) | - |
| 4 | ≤ +37°F (+3°C) | - |
| 5 | ≤ +45°F (+7°C) | - |
| 6 | ≤ +50°F (+10°C) | - |
| 7 | - | ≤ 0.5 g/m³ |
| 8 | - | ≤ 5 g/m³ |
| 9 | - | ≤ 10 g/m³ |
Important difference
Classes 1-6 specify dew point (no liquid water). Classes 7-9 allow liquid water at specific concentrations.
Interpretation
- Class 1: Extremely dry air, for cold climates or critical processes
- Class 2: Very dry air, typical for electronics and pharmaceutical
- Classes 3-4: Dry air, suitable for most industrial applications
- Classes 5-6: Basic drying with refrigerated dryers
- Classes 7-9: Allow liquid water presence
Dryer Selection
- Classes 1-3: Require desiccant dryer
- Classes 4-6: Refrigerated dryer is sufficient
- Classes 7-9: No dryer or just condensate separator