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Oil-free vs Oil-injected Air Compressors: Class 0 Explained
Oct
Compressed air is used in almost every factory, but not every process can tolerate even a trace of oil. In food, pharma and electronics, a few droplets can ruin a whole batch. This guide explains how oil-free and oil-injected compressors differ, what ISO 8573-1 Class 0 means and how to choose.
How do they differ?
In an oil-free compressor no lubricating oil enters the compression chamber. The screw or tooth rotors are synchronised by timing gears and never touch, so no oil is needed to seal or cool the chamber. Oil only lubricates gears and bearings and is fully isolated from the air stream.
An oil-injected screw compressor injects oil into the chamber to seal, cool and lubricate, then separates it from the air. Even with good separation, a small amount of oil vapour and aerosol remains, so extra filtration is needed for sensitive uses.
What is ISO 8573-1 Class 0?
ISO 8573-1 classifies compressed air by particles, water and oil. Class 0 is the strictest: limits are specified by the user or supplier and must be tighter than Class 1. Atlas Copco ZR/ZT oil-free compressors are certified to ISO 8573-1 Class 0 (2010), meaning no oil contamination risk from the compressor itself.
| ISO 8573-1 class | Max. total oil (mg/m³) | Max. pressure dew point |
|---|---|---|
| Class 0 | As specified by user or supplier, stricter than Class 1 | As specified |
| Class 1 | 0.01 | -70°C |
| Class 2 | 0.1 | -40°C |
| Class 3 | 1 | -20°C |
| Class 4 | 5 | +3°C |
| Class 5 | – | +7°C |
| Class 6 | – | +10°C |
Comparison
| Criteria | Oil-free (ZR/ZT) | Oil-injected (GA) |
|---|---|---|
| Air quality | Class 0, no oil in the chamber | Residual oil, extra filters needed |
| Investment | Higher | Lower |
| Filtration and condensate | Oil-free condensate, fewer filters | Carbon filters, oil-water separation |
| Product risk | Practically zero | Depends on filtration and maintenance |
| Typical use | Food, pharma, electronics, textiles, paint | Metalworking, plastics, wood, general industry |
Which industries need oil-free air?
- Food, beverage and dairy
- Pharmaceuticals and healthcare
- Electronics and semiconductors
- Textiles (air-jet looms)
- Automotive paint shops and chemicals
Choosing an oil-free range
| Air demand | Suggested range |
|---|---|
| 24 – 142 l/s (15 – 55 kW) | Atlas Copco ZT 15–22, ZR/ZT 30–55 VSD |
| 78 – 452 l/s, variable demand | ZR/ZT 75–160 VSD+ |
| 266 – 774 l/s, stable base load | ZR/ZT 110–275 |
| 127 – 830 l/s, variable demand | ZR/ZT 132–315 VSD |
| 695 – 2046 l/s, large plants | ZR 300–750 or ZR 400–900 VSD |
ZT units are air-cooled; ZR units are water-cooled, quieter and well suited to energy recovery. Full Feature (FF) versions include an integrated dryer.
Keep in mind
- Oil-free air still contains water vapour and particles from the intake, so a dryer and particle filters are still needed.
- If only a few points need clean air, an oil-injected unit with point-of-use filters may work; for air in direct product contact, oil-free is the safer long-term choice.
Get sizing advice and a quote
FEYANA supplies Atlas Copco oil-injected screw compressors, Class 0 oil-free compressors and compressed air dryers from Vietnam to Singapore, Malaysia, Thailand, Indonesia, the Philippines and beyond. Send your required flow, working pressure, air quality class and site conditions via WhatsApp +84 988 641 591 or sales.00@feyana.com. Browse all air compressors and dryers.
