To get oil-free air from your compressor, you essentially need a compressor designed to operate without oil in the compression chamber, or you need to use filtration and separation methods to remove the oil. Here's a breakdown:
Types of Compressors
There are two main types of compressors when it comes to oil:
- Oil-Lubricated Compressors: These compressors use oil to lubricate moving parts, seal compression spaces, and aid in cooling. They require oil reclamation systems to manage and separate the oil from the compressed air, but some oil can still carry over into the air stream.
- Oil-Free Compressors: These are specifically designed to compress air without using any oil in the compression chamber. This means no oil can contaminate the air directly.
How Oil-Free Compressors Work
Oil-free compressors, such as rotary screw compressors, achieve oil-free air by using specialized materials, seals, and design techniques. Here is an example of how a two-stage rotary screw compressor accomplishes this:
- Two-Stage Compression: The air is compressed in two separate stages. First stage compresses the air to around 3.5 bar g. Then the second stage compresses the air to the final discharge pressure, e.g., 7 bar g.
- Intercooling and Aftercooling: Intercooling and aftercooling stages are used in between and after the two stages of compression. These reduce the temperature of the air as it is compressed. This results in more efficient compression and reduces wear.
- No Oil in Compression Chamber: These compressors avoid using oil in the compression chamber altogether. Instead they rely on components such as water injected to provide cooling and lubrication, or non-lubricated components and special coatings to handle the stresses of compression.
Oil Reclamation
Oil-lubricated compressors require a oil reclamation system to prevent the oil from carrying over into the compressed air. These systems typically involve:
- Air/Oil Separator: This separator uses coalescing technology to separate the oil from the air stream. These are typically constructed from multiple layers of filter media designed to catch oil droplets.
- Oil Return System: The separated oil is collected and returned to the compressor's lubricating system.
Considerations for Choosing a Compressor
| Feature | Oil-Lubricated Compressors | Oil-Free Compressors |
|---|---|---|
| Air Quality | Oil carryover possible | Truly oil-free |
| Maintenance | Regular oil changes needed | Less complex maintenance |
| Cost | Usually lower initial cost | Usually higher initial cost |
| Applications | Industrial/general use | Sensitive applications |
How To Ensure Oil Free Air From An Oil Lubricated Compressor
If you have an oil-lubricated compressor, you can take steps to minimize oil carryover:
- Proper maintenance: Regularly service your compressor, including the oil separator and filters.
- Install additional filtration: Use additional in-line filters and oil coalescing filters to remove any oil that might make it through the primary separator.
- Use high-quality oil: Use the type of oil recommended by the compressor's manufacturer.
Conclusion
The most reliable way to get oil-free air is to use an oil-free compressor that has been specifically designed to produce compressed air without the use of oil. Alternatively, if you have an oil-lubricated compressor, you can achieve cleaner air by employing effective oil reclamation and additional filtration methods, but it won’t be 100% oil free.
