Water is a natural byproduct of air compression. When air is compressed, moisture condenses out—and there will always be water in compressed air unless we actively remove it.
When you're seeing water in your air lines, tools, or equipment, the drying or drainage system isn't working properly. This could be a failed automatic drain, a dryer that's not reaching proper dewpoint, or simply no drying equipment installed for the application.
Rotary Screw Troubleshooting
Water in Air Lines – Rotary Screw Air Compressor Troubleshooting
Moisture contaminating compressed air and downstream equipment—usually a dryer, drain, or condensate management problem.
Industrial systems
Field-tested diagnostics
Independent & unbiased
Safety Notice
Water in compressed air causes rust in tools and equipment, damages pneumatic controls, contaminates products, and accelerates wear in cylinders and valves. For painting, blasting, or food applications, moisture is a critical quality issue.
What this problem usually means
Check these first
5–10 minute checks before diving deeper
- Check automatic condensate drain operation—is water being discharged regularly (every few minutes)?
- Open the manual drain valve—if lots of water comes out, the auto drain isn't working
- If you have a dryer, check the dewpoint reading—should be below the coldest point in your piping
- Verify dryer is running and cycling properly (refrigerated) or regenerating (desiccant)
- Check for dryer bypass valves—is air bypassing the dryer?
- Inspect aftercooler operation—is it cooling the air enough for moisture to drop out?
- Check ambient conditions—high humidity days produce more condensate
- Look at the receiver tank drain—water accumulation indicates drainage issues upstream
Common root causes
Why this happens in rotary screw compressors
Automatic drain not working
Float drains can stick, timer drains can fail, zero-loss drains can clog. If condensate isn't being discharged, it ends up in the air lines.
Dryer not achieving dewpoint
Refrigerated dryer not cooling properly, desiccant dryer not regenerating, or dryer undersized for the load. Check dewpoint reading.
No dryer installed
Some applications need dry air but have no dryer. Aftercooler and drains alone won't provide dry air for moisture-sensitive applications.
Dryer bypassed
Bypass valve left open during maintenance or to meet demand. All air must go through the dryer for proper drying.
Aftercooler not working
If aftercooler doesn't cool the air before the dryer, too much moisture enters the dryer, overwhelming its capacity.
What NOT to do
Don't just add more filters and hope for the best. Coalescing filters remove liquid water and oil, but they don't dry the air. If the dewpoint is too high, moisture will condense in the piping downstream of any filter. Fix the source: drains and dryers.
Full Rotary Screw Troubleshooting Manual
Step-by-step diagnostics, root cause logic, and practical fixes for oil-injected rotary screw compressors. Save time and reduce downtime with proven methods.
- Step-by-step diagnostics for common failures
- Root cause analysis techniques
- Practical fixes with parts notes
- Works across all major brands