Stage 1
Diffusion and Depressurization
Condensate enters the separator through one or more inlets. A diffuser reduces pressure and helps remove larger solid particles.
Compressor Condensate Treatment Guide
How Oil-Water Separators Work
Oil-water separators treat condensate produced by oil-lubricated compressed air systems. They separate compressor oil from water so the collected liquid can be handled more responsibly and in accordance with applicable requirements.
This guide explains the filtration stages, separator media, sizing, maintenance and differences between Atlas Copco OSC and Quincy QOCS systems.
Oil-Water Separator Topics
Quick Answer: What Does an Oil-Water Separator Do?
An oil-water separator removes compressor lubricant from oily condensate before the water is discharged or otherwise handled.
The condensate passes through multiple stages that separate solids, free oil and fine oil droplets. Polypropylene media, activated carbon or organoclay are commonly used depending on the separator design and oil emulsion.
Atlas Copco OSC literature describes multi-stage filtration with outlet oil content as low as approximately 5 to 10 ppm depending on configuration, while Quincy QOCS literature describes approximately 5 ppm performance with multi-stage filtration.
What Is Compressor Condensate?
Compressed air contains water vapor. As hot compressed air cools, that vapor condenses into liquid water. In an oil-lubricated compressor, the liquid can also contain compressor lubricant and other contaminants.
Humid Air Enters Compressor
Air Is Compressed and Heated
Air Cools
Water Condenses
Oil Mixes With Condensate
Separator Treats the Liquid
How Multi-Stage Oil-Water Separation Works
Stage 2
Polypropylene Oil Capture
The liquid passes through polypropylene media that adsorbs free oil while allowing water to continue through the system.
Stage 3
Natural Separation
Remaining free oil can float to the top of the chamber and be captured by the filter bag or media.
Stage 4
Fine Oil Removal
Activated carbon or organoclay cartridges capture smaller oil droplets and stronger emulsions.
Stage 5
Outlet Verification
Some separators include test outlets or indicators to help verify filtration performance and service condition.
Stage 6
Treated Water Discharge
Treated condensate exits with greatly reduced residual oil content, subject to the separator design and applicable discharge requirements.
Oil-Water Separator Media
Primary Stage
Polypropylene
Captures larger oil droplets while allowing water to pass through.
Polishing Stage
Activated Carbon
Removes smaller residual oil droplets and helps reduce outlet oil content.
Strong Emulsions
Organoclay
Used where stronger oil-water emulsions require more aggressive adsorption performance.
Oil-Water Separator Selector
Use this tool for a preliminary capacity range and product-family recommendation.
Preliminary Separator Recommendation
Adjusted planning capacity—
Suggested family—
Service priority—
Important: Final sizing must use the manufacturer's published capacity tables and correction factors for climate, operating hours, oil type, compressor lubricant and connected treatment equipment.
Atlas Copco OSC vs. Quincy QOCS
Oil-Water Separator Product Family Comparison
| Feature | Atlas Copco OSC | Quincy QOCS |
|---|---|---|
| Filtration Design | Multi-stage polypropylene plus activated carbon or organoclay depending on configuration | Multi-stage polypropylene plus organoclay cartridge |
| Published Outlet Oil | Approximately 10 ppm, with 5 ppm configurations available | Approximately 5 ppm |
| Service Interval | Up to approximately 4,000 hours in published literature | Approximately 4,000-hour filter life in published literature |
| Indicators | Service and overflow indicators on supported models | Dual service indicators on supported models |
| Capacity Range | Broad range from small systems to multi-thousand-CFM systems | Published range from 25 CFM to 2,650 CFM |
| Best Selection Method | Match total compressor capacity, operating hours, climate, lubricant and connected dryers/filters. | |
Oil-Water Separator Maintenance
Inspect
Check Flow and Indicators
Confirm condensate is entering and leaving normally and that service or overflow indicators are not showing a problem.
Test
Verify Outlet Condition
Use the test outlet or approved verification method where provided.
Replace
Change Saturated Media
Replace filter bags and cartridges according to service indicators, hours and outlet performance.
Protect
Prevent Freezing
Install and operate the separator within its environmental limits and protect it from freezing where necessary.
Shop Oil-Water Separators
All Brands
All Oil-Water Separators
Atlas Copco
Atlas Copco Separators
Quincy
Quincy Separators
QOCS 25
Compact Quincy condensate purifier for supported small systems.
QOCS 106
Quincy condensate purifier for larger supported compressor systems.
OSC 300 Clay
Atlas Copco OSC clay separator product for supported applications.
Need Help Sizing a Separator?
Provide total compressor CFM, lubricant type, operating hours, climate and whether filters and dryers discharge into the separator.
Related Air Treatment Resources
Oil-Water Separator FAQs
Can compressor condensate be poured down a drain?
Oily condensate may require treatment before discharge. Follow applicable local requirements and facility procedures.
Do oil-water separators remove all oil?
They greatly reduce residual oil, but performance depends on the separator design, media condition, oil type and operating conditions.
How often should separator media be replaced?
Replace media according to service indicators, operating hours, outlet performance and the manufacturer schedule. Published OSC and QOCS literature references approximately 4,000-hour intervals under stated conditions.
Can one separator handle multiple compressors?
Yes, if it is sized for the combined compressor capacity and all connected condensate sources.
Do dryers and filters affect separator sizing?
Yes. Condensate from dryers and filters can increase the total liquid load and is included in some published sizing tables.
What is organoclay used for?
Organoclay is used to capture stronger oil-water emulsions that may be difficult for standard carbon media to treat.
What happens when separator media is saturated?
Outlet oil content can rise, flow may be restricted and untreated condensate may bypass effective filtration.
Can an oil-water separator freeze?
Yes. Water-containing equipment can freeze if installed below its environmental rating. Protect the separator and drain lines from freezing.
Is a water separator the same as an oil-water separator?
No. A water separator removes liquid water from compressed air. An oil-water separator treats collected compressor condensate.
What information is needed to size a separator?
Total compressor CFM, operating hours, climate, lubricant type and whether dryers and filters discharge into the separator.