Why Does Compressed Air Contain Water?
Ambient air contains water vapor at varying levels depending on humidity and temperature. When that air is compressed — say, to 100 PSI — the water vapor becomes significantly more concentrated relative to the air volume. As compressed air cools in your distribution piping, that concentrated moisture condenses from vapor into liquid water droplets that flow through your system along with the air.
The amount of condensate generated can be surprising. A 100 HP compressor running in humid summer conditions can produce 15–40 gallons of condensate per day. Without removal systems, that water ends up in downstream equipment, spray applications, pneumatic tools, and process piping.
What Is an Air Compressor Water Separator?
A water separator (also called a moisture separator or condensate separator) is a mechanical device installed in the compressed air distribution line that removes bulk liquid water from the airstream. It works through centrifugal action, directional changes, or impingement — forcing heavier water droplets out of the airstream so they collect in a bowl at the bottom of the separator, where they are drained either manually or automatically.
Water separators are effective at removing liquid water that has already condensed but do not remove water vapor still in the gas phase. For deeper moisture removal, they are used in combination with compressed air dryers (refrigerated or desiccant).
What Is an Oil-Water Separator for Compressed Air?
Compressed air systems using oil-lubricated compressors produce condensate that contains both water and compressor oil. This oil-contaminated condensate cannot be discharged directly to a floor drain or municipal sewer system — it must be treated before disposal to comply with environmental regulations.
An oil-water separator (OWS) is a condensate treatment device that removes the oil from the water before discharge. The treated water (with very low residual oil content, typically below 20 ppm) can then be safely disposed of via drain or sewer, while the separated oil is collected for proper disposal by a licensed waste hauler. An OWS is required for most facilities operating oil-lubricated compressors.
Types of Water Removal Equipment
- Centrifugal water separators: Use spinning action to throw water droplets to the outside wall of the separator where they drain down. Effective for bulk liquid removal at the compressor discharge or throughout distribution piping.
- Coalescing filters: Use a fine filter medium to coalesce tiny water droplets into larger ones that drain from the filter element. Remove both water droplets and oil aerosols — critical for applications requiring clean, dry air.
- Automatic condensate drains: Timer-controlled or zero-loss electronic drains that automatically discharge collected condensate from separators, dryers, and filters without wasting compressed air.
- Oil-water separators: Condensate treatment systems that use gravity separation, absorption media, or both to remove oil from compressor condensate before drain disposal.
Where to Install Water Separators in Your System
Water separators should be installed at the compressor aftercooler outlet, at the inlet to refrigerated dryers, throughout distribution piping at low points where condensate accumulates, and at any point of use where liquid water in the airstream would cause problems. A properly designed compressed air system includes moisture removal at multiple stages — not just at the compressor room.
Selecting the Right Water Separator
Key factors in water separator selection include your system's flow rate (CFM), operating pressure (PSI), the volume of condensate you need to handle, and whether oil separation is required. Brabazon's applications engineers can review your system design and recommend the appropriate separation equipment — including automatic drains and oil-water separators for compliance — for your specific installation. Call 800.825.3222 or contact us online.