Why Do I Need an Oil-Water Separator and How Does It Work? 

Inside of your air compressor, you will find an internal oil-water separator. The internal separator separates the water from the oil that stays inside the compressor. This is the oil that is used to lube the rotary screw and other internal parts. In addition to this internal component, you will also want to use an external oil-water separator.

During the compression process, outside contaminants such as water vapor and dust are mixed in with the hot oil. Once the air has cooled down at the end of the compression process, contaminated condensate is generated. If this moisture collects anywhere in the distribution system (mainly air receivers, filter bowls or moisture separators), the condensate will get into the compressed air system and cause damage to the equipment and ruin the final product. Because of this unavoidable, expensive and ugly by-product of using compressed air, an oil-water separator is necessary and beneficial to any compressed air operation. But how exactly does an oil-water separator work?

Chicago Pneumatic's Oil-Water Separator Series (OWS) allows you to minimize your compressed air waste treatment costs, while also being eco-friendly. These separator’s use a patented multi-state filtration process that separates contaminants from condensate. The contaminants are trapped in the 1st stage filter and polished in the 2nd stage tower, leaving only the clean water to be drained.

Here is the step-by-step process on how the OWS filters work:

1. Collection of untreated condensate enters the system.

2. Condensates are collected though mufflers located in the integral expansion chamber where first stage separation takes place by depressurization.

3. The depressurized condensate then flows into column A and passes through an oleophilic media, made of oil absorbing fibers which allow water to pass through.

4. The oleophilic filter floats in column A.

5. This is advantageous for absorbing residual oil floating on the surface.

6. The additional weight of the oil causes the filter to gradually sink as it gets more saturated, which ensures that clean filter material is always in contact with the surface of the water.

7. The indicator stick at the top of column A shows the status of the filter, as the filter is consumed the stick sinks. The filter has to be changed just before its fully submerged.

8. The prefiltered condensate is then directed into column B.

9. Column B contains activated carbon, and absorbs the remaining oil in the condensate. The large capacity of the system prevents any risk of spillage in case of blockage of the system or if the system produces excessive quantities of condensate.

10. Clean water exits the disposable filter through the outlet port and is discharged from the OWS purifier. Oil content is approximately 4 mg/gal, at reference conditions, at the outlet, a level that allows disposal of the condensate without risk to the environment.




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Ash Air has been around in New Zealand since 1979, and we’ve grown into a nationwide company with international support and a reputation for quality and reliability.We look after all things compressed air for your business!

  • Reciprocating, Screw, air compressors
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  • An extensive line of air treatment components

Ash Air's range of Chicago Pneumatic, Alup, Pneumatech, and Quincy compressors are used extensively around the world in industries ranging from oil and gas to food, automotive and farming, and we bring you these world class compressors here in the land of the long white cloud.Our technicians are compressed air equipment experts and are dedicated to addressing customer needs. Supported by a 13 locations nationwide, Ash Air offers one of the widest selections of compressed air equipment and parts available today in New Zealand.

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  • Increasing uptime
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