Compressed Air Oil And Water Separators Explained

Compressed air will inevitably create moisture that needs to come out so it doesn’t cause malfunctions in the equipment. When the air is compressed and the moisture in the air condenses, it will bring along some oil and lubricants that keep the compressor running smoothly. This oil and water mix can’t simply be disposed of down the drain or be poured onto the ground. 

Compressed air oil and water separators do just what it sounds like. These are pieces of equipment added to a compressor, to properly separate the condensed water and oils so they both can be properly disposed of. Most industrial applications can benefit from the use of a compressed air oil and water separator.

This article will explain what a compressed air oil-water separator is, how they work, and where these pieces of equipment may be needed. 

What is an Air Compressor Oil and Water Separator Exactly?

When an air compressor oil water separator is installed, it takes that mixed condensate and separates the oil and lubricant particles from the water. The water is then clean enough to dispose of in a sanitary sewer drain. The leftover oils can then be disposed of properly. 

Unless the air is dried completely before entering an air compressor, condensate is going to form inside the compressed air tank.

This happens because the moisture particles in the air get compressed down so much that the air becomes saturated with moisture. The water molecules then combine and form a condensate. 

As air is moved through the compressor, it also picks up minute quantities of oils and lubricants essential for proper air compressor function. While some of this oil and water mixture can go out when the compressed air is used, most of it stays behind in the tank until it’s purged. 

This oil and water mix can’t simply be washed down a drain or poured onto the ground. Since the introduction of the EPA’s Clean Water Act, some regulations need to be followed when disposing of harmful chemicals like oils and lubricants. 

How Does a Compressed Air Oil Water Separator Work?

An oil water separator can be added aftermarket to the compressor in order to save the company money because there won’t be a need to store heavy containers full of contaminated water.

This also helps to save the environment because one gallon of oil can end up contaminating up to 1 million gallons of groundwater. 

The oil-contaminated water is collected from every compressor and component that creates condensate. Each compressor and part that makes the condensed water will need to be piped to the oil and water separator where it can be filtered. 

First Stage Filtration

These oil and water separators work by going through a few filtration stages. The first stage uses the properties of how oil floats on top of the water because of the density differences. A pre-filter made of polypropylene fibers sits on the upper surface of the water and absorbs many of the floating oil particles.

Polypropylene is a material that is considered oleophilic while also being hydrophobic. This means it attracts oil molecules, while simultaneously repelling water molecules. 

As the first stage filter collects more and more oil from the water, it will eventually sink due to all the oil attached to it. When that happens, the filter needs to be replaced. 

Second and Third Stage Filters

Once the bulk of the oil has been removed from the condensate water, it’s still not clean enough to dispose of in a drain or the soil. There are often second or third-stage filters. These filters contain activated carbon or other materials that further remove oil from the water. 

Activated carbon is an oil adsorbent material. A material that is adsorbent collects molecules on the surface instead of absorbing them into itself. Activated carbon has millions of tiny pores which increase the surface area, allowing more molecules of oil to be attracted to the filter. 

The water moves slowly through the activated carbon filters where the oil gets trapped in all the tiny pores, but the water drips through without getting absorbed. Using activated carbon filters helps to get the water oil mixture down to nearly 10 PPM (parts per million) which is lower than the EPA standards. 

This filtered water is usually clean enough to drain into the local sewer or down into the drain. Just test the water first to find out what level of contaminants are present after filtration. 

The Clean Water Act states that water drained into municipal wastewater systems must contain less than 40 PPM of oil. Some state and county authorities may have even stricter regulations when it comes to draining water. Contact the local water treatment facilities to find out for sure.  

Do You Need an Oil Water Separator for Your Air Compressor?

Most, if not all air compressors should have an oil water separator, especially in a shop or industrial setting. The condensate from air compressors can contain much higher levels of oil than is allowed by the EPA and the Clean Water Act. 

This byproduct needs to be disposed of correctly to avoid stiff penalties and fines. This can be accomplished by storing the wastewater in large drums, then holding them in a storage area or facility. Eventually, the waste will need to be disposed of properly. 

Proper disposal of oil-contaminated water means contacting an expensive company to come haul away the heavy barrels so they can filter them out and dispose of them. This process can get expensive, especially if the company charges by weight. 

In a relatively short time, the extra cost of adding on an oil water separator will pay for itself compared to paying a company to dispose of the contaminated condensate. With the EPA cracking down on companies that use compressors, an oil water separator will be in compliance with the Clean Water Act and be safe from fines. 

oes an Oil Water Separator Require Excessive Maintenance?

Once the oil and water separator is installed, most often the only maintenance that will be required is water testing and regular filter changes. Ensure the machine is installed where all the filters can easily be accessed. It will make for a more seamless maintenance application. 

Depending on how often the compressors are used as well as the humidity and temperature of the environment around the compressors will have a profound effect on how much condensate is created. These factors also determine how much maintenance will need to be performed. 

A very humid and hot environment will create a lot of condensation in a short amount of time compared to dry, cool conditions. Of course, if the facility is cooled and/or the air is dried before entering the compressors, there will be much less condensation accumulation.

Weekly or Monthly

About once a month for low to moderate usage the filtered water needs to be checked. If the compressors are being used daily or for extended periods very frequently, then the water needs to be checked weekly. This is to make sure the filters are working properly and the water is meeting the correct standards. 

Monthly or Quarterly Maintenance

Either monthly or quarterly, open up the tanks to inspect the inside. Even with the polypropylene filters taking much of the oil from the surface of the water, an oily sludge can appear on top of the water inside the storage tank. To take care of this jelly-like substance, skim it off with a fine mesh skimmer or suction it off.

Quarterly to Yearly Maintenance

Replace the filters every year at the very least to keep everything running smoothly and to make sure the condensate water is reaching the lowest level of contaminants possible. If the compressors are seeing heavy usage, then the filters may need to be replaced sooner than annually. 

Testing the water that comes out of the oil water separator on a regular basis will also indicate when the filters need to be replaced. When the filters need to be changed, whether it’s the polypropylene filters or the activated carbon filters, simply pull them out of the tank and seal them in a plastic bag or container. 

The oil will continue to cling to the filters. Simply seal them in an airtight container and dispose of them according to proper environmental practices.

Disposing of a few filters soaked in oil and lubricants is much easier than disposing of hundreds of gallons of contaminated water. It’s also much more economical, so a compressed air oil water filter is a good investment. 


Compressed air can create a lot of water with dangerous levels of oil and lubricants mixed in. In order to help the environment and reduce the cost of storing, packing, and hauling away hazardous chemicals, a compressed air oil water separator can save a lot of money. 

It also keeps air compressors and their byproducts in compliance with the EPA and the Clean Water Act. No one wants to be hit with fines or get in trouble for simply trying to work. Get a compressed air oil and water separator to make things go smoother when using air compressors. 

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