oil water separator

Why You Need an Oil Water Separator

Why You Need an Oil Water Separator

Oil is a known enemy, whether it be to your clothing, wallet, or the environment. Oil spills can cause catastrophic problems, which can have long-lasting effects on the life in that area. It should not need to be said, but any industry that uses oil and does not have proper disposal needs to change that. 

It may seem like there is a choice whether to filter your oil, but that idea is a façade. Every viable option involves filtering or properly disposing of the oil. The only thing not filtering does for you is guarantee you will be hit with a hefty fine whenever you are caught. You will need a specific piece of equipment if you use oil in your compressor, and no, there isn’t any workaround.

The equipment you will need is an oil water separator, which does exactly as the name suggests. Water is a major byproduct of compressing air, and while under immense pressure, this water can mix with oil and make removing that oil tricky. Now you might be wondering how this occurs because typically, oil rises above water due to being lighter.

You are right that oil is lighter than water; oil water separators use that principle to remove the oil after it has separated from the water. The problem occurs due to the immense pressure compressed air is kept under. Particles under immense pressure don’t have much wiggle room, which can cause substances that are similar to combine, like oil and water. The pressure must then be released so the two can separate into individual layers again.

Stokes’ Law is the governing principle for oil water separators and how they can successfully remove oil from the condensate. George Stokes, the English mathematician, was responsible for discovering the relationship between solid particles and liquid. He determined the velocity at which these particles will rise or settle in a liquid. This law applies to liquids of different weights that exist in the same space.

When Stokes was doing his calculations, he made three key assumptions:

  • Particles are the same size
  • Particles are spheres
  • There is a laminar flow
    • This means the flow is gentle and smooth with no additional turbulence

Stokes Law is an extremely important factor in understanding and determining the efficiency, usage, and proper management of your system. Additional factors that can impact your system include:

  • Frequency and Intensity
  • Design Capacity
  • Emulsifying Agents
  • Maintenance Practices
  • Type of System
  • Quantity of Contaminants 


How Oil Water Separators Operate

In order to truly understand why you need an oil water separator, you would benefit from understanding how this equipment operates. Knowing the process that the wastewater and condensate must go through to be disposed of will give you an understanding of how the equipment should operate so you can take proper maintenance.

The process wastewater must go through is linear and simple if you understand the basics of compressed air. When ambient air is compressed, all the water vapor in the air is consolidated by pressure and the number of particles. This condensate will start to collect and pick up contaminants like oil and dust and carry them downstream. 

This contaminated condensate should be moving in its own dedicated piping for condensate and not in the airlines. This contaminated condensate is removed from the airlines throughout the process of compression, whether directly after compression, after the dryer, or from storage. This condensate needs to be collected so that it can be properly treated and disposed of.

After the condensate has been collected, it is transferred to the oil water separator to remove the contaminants so that the wastewater can be properly disposed of in the sewage system. For the wastewater to be able to meet quality standards for disposal.

As the condensate enters the first integral expansion, it is passed over mufflers to collect some of the initial contaminants. By using depressurization, which is an application of Stokes’ Law, the condensate can separate based on the gravitational properties of the wastewater contents. The removal of pressure allows that separation to occur and makes removing the oil easier.

After passing through the muffler, the condensate continues into “Column 1” after depressurizing it. Once it enters the column, the wastewater is passed through an oleophilic media that works similarly to a coalescing filter. The fibers of the media absorb the oil as it passes through, but it does not absorb the water. Having this filtration is the key to being able to remove the oil from the water.

This first filter rests on top of the water so that when the oil separates from it, the oil floats up into the filter to be collected. Due to this direct contact between the filter and water, the oil has nowhere to go but into the filter when it separates upward. In order to give the user an idea of where the filter is at in the absorption process, there is an indicator stick attached directly to the filter in Column 1.

As the filter becomes laden with oil, it will start to sink down but still stay on top of the water. As the filter is dropping so is that indicator stick; just before it is completely submerged is when you need to change your filter (if you can’t see yours at all you really need to switch it). Just trust the indicator to give you an indication of your filter status. 

Wastewater that has exited Column 1 will then continue on into the second column, aptly named “Column 2.”  This second column is less like a tank and more like a desiccant tower. This column is filled with activated carbon that absorbs oil as it passes through, but it still allows for the rest of the condensate to pass through cleanly. The activated carbon pulls out the oil that is remaining in the wastewater, and it brings the oil contents to around 4mg/gal.

By achieving this quantity of oil, the remaining clean water can be disposed of into the sewage system. After the final column, all left is for the remaining wastewater to be passed through a disposable filter on the discharge port. This completes the process of condensate management in the oil water separator.


What Even Needs To Be Separated

Due to the nature of compression, all of the naturally occurring particulates and moisture in the ambient air are forced together in a confined space. Alongside those naturally occurring dust and water molecules, the air also gets mixed in with the hot oil that is used as a lubricant during compression. 

While under this immense, these components combine into a single condensate that needs to be removed from the system. If this condensate is allowed to get downstream or gather in excess in components it can cause major damage to your system. This damage can be unseen as the condensate is rusting away the interior of the pipe until it bursts from the pressure.

Unfortunately, condensate is an inevitable part of the process when you are compressing air. And this condensate has to go somewhere, right? It definitely does need to be removed from the air system or else you will have much bigger problems than determining how you process your separated oil.

Technically, this oil can be disposed of two ways after it has been removed from the condensate, but the reality is that only one option makes sense. The first, and not recommended, option is the tank storage method, where you would drain all of your condensates into storage and then have to move that storage to a proper disposal site. The second option is an oil water separator, which is a bit easier.


How Does It Separate?

Similarly to many other types of equipment in the compressor industry, oil water separators have different separation methods; they all work upon similar concepts, but the techniques are different. Due to the difference in technique, varying amounts of oil can be left in your water depending on the model you choose.

There are four main types of oil separation:

  • Gravity Separation
  • Chemical Absorption
  • Non-Chemical Absorption
  • Adsorption


Gravity Separation

The simplest and easiest method of separation uses gravity as the main mechanism. This method relies upon the natural difference in weight between water and oil. Oil is lighter and floats to the top and form a separate layer from the water. This allows the oil that has separated to be skimmed off the top. This method works great except for the fact that not all of the oil will move up, some of it is still emulsified with the water.

Because some of the oil makes it through this process, the wastewater still has oil contents that are above the PPM acceptable limit. That means the contents that are separated by gravity alone are not high enough quality to meet the standards.


Chemical Absorption

When it comes to chemical separation, the media that is used is chemically attracted to oil so that it can bond with it while repelling the water. This pulls that oil out of the water and traps it in the filter media while the water continues to flow on through. 

This process ensures that the water has a low PPM of oil after separation. This allows the byproducts to be dumped into the sewage system within the necessary standards.


Non-Chemical Absorption

Unlike chemical absorption,, which has a chemical bonding process, non-chemical absorption operates using the material’s natural characteristics. The material must be oleophilic (oil-loving) while simultaneously being hydrophobic (water-fearing) so that it can attract the oil and not the water. The oil is retained in the material, and even that which has been emulsified is removed.



Adsorption and absorption are similar in name and process. With absorption, the condensate and oil are drawn into the center of the media; meanwhile, adsorption keeps the oil on the material’s surface. The oil is attracted to the surface material and the many tiny pores on them to adsorb as much oil as possible while repelling the water.


Why Should I Get One?

The biggest benefit to having an oil water separator is the improved removal of oil. Not only is it beneficial to remove oil from your system for the sake of your system, but by properly removing the oil, you are also showing environmental compliance. A properly sized oil water separator will lighten your treatment and filtration equipment load and lengthen the lifespan.

When you are able to achieve the specific oil management challenges of your particular compressed air system, you can achieve efficient oil separation and removal. By successfully doing this, you minimize the maintenance requirements for your oil water separator. This will keep your separator running smoothly and downstream treatment performing effectively.


Keeping Your Oil Water Separator Maintained

As with your compressor and other equipment, your oil water separator needs consistent and proper maintenance to reach the environmental standards while continuing to operate at peak performance. Oil water separators are mostly self-sufficient to allow longer intervals between maintenance requirements as long as it is properly sized. Sizing this equipment can be difficult because the climate can directly impact its efficiency and overall function. You should account for the estimated humidity in your area.

Proper removal and disposal of oil are beneficial to the environment but certainly can be detrimental to your wallet.  By minimizing the number of oils and particulates that make it into the oil water separator, through adequate filtration prior, lower amounts of sludge and oil will float to the top of the container to need to be removed. This will give you more time between needing maintenance on those machines.


Don’t Forget About This

The best way to ensure that your oil water separator works is to take proper care of it. There are also a few other things you’ll want to keep in mind when you are purchasing an oil water separator. First things first, an OWS should never be used to treat stormwater runoff as it is not controlled and can flood the separator.

It may not be the easiest or most rewarding thing to do when you add an oil water separator, but that’s what makes it important to do your part and get one. Just as it is the safe and responsible action to put on sunscreen or wear a bike helmet, not everyone follows the guidelines even though they should.

You might think you can get away without an oil water separator in your system, but before you commit, you may want to know some of the restrictions for not using one.

The EPA Guidelines and their fines:

  • Negligent Violations
    • A fine of $2,500 to $25,000 per day of violation and/or imprisonment up to 1 year. While a second conviction is punishable by up to $50,000 per day of violation and/or imprisonment up to 2 years.
  • Knowing Violations
    • A fine of $5,000 to $50,000 per day of violation and/or imprisonment up to 3 years. For a second conviction, violators can pay up to a $100,000 fine per day of violation and/or imprisonment for up to 6 years.
  • Knowing Endangerment
    • Knowing violations of CWA requirements that put another person in danger of imminent death or serious bodily injury can be punished by up to a $250,000 fine and/or imprisonment of up to 15 years.
  • False Statements
    • Making false material statements, representations, or certifications may be punishable by up to a $10,000 fine and/or by imprisonment of up to 2 years. If convicted of making false statements, it is punishable by up to a $20,000 fine per day of violation and/or imprisonment of up to 4 years.


Clearly, using an oil water separator is the right thing to do, and you may go unpunished for not using one or using it incorrectly, or you will get busted and face steep fines and possible imprisonment. Every time you dump unfiltered wastewater, you risk being caught and facing the consequences. 

For how little work an oil water separator is to maintain and use properly, it just doesn’t make sense not to use one. The risks of not using one far outweigh the extra work needed to run one. If you aren’t sure where to start looking for one, you’re in the right place.

Simply click here, and you will be able to shop our selection of oil water separators

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