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Inline Filters

How to Choose an Inline Filter for Your Compressed Air System?

Picking out the right inline filter is not an art, but it can be confusing if we do not know what questions to ask or understand the process that requires filtration. Before we move further, let’s take a step back and get a general idea of filtration and why it plays an important role within the compressed air system.

Why Do You Need an Inline Filter?

Think about making a good cup of coffee in the morning, not from the “cup” machines, but from the traditional drip coffee maker. One of the most important items in making a good cup of coffee is a filter because it prevents creating a cup full of grainy particles. As insignificant as it might seem, the paper filter plays a vital role in making coffee that you can enjoy.

Even though many air compressor systems are bigger than a coffee maker, they need a filter as well. Compressed air is full of particles, aerosols and oil vapors (in oil injected pistons and screws) that contaminate the compressed air and can cause potential harm to someone using the system. Incorporating the correct inline filter can help you eliminate the unwanted particulates as well as aerosols and vapors. The number of filters and types needed will be dependent on the quality of the air your application and/or process requires. Let’s take a look at the different types of inline filters and how to choose the right one for you.

How Clean Does My Air Need to Be?

In order to understand how clean your air needs to be, you have to identify and assess the application and process that requires the compressed air. Not all applications and processes that use compressed air require the same level of filtration, which is why understanding your machine is the first step in choosing the right filter. Compressed air being used for pneumatic purposes is oftentimes supported by a standard dry particulate filter that provides filtration down to 1 or 0.01 micron. However, if your process requires an OSHA approval and elimination of oil vapors, then it is best to use a charcoal activated filter.

Contaminants within a compressed air system can originate from ambient air that enters the compressor, as well as the system (compressor) itself. There are three main contaminants that are found in compressed air: particulates, aerosols, and vapors.


  • Particulates in an air compressor are small, solid material such as dust, dirt, or pollen from the ambient air, as well as loose metal particles that are created by pipe corrosion. Depending on the sensitivity of your application and or process, contact with particles can be damaging to the end product, which can cause delays in production and quality control issues.


  • Aerosols are small droplets of liquid that are found within an air compressor system, especially in compressors using oil-injected screws. Aerosols are created from the lubricant, which in this case is the oil used in the compressor. This can be harmful to both products and people if not treated properly.


  • In the air compressor system, vapors consist of lubricants as well as any other liquid that has converted to a gas. These vapors require a special carbon activated filter to be removed from the system.

Now that we have a better understanding of the contaminants above, let’s look at what types of filtration methods are used in eliminating each type of contaminant.

Removing Dry Particulates

There are three main mechanisms that are utilized in dry particulate filters to remove solid particles of all sizes out of compressed air. These three forces contribute to the overall efficiency of the filter, so it is important to understand what each of them are.

Inertial Impaction

  • Inertial impaction occurs when particles are too heavy to flow within the compressed air stream, and as a result, get trapped in the fiber media. The larger the particles are, the easier it will be to separate them.


  • If the diameter of the particle is larger than the gap of the filter media, it will not be allowed to flow through. This process will eliminate larger particles from the airstream, leaving only small particles.


  • Diffusion happens when small particles move erratically throughout the surface, instead of following the compressed air stream. This irregular movement path is caused by the particles colliding with other gas particles, an occurrence called Brownian movement. Since the particles have a free range of motion, it is much easier and more likely that they get intercepted by the filter media and removed from the compressed air stream. Through diffusion, separation of smaller particles is easier than separating larger ones.

Removing Aerosols and Vapors

There are two types of filters used to remove aerosols and vapor. The coalescing filters are utilized to remove liquids as well as some particulates, while vapor filters use adsorption to remove vapors from compressed air.


  • Coalescing filters are used to remove aerosols and particulates, but are not effective in the removal of vapors. The coalescing process consists of bringing small droplets of liquid together in order to form large droplets. As the droplets increase in size, they fall from the filter into a moisture trap, resulting in a cleaner and dryer compressed air stream.


  • Adsorption is a chemical process that is used to remove gaseous lubricants or vapors. The process consists of bonding vapors with the surface of the media (adsorbent), which most likely uses activated charcoal in the filters due to its high surface area and attraction to the oil vapor.

As the oil vapor covers the surface of the activated charcoal over time, it is essential to change it before it is fully saturated. If not, this would lead to a breakthrough of the oil into the air system. It is also necessary to use a dust filter after the activated charcoal filter since small charcoal particles could break through and enter the airstream.

Can my Air Compressor be Damaged by Lubricants like Oil?

In order to assess the potential damage that oil can cause within your compressed air system, it is essential to understand the basic requirements for your industry or equipment that uses the compressed air. If your industry has strict health codes and/or your equipment is sensitive to oil or vapor exposure, it is crucial to use proper filtration.

Similar to particulates, lubricants can enter your air compressor system from ambient air as well as from the compressor itself. For example, facility operations that result in motor exhaust release hydrocarbons like oil aerosols into the ambient air, which can compromise air quality and lead to equipment failure. Oil injected air compressors will also release lubricants into the compressed air system, resulting in increased operational and maintenance costs. Industries such as electronics and semiconductor are especially suspect to lubricant contamination, which can result in product loss, missed deadlines and unsatisfied customers.

Poor filtration oftentimes leads to pipe corrosion, increased pressure drops, and potential equipment damage, which can result in costly downtime and unexpected repair costs. Corrosion can also cause excess debris in your piping system, which in turn will force your air compressor to work harder, leading to higher energy consumption and excess wear on compressor parts. Proper filtration is key in achieving desired results when strict codes or purity classes are enforced.

At Edmac, we understand the value of understanding what your air compressor needs, and we have an on-site product specialist staff that would love to answer any questions you may have. Give us a call at (800) 866-2959 and ask for one of our product specialists, or send us an email using the contact form.

If you know the part(s) you need, use our quick search tool at the top of the page to quickly find your part, or feel free to browse our full collection of inline filters.