Do You Need A Compressed Air Filter

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compressed air filters use
(Last Updated On: September 18, 2020)

If you have acquired or purchased a smaller air compressor for your home or garage workshop, chances are it did not come equipped with a compressed air filter. Do you need a compressed air filter, then? If so, why?

In the market place drive to offer the consumer the cheapest possible off-shore manufactured air compressor, not including a compressed air filter saved the compressor company a few dollars per air compressor, and allows them to keep their wholesale prices, and ultimately the consumer sell price a little lower.

Compressor air filter - www.understanding-air-compressors.com
Typical mini – in line – air compressor filter

In so doing, for most users of air compressors, they have not done you any favors.
Buy a filter here

 

How compressed air filters work

The cap in the compressed air filter directs the incoming compressed air down into the filter bowl, and against the filter bowl, which forces the air into a tight, cyclonic spiral inside the bowl.

How compressed air filters work

The compressed air, reputedly moving at nearly the speed of sound (I say reputedly as I’ve never actually measured it’s speed) literally throws free water and debris against the side to the bowl. This contaminates runs down the inside of the bowl to the bottom quiet zone, where it’s either manually or automatically drained off, depending on the type of drain in the filter bowl.

The air continues spiraling inside the bowl while it also drives through the filter element, back up to the cap, and out downstream to the application. Any debris that hasn’t been thrown out will be captured by the filter element, as long as the debris is larger than the holes in the element, the holes were measured in microns of size.

 

About Compressed Air Filters – Why Install One?

Why would you consider adding a compressed air filter to a compressor air line?

Compressed air is filthy. Your air compressor is sucking in vast quantities of ‘fresh’ air, and that air is full of grit and dust. The intake filter on your air compressor filters out much of that debris. Some always gets through.

About compressed air filters - www.understanding-air-compressors.comAs the air compressor pumps, that still-dirty air is pumped into the tank. From there, it heads out through the coupler on the compressor into your air line, and into your air tool.

Dirty compressed air acts as an abrasive, wearing inner components of your air tools, particularly of concern if you use your air tools a lot.

Depending on the element capability in the air compressor filter, as the compressed air passes through the filter element, any debris still in the air line is removed down to the filter element size, thereby reducing particulates getting to the air tool.

Let’s use coffee as an example. We all drink coffee. One of the essential items in making a cup of coffee is the use of a proper filter to avoid a cup full of grainy elements and any other leftover pieces of the coffee bean. As unimportant as it might be, the paper filter plays a crucial role in making the coffee that we all can enjoy. 

This is the same way your compressed air system requires a filter. As we have stated above, compressed air is full of particles such as grit and dust, aerosols and oil vapors (oil-injected screws and pistons) that pollute the compressed air and could cause potential harm to you.

By integrating the correct inline filter, you can eliminate the unwelcome particulates likewise vapors and aerosols. The quality of air your process or application requires will determine the number of filters and types needed. Review some questions that will guide you in choosing the correct filter.

 

1. ARO F35121-400-VS Air Line Filter, 1/4″ NPT – 150 psi Max Inlet

Product Description

  • 1/4″” NPT Port.
  • 3 Micron Filtration.
  • Polycarbonate Bowl w/ guard
  • 49 SCFM
  • 150 psig Max inlet Pressure
  • 23-125°F Temperature Range
  • Manual Drain

ARO-Flo compressed air filters are made to remove airborne liquid and solid contaminants. Filters can be ordered with various elements, which includes coalescing models which can remove oil particles and aerosols down to 0.3-Micron.


2. Dixon F17-A00M Norgren Series Manual Drain Airline Filter with Sight Glass, Metal Bowl, 1″ Size, 250 PSI, 1-1/4″ Port Size, 425 SCFM, 50 Micron

  • General-purpose with low-pressure drop and excellent water removal characteristics
  • 1qt Reservoir
  • 40 Micron element
  • 1-1/4″ Port size
  • Manual drain

3. Dixon F07-200M Norgren Series Manual Drain Miniature Filter, Transparent Bowl, 150 PSI, 1/4″ Port Size, 21 SCFM, 5 Micron

Miniature filter with transparent bowl. 1 oz. reservoir. 5-micron element. Manual drain. On hose assemblies, pressure rating is the lower of either the rating of the coupling or the hose at 70°F. Inlet pressure 150 PSI maximum at ambient temperature (70 degrees F). 21 SCFM

Product features

  • Miniature filter with transparent bowl
  • 1oz Reservoir
  • 5 Micron element
  • 1/4″ Port size
  • Manual drain

 

How clean does my air need to be?

To know how clean your air should be, you have to ascertain and evaluate the process and application that uses the compressed air. Not all processes and applications using compressed air need an equal level of filtration. You should know this before choosing the right filter for you.

Compressed air used for pneumatic purposes can sometimes be sustained by a standard dry particulate filter which brings filtration down to 1 or 0.01 micron, nonetheless, if your process call for an OSHA-approval and removal of oil vapors, then charcoal stimulated filter should be utilized. 

Let’s understand what pollutants are and how they affect the compressed air system. 

Contaminants that are found within a compressed air system can be from ambient air that is used, likewise the compressor itself. There are three major impurities that are found within compressed air: particulates, vapors, and aerosols.

Particulates: The particulates that are found in compressed air systems are little pieces of solid material like dirt, dust, and/or pollen emanating from the ambient air, and also loose metal elements that could result from pipe corrosion. Dependent on the sensitivity of your application and/or process, contact with prospective particles can be harmful to the end product, thus causing delays in quality control and production issues, not excluding potentially displeased customers. 

Vapors: Vapors contain lubricants likewise any other liquid that has transformed to gas. Such vapors need a special carbon triggered filter to be removed from the system.

Aerosols: Aerosols comprise small drops of liquid that can be found in the compressed air system, particularly in the oil-injected compressors. Aerosols are manufactured from the lubricant, in this case, the oil that is used in the compressor, which can be damaging to both products and humans if not properly treated. 

Now that you have a better understanding of the contaminants above, let’s go a step further and look at the types of filtration methods used in removing each type of impurity.

 

Get rid of dry particulates

There are three major mechanisms used in dry particulate filters to take out solid particles of various sizes from compressed air. 

Inertial Impaction: This is a process where elements that are too heavy and can’t flow with the compressed air stream get stuck in the fiber media. The bigger the particles, the easier it’ll be to detach them. 

Interception: The smaller elements can go with the airstream, but then again, if the diameter of the element is larger than the gap of the filter media, it’ll get trapped by the filter media, making it very easy to eradicate bigger particles than smaller ones. 

Diffusion: This happens when small elements move unpredictably throughout the surface, instead of moving with the compressed air stream. This irregular movement pathway is caused by the particles that are colliding with other gas elements, this is called a Brownian movement. Since the particles possess a free range of motion and could be moved around freely, it’s more likely that they get caught by the filter media and detached from the compressed air stream. By leveraging on diffusion, separation of smaller particles is easier than separating larger ones. 

 

Why you need to consider the air quality

Compressed air contains unwanted substances, for instance, water in vapor or drop form, oil in aerosol or drop form, likewise dust. Dependent on the application area of the compressed air, these elements can harm production results and even intensify costs. The major purpose of air treatment is to produce the compressed air quality that matches your specification.

 

Can oil damage my process?

To assess the possible damage that oil can inflict in your compressed air system, you need to comprehend the basic requirements for your equipment that uses the compressed air. If your industry has severe health codes and/or your equipment is delicate to oil exposure, it’s important that you use proper purification. Let’s take a look at lubricants and get to know the effects they could have on your end product. 

Just like particulates, lubricants can get into your compressed air system from ambient air and possibly from the compressor. Facility operations like motor exhaust discharge hydrocarbons (oil aerosols) into the ambient air, thus compromising air quality and equipment failure. 

Oil injected air compressors also release lubricants within the compressed air system, which results in increased operating and maintenance outlays. Industries like semiconductor and electronics are most exposed to lubricant pollution, which could result in unsatisfied customers, product loss and missed deadlines. 

Poor purification can sometimes lead to pipe deterioration, an amplified drop in pressure and damage to equipment, resulting in expensive downtime and unforeseen repair costs. Corrosion also causes additional debris in your piping system, which in turn makes your compressor to overwork and lead to higher energy exhaustion and extra ware on compressor parts.

 

Water Is Generated Right Away

Compressors turn water vapor in the intake air into free water inside the compressor. Compressors also increase the amount of water vapor in the compressed air in the tank. Both free water and water vapor laden airWater Is Generated Right Away enter your air line and through it to your air tools.

compressor air filter

As soon as any air compressor starts pumping air into the tank, it is also pumping free water and water vapor into the tank too.

How much water ends up in your air compressor tank?

That is determined by a number of factors;  how long the compressor is running at one time, how hot the compressor gets, the volume of compressed air being used, the ambient temperature and humidity of the air flowing into the air compressors intake port… many factors, few of which you have any control over.

Essentially, there could be lots of water pumped into the compressor tank along with the compressed air.

Water getting to an air tool is a problem. If your air tool is a paint sprayer, water getting to the sprayer is catastrophic to the paint job.

Compressed air filters remove much of that free water, and some of the water vapor from the compressed air stream, as well.

If you use your air tools a lot, or if you are working with an air tool that requires freedom from water spatters and water vapor, then you want to install a compressed air filter.

 

The compressed air filter comes before other components!

Modern compressed air treatment units (FRL’s) are now usually modular, or they can be nippled together.

Ensure that when you assemble an FRL unit to treat your compressed air, that you make sure that the air travels through the filter before it arrives at other downstream components.

The filter will remove free water, and any airborne debris before it can get to and damage sensitive air-driven equipment.

 

How Do You Use The Compressed Air?

What have you got hanging on the end of your air hose from the compressor? An air tool? A spray paint gun? Just a blow gun?

Regardless, whatever you are blowing compressed air into from the compressor will likely be negatively affected by the water coming from the compressor tank along with the air.

Do your equipment a favor and add a compressed air filter.

 

What Size Of Compressed Air Filter?

A rule of thumb is that the intake port on the compressed air filter should be the same size as the air line that is feeding it. That will work for most small air compressors, as the capacity of even a mini-air filter easily outstrips the amount of air that a small air compressor can deliver.

air filter compressor

If your air compressor is more than a couple of HP in motor size, rather than use a mini-filter similar to the one shown in the photo above, consider purchasing a regular sized air filter that has the flow capacity of your compressor.

What’s flow capacity? Well, typically an air compressor can pump out about 3-4 CFM of compressed air at 90 PSI for each HP of motor size. The compressed air regulator will have a flow capacity shown on the box or the documentation that comes with the filter.

Just make sure that the capacity of the filter exceeds the flow capacity of the compressor and you are fine.

And yes, periodically you want to replace the filter element in the compressor filter as it clogs up with crud brought down from the compressor by the flowing compressed air.

 

About Compressed Air Filters – Where Install One?

As a rule of thumb of mine if it is a small DIY type air compressor, install a compressed air filter right at the coupler of the compressor. Rather than disassembling the piping, if you want to be crafty, by using another connector and coupler installed in the filter head you can then simply plug the filter into the existing coupler on the compressor with the connector in the filter, and plug the air line into the coupler on the other side of the filter head.

If you have long air line runs, know that water will condense out in the lines, and end up spraying out your air tool, even if you have a filter at the compressor.

I suggest you run the air line to a filter installed on the workshop wall, and then use another, shorter air line, to get air to your air tool.

 

About Compressed Air Filters – All compressed air has water in it

If water coming down your compressed air stream is a problem for your work or your air tools, and it almost always is, do yourself a favor. Install a compressed air filter.

The modest up-front expense may save you significantly in the long term.

Got a question about compressed air filters? Ask it below.

 

When To Use What Type Of Compressed Air Filter?

There are general purpose air filters, coalescent air filters and activated charcoal air filters. When do you use which type? This contribution by Norgren, with my thanks.

Three main types of filters exist: the general purpose filter for water and particles, the coalescing oil removal filter for oil aerosols, and the activated carbon filter for the removal of oil vapors.

norgen air filter

Use general purpose filters for main headers, branch lines, tools, cylinders, valves and valve circuits, air agitators, packaging machines, etc.

Use oil removal filters when sub-micron cleanliness or oil-free air is required, such as for the supply to fluidic devices, painting or coating processes, instrumentation, air gauging equipment, air bearings, and medical applications or areas where typical synthetic compressor oils may damage commonly used Buna rubber such as non-lubricated power circuits.

Finally, use activated carbon filters for systems where the oil vapors in the air are not acceptable, such as instrumentation, medical, or packaging systems where the compressed air may come into contact with the product, such as pharmaceuticals.

 

Some excellent advice from Norgren regarding compressed air filters….

“Filters have their flow measured in terms of the pressure drop across them. As the flow increases, the pressure drop also increases. These pressure drops are energy losses in the system.

A well-designed filter not only removes water and particles efficiently but also has a low-pressure drop at a given flow.

Be selective. Not all manufacturers quote their flows under the same conditions.

If a higher inlet pressure is used or a higher pressure drop is quoted then the apparent flow will be higher. This does not necessarily mean it’s a better unit. Often the only way to compare units is to test them under the same laboratory conditions.”

 

Replacement compressed air filter

I have a Speedaire stock # 47028a I know it’s out of production. What can I do to change the filter, if possible. If not, what would be a comparable replacement?

________________

First off, I’m guessing he’s asking about the filter element…as opposed to the whole air filter.

Unfortunately, as air components age, the manufacturer may drop or re-engineer a product, and all of a sudden, there is no support for it nor can you get parts; in this case, a filter element for a perfectly good filter housing.

Replacement compressed air filter
Most general purpose compressed air filters have at 25-40 Micron air filter in them.

If you are replacing a general purpose filter, it will be OK to visit your local hardware store (better if it was a local fluid power distributor) and ask them for a general purpose filter that is the same pipe size as yours. And, to prevent this issue for the foreseeable future, ask them for a couple of replacement elements for that filter too.

Typically there is pressure drop across a compressed air filter. The element, even when clean, creates a flow impediment that lowers downstream pressure.  If you are seeing an increasing pressure drop across that air filter, that’s the indication that the element is getting plugged up. When the pressure drop is negatively affecting the work, then the filter element  needs to be cleaned or changed out.

Here is more information on  NPT sizing,  and here is much for information about compressed air filters.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.

3 COMMENTS

  1. Bill,

    Thanks for the excellent article. I have an I-R 5HP compressor with synthetic lubricant which is eating up the seals in my Wilkerson in-line air filters (2-5 micron filters and 1 .5 micron coalescing filter). I can not seem to find in-line filters with viton seals or any seals compatible with synthetic lubricants. What advice can you give me.

    Thanks

    Fred

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