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The Importance of Sizing Your Compressed Air Filters

compressed air filters

So Why Do I Need to Size My Compressed Air Filters?

For starters, what is a compressed air filter? Why do you need one in place on your compressed air system? The answer is quite simple. The air around us isn’t that clean, and when air is compressed, all those particles that were floating around are now grouped together, and they need to be removed from the air.

That’s what your filters are for, to be placed in the air stream and collect the particulates and moisture. Filters are a piece of ancillary compressed air equipment that removes aerosols, particulates, or vapors. Aerosols are small liquid droplets, particulates are little solid particles (dust, dirt, rust), and vapors are liquids that have been converted to gas.

Compressed air filters clean compressed air, crazy right? They typically come in three different styles of filtration: General Purpose, Coalescing, and Activated Carbon. Each variation is used to remove different types of contaminants in the air. General Purpose filters are for solid particulates, coalescing removes oil aerosols and water vapor, and the activated carbon removes oil vapor and odor.

So just how much stuff is in compressed air? Well, when you take one cubic foot of compressed air, it can contain millions of dirt particles, considerable amounts of water and oil, and even heavy metals like lead, cadmium, and mercury. If these contaminants are not filtered out, they can cause long-term damage to components like valves and cylinders.

With this conglomeration of particles and aerosols mixed in the air, you need to remove it before it contaminates valves and seals and reduces the lifespan of these components. If you want to prolong or maintain your products’ lifespan, you have to size your filters properly. There are no if’s, and’s, or but’s about it.

Sizing your compressed air filters is no guessing matter but rather a calculated procedure. Making sure you select the correct air filter for your industry or government standards is essential. Without ensuring compliance, you may risk whether or not your end product will meet your set criteria and if you can even sell it. 



How Do I Find My Compressed Air Filter Size?

The size of your compressed air filter is determined by the size and type of particles that are being removed. You want to be able to remove the particles in descending size so that you do not clog up the filter elements. The bigger particles will get caught as the air passes through and smaller and smaller particles make it through.

There are a few things you need to consider when you are looking to buy an air filter. These will be the guiding principles for how you select your compressed air filters.


Extraction Efficiency

This is the percentage of dust that is removed or extracted from the air. So with a filter that is sized to 1 micron, it would have a 99.8% extraction efficiency because .2% of the particles that size pass through the filter.


Flow Rate

Flow rate is the amount of air that passes through the filter in a given period of time, usually measured as Cubic Feet per Minute (CFM). Your filter size has to match your flow rate, so if you have a larger flow you are going to need larger compressed air filters. If your flow rate is either too much or too little for your filter it can cause unwanted pressure spikes and drops.


Flow Resistance/ Dust Capacity

Flow resistance is alluding to the build up of dust and debris in your filter over time. As this builds up more and more dust will accumulate and can cause pressure drops and restrict the flow of your compressed air. Stay on top of this by routinely replacing your filter elements and preventing extreme build up.

These are the main concerns you should have when determining your filtration sizing, beyond that there really isn’t much else to keep in mind aside from pressure drops, and all that takes is a simple calculation.


Calculate Your Air Filter Pressure Drop

Before we get to the formula we need to go over what all of the individual variables are so you can understand the why behind the formula and make it just a little bit easier to calculate.


  • P= Pressure drop (psid)
  • q= Rated flow (SCFM) at standardized conditions (100 psig & 100 ºF)
  • q1= New actual flow (SCFM)
  • P1= actuale operating pressure absolute (psia = psig + 14.7)
  • T1= actual operating temperature. Measured in Kelvin (°K = °F + 459.67 often rounded up to 460)


Now all you have to do is gather your information and plug it in to find your exact pressure drop with your current conditions so you can make sure you are getting the best filter for your system.


Stay On Top Of Your Filters

As we noted before, your filter elements aren’t going to last forever, because if they are doing their job there should be build-up. If you let them go too long the build-up will be out of control and become a hindrance to your system. Replacing your elements is a simple yet easily forgettable task.

Staying on top of your filters requires you having the correct elements to replace yours and having them on hand when you need to switch them out. A good practice to avoid getting caught needing a filter and not having one is to always have at least one spare element on hand. Being prepared can prevent unwanted downtime, and make sure that you can keep production up and running.

Now don’t go running off thinking you can get away without changing or replacing your filter elements. Compressed air filters are subject to the ISO 8573 standard; this determines the acceptable quantity of solid particles, water, and oil in the air. They also provide general information on pollutants present in compressed air.


Just A Few Things Before You Go

Sizing your compressed air filters requires knowing a bit about your compressed air system and how it operates, but so does almost all compressed air equipment. Odds are you will have the information you need on hand or be able to find it easily in the manual or on a product page if we carry it. 

Remember, just like your filters, your filter elements are rated by size and should be sized according to flow. Now if you know your filter size and the style of element you need you’re all set to pick out the element that you need. Depending on the degree of filtration your filter element can range in size from 25 Microns to .01 Microns.

As long as you make sure your filters are in the right order for size and filtration style to make sure you are not having pressure disparities or restricted air flow. You want your contaminants removed and your air to keep moving, nothing more and nothing less. Too little flow will prevent proper filtration and we already know what too much can do.

Follow the key points to sizing your filters, account for any abnormalities or variations that could occur and change your air flow. You don’t need it down to the specifics but you do need to have an understanding of the airflow requirements for your compressed air system.



Get Your Own Compressed Air Filtration

You’ve found the perfect spot for getting compressed air filters and their replacement elements for your compressed air system. From replacement element subscriptions to getting the best filter housing on the market. If you are interested in getting on the subscription program for your own just text us at (864) 894-1400 and ask for the filter subscription.

To get your own and check out some more information on our compressed air filters. We have products from the best, with brands like Atlas Copco, Nano Purification, and more available, alongside our wide selection of filter elements, Warthog is the home to keep your air clean.


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