Air is dirty, whether we want to accept it or not, and we need particulate air filters because of it. Dust, oil, bacteria, water vapor, and any other particulates small enough to be picked up and carried around in the air. But the sheer amount of air makes up for the quantity of particles floating around. Compressed air brings these particles together and eviscerates the space between them. Before air has been compressed, particulate matter exists far enough away from other particles that they don’t collect together.
Air filters are designed to capitalize on this phenomenon of molecule grouping. Compressed air filters work similarly to automotive and HVAC air filters. Even though the end use might differ, they all need to remove particulate matter for the best outcome. These filters are put in place to remove solid particulates and liquid contaminants from the air, improving the quality and reliability of your system.
The principle of these filters is quite simple: They trap and remove particles from the airflow to improve the quality. The material and quantity of what is removed are determined by the size and style of the filter in place. Filters that remove the same type of contaminant can come in different sizes, and these sizes determine just how clean the air becomes. The smaller the space between filter fibers, the more that gets stopped from reaching your point of use.
The best idea sounds like going with the most minor filtration level; you eliminate everything. The problem with immediately going to the smallest level is that it clogs up quickly. When your contaminant-filled air runs into this level of filtration, it is no different than running into a solid surface with the pressure drop it causes. Having just one filter with a fine degree of filtration stops everything, including your compressed air.
To get the most out of your compressed air filtration system, you must know where you are starting and where you want to get to. And then, you work your way down from the largest filtration to the smallest. When you work your way down, you remove the larger particles before they reach the finer levels of filtration so that they do not clog the finer ones. By working your way down, you improve the efficiency of the next filter in line. Remove the larger particles with proper filtration, and then allow the finer levels to remove the finer particles.
So, we know particulate matter exists in the air around us and collects during the compression process, but what exactly is it? In reality, anything and everything that makes its way into the air stream and isn’t moisture-based is considered particulate matter. Anything from skin cells to dirt stuck on the bottom of someone’s shoe can enter the compression chamber. There are thousands of particles in the air around us, too many to be able to list, and any one of them can halt your production process given enough time.
Depending on the ISO standard your industry requires, the level of filtration necessary to achieve the desired result can change. Higher-quality air will have more stringent standards, yet most operations won’t require extremely high-quality air. Using one of the most common ISO ratings: 2.4.2, let’s break down what this means. We will use the figure below for reference.
Figure 1: ISO Standards for Compressed Air from Compressed Air Best Practices
Each of these numbers indicates a requirement about the standard of your compressed air. Starting with the first “2,” this indicates the particulate requirement. So for your particulate air filters, this is pretty important. Referencing the chart, this indicates a micron size of 1. Any iso standard with a 2 in this position will need filtration down to 1 Micron at the very least.
Looking at the “4” now, it is located in the second position, which indicates the water requirements for our compressed air. This 4 indicates that our desired dewpoint is 38°F or 3°C. So, in other words, an adequately sized dryer will achieve a dewpoint of 38°F or lower.
The first two numbers are rather straightforward: how many particles can you get away with floating around in the air, and what temperature the air needs to drop to. Things get a little trickier regarding our last number, “2,” and the oil requirements it indicates. At level 2, the oil requirements are 0.1 micrograms per cubic meter or less. This applies to everything: oil, liquid, aerosol, and vapor. The quantity of these cannot exceed .1 micrograms, yet this number may be talking only about oil mist requirements in other operations. (Luckily, with particulate filters, you won’t need to worry about this)
The most commonly used compressed air filters are particulate air filters. These filters trap and collect particles while the air compressor moves the air through the system. As the air moves, the molecules move with it, and filtration is in place to impede the movement of these particles but not the compressed air. Particulate filters rely on three main principles to remove contaminants from the air:
Direct interception is used on the largest particles and works precisely as you would think. The system directly intercepts the largest particles, working exactly as you would expect. The filter sieves the large particles directly out of the airstream. As the air passes by, the filter media catches the particles due to their size.
Another method for stopping medium-sized particles in your compressed air stream; Inertial impact changes the airflow, causing the particle to fall behind and get stuck on the filter media. Inertia keeps the particles on their original trajectory until they hit the filter and become trapped.
The finest particles in the air stream are captured using the principles of Diffusion and Brownian Motion. This phenomenon involves the random and seemingly erratic movement of these macroscopic particles. Diffusion is the solution to Brownian movement in compressed air. Diffusion causes particles to move away from one another, from areas of high concentration to low concentrations. In these cases, the molecule grouping is what you want so that when diffusion occurs, the particles will go to the lower concentration area of the filter.
Depending on the ISO standards for your compressed air, your system may incorporate one principle or all three to remove all the particulates you need. If you have less strict rules, you may only need filters that use direct interception or inertial impaction. Still, if you need all the particulates removed, you will most likely need a combination of all three methods to achieve your desired air quality.
No matter what industry you operate in or if you are just working in your workshop, you risk dust and other small particles from the environment entering your compressor. These particles are so prevalent naturally that avoiding having them in your compressed air is virtually impossible. You’re better off just planning to remove them.
If you are using your compressed air with pneumatic power tools, something as simple as a standard particulate filter sized to 1 micron. Pair this with a basic coalescer to catch the moisture and cover you from dirt to oil mists. And if you need higher-quality air for something like paint lines, you will want your particulate removal to get down to .1 microns instead of 1 micron.
Air quality is a must if you operate in an industry like food processing or pharmaceuticals. Systems that require air of this purity level will often include an activated carbon filter, which goes down to .003 Microns in size. This level of filtration catches even the smallest gas and vapor particles floating through the air. Traditional systems won’t need this filtration level, but activated carbon filters are necessary for the operations that do.
High-level filtration risks large pressure differentials due to clogs. With smaller spaces between the filter fibers, it takes less to clog them. Clogging of filter materials guarantees that pressure differentials will occur. When pressure spikes occur, they rapidly increase the pressure at the point of the element. This pressure increase can rapidly become a death sentence for your filter element. If the pressure doubled from .3 Bar to around .7 Bar, it could instantly destroy your filter element with a 200% element cost (Figure 2 below).
Figure 2: Pressure Differential Investment Costs
No matter the size of your filters, if they clog up, pressure will increase, and you can potentially destroy the entire filter element regardless of its size. All the material that should be removed would end up downstream at the point of use, due to the element . This result is the opposite of what you want for your compressed air filtration, and the solution is to ensure your filter pressure does not spike.
No matter the size of your operation or your facility’s location, you need a healthy compressed air filtration system in place to maintain long-lasting, dependable, and clean air. If the element is not replaced, the air quality will deteriorate and can lead to problems, just like the filters and your at home furnace. If you stay on top of your compressed air system, you will regularly be switching out your filters or dealing with the consequences of not.
Before you buy a set of particulate air filters, remember to look into the individual filters’ correction factors. These variables determine whether the filter truly aligns with your system or if you need to change sizes. Compressed air can get to a state that is thousands of times cleaner than the air around us and drier than any desert on the planet, but none of this is possible if the variables do not align.
To size your filters properly, you must know what kind of filters your system needs. If you need dirt and dust removed, look for a particulate filter. If you need oil and condensate removed, consider a coalescing filter. For the highest level of filtration, to clear oil mists and vapors, you will want an activated carbon filter.
When installing compressed air filtration, it boils down to knowing what your system needs. Paint and body shops will need higher-quality air filters than operations using air to move pieces along the assembly line. The needs determine the quality of the air. If you are unsure what your system needs, refer to the ISO rating for your compressed air industry.
Getting the right-sized filter can be the difference between monsoon or desert-like air reaching the point of use. The difference between a healthy compressed air system and one on the brink of falling apart is as simply as proper sizing. It might not seem like a big issue, but a few CFM differences can make a big difference.
Lastly, calculate your costs. Determine the difference between the initial and lifetime costs of the equipment. More often than not, the lifetime costs of equipment with higher upfront costs will be cheaper over time than cheaper equipment that needs repairs and replacements over the years. It may seem backwards, but when you look at the whole lifespan of the equipment, it is a no-brainer. Systems made of higher quality equipment will save you more in the long run, so why gamble on cheaper equipment.
Buy Particulate Air Filters here.
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