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The Key To Coalescing Air Filters

coalescing Filter cross section

Why Do We Need Filtration

You may be wondering why we need coalescing air filters in your compressed air system, and the answer is relatively simple: moisture and oil are bad for compressed air and they need to be removed. The air around us is not considered clean. It holds particulates, moisture and vapors from the objects in the environment.

Our lungs act as natural filters for us by removing these particulates when we breathe them in. This is no problem for us with ambient air, but your compressor is a different matter. All of the particles are floating around in very small quantities, but when air is compressed, the amount of air in a given space increases.

As the amount of air increases and the space decreases, more of these particulates are crammed into a tiny space. Like particles are going to group together and this will cause build up in your air. No matter what you do to avoid it, this is going to happen to your air due to the nature of compression.

Oil Vapors and Moisture can be extremely detrimental to your equipment with sensitive thresholds, your end products, and all of the equipment in between. Moisture particles can cause particulates to be loosened and added to the airstream. These particles are on a microscopic level but their damage is a lot larger than that.

The threat may physically be microscopic but the ramifications are definitely not. You need to make sure that these particles and vapors are removed before the product gets to your equipment or the final product. If you don’t remove it, you are only going to have problems down the line.

 

What Is So Important About Sizing

The particles in your air may be microscopic, but they are not even close to being uniform in size. Although they are all sorts of different sizes, the particulates and vapors are going to have relatively similar sizes amongst themselves. Typically you will have on size and style of filtration for each type of contaminant.

Not only does each type of contaminant have its own typical size, they also have different filtration styles. These styles typically relate to the size of the particle and thus that determines the style of filtration:

  • Diffusion (0.1 micron and smaller)
  • Interception (0.1 to 1 micron)
  • Direct Impact (1 micron and larger)

Due to the different sizes and styles of filtration, you need to cascade your filters and work your way from the largest to the smallest. If you have them in any other order, the larger particles are going to get caught in and clog up the finer filter elements. 

 

Smaller Filters Go Later

Think of your filters as screens and as the air passes through each one the windows get smaller so smaller particles can fit through the openings. You need to do it in stages so that you can get the most out of your filters. By putting the smallest ones first, everything is going to get stuck on it, and if everything gets stuck it is going to wear out your filter element almost immediately. 

Coalescing air filters are going to traditionally operate using interception methods and operating in that 1-0.1 micron range. Turbulent flow causes the particles to be forced into the element and captured. A good rule of thumb to follow is the smaller the fibers in the element, the more efficient the element will be.

Your coalescing air filters will typically be your smallest degree of filtration and be the final step of filtration before the air reaches the dryer. This way, you remove the larger particles first so that the finer filtration does not get overwhelmed.  

 

What Does a Coalescing Filter Do?

Coalescing filters remove oil vapors and moisture from the airstream. They function similarly to general-purpose filters, just with a much smaller space between the fibers. The space can be as small as .01 Microns to capture aerosols and force smaller particles to merge. Without a larger filter in front, these filters will become clogged and unable to filter anything.

Coalescing filters work based on 4 stages:

  • Air Intake
  • Filtration Process
  • Coalescing of Particles
  • Air Outlet

Figure 1: Filter Components Diagram

 

Airflow in a Coalescing Filter

The air intake is the entrance point for your compressed air entering the filter. Air flows in from the piping and previous filtration steps. It then travels down through the casing into the filter element to begin the filtration process. The filter element is our coalescer, specifically designed to capture moisture vapors and combine smaller particles into larger ones.

The filter fibers impede particle movement as the air passes through the filter element. By using such fine filters, you can take advantage of the natural properties of diffusion. The particles’ random movement causes them to stick to the fiber while the air flows through without problems. Coalescing filters can simultaneously remove the smallest particulates and aerosol particles without reducing filtration efficiency.

After the air passes through the element and filtration has occurred, the particles coalesce together and fall into the chamber at the very bottom. The combination of particulates and liquid will be stored until it needs to be released from the drain. Typically, this drainage will be run through an oil-water separator so that the condensate can be dumped without polluting the local environment.

While particulates and moisture are dropped down, the air flows back up through the center of the filter to continue downstream. The air outlet is in line with the air inlet, allowing for continuous flow of compressed air needing to be treated. Typically these coalescing filters will be the last line in your filtration system. The air will exit the coalescing filter and repeat the same process in an activated carbon filter for extremely high-quality air.

 

Why Do You Need A Coalescing Air Filter?

Coalescing filters are a necessary component of any healthy compressed air system. Even the slightest quantity of moisture can destroy your system from the inside out. Your coalescing filters remove small droplets that manage to make it past the dryer to ensure no moisture makes it downstream. 

Implementing a Coalescing Air Filter provides the following benefits:

  • Efficient Removal of a variety of fluids
  • Micron Ratings with efficiency levels of 99.99%
  • Eliminates the maximum amount of moisture and particulates for high-quality air
  • Reduces maintenance costs and operational expenses over time
  • Ensures the safety of downstream equipment
  • Reduces downtime and maintenance costs from increased filtration efficiency.

 

The benefits of filtration can be overlooked and attributed to other factors at play in your compressed air system. Considering that filters do all their work out of sight, their benefits are often unrealized. The particles are so small the human eye can’t even detect them all. Although you may not be able to detect the differences yourself, your system and wallet will reflect the impact of efficient filtration.

Internal wear and tear lead to unwanted downtime, and one of the leading causes is moisture remaining in your compressed air. Without a coalescing filter, the air will slowly cool down as it travels downstream. When the air cools, its moisture will drop out downstream, leaving your point-of-use equipment with lower-quality air. 

 

Additional Considerations

Coalescing air filters have the finest filter elements for removing moisture and particulates from the airstream. Some have a diameter of .01 microns, so the space between the fibers is minuscule.  If larger filters are not in place prior to these filters, the element will become clogged almost instantly. The filters are designed to remove particulates and moisture that slipped through previous layers of filtration. 

If you are planning to use coalescing air filters in your compressed air system, ensure you have a proper filtration in front of it. Without it, your filter will be no different from a wall impeding compressed air flow. You need to cascade your filters from the largest size down to the smallest, whether that is a coalescing filter or an activated carbon filter. 

Coalescing filters cannot remove everything from the airstream; vapors are too elusive to get caught in the element. Specific industries, like pharmaceuticals, have standards (figure 1) that require all oil vapor to be removed from the air. Applications like this require a higher level of filtration than just a coalescing filter; adsorbing filters are necessary to achieve this.

 

Filter Classifications

Figure 2: ISO 8573 classification ratings

Different ratings require different levels of filtration to reach them; higher levels of filtration result in higher-quality compressed air. Various levels of oil, water, and solid particles are allowed in different industries, so just make sure you are aware of yours before buying new filters.

Even if you do not need a higher level of filtration, there are a few potential setbacks:

  • Higher Initial Costs
  • Element Replacements
  • Poor Filtration Resulting in a Useless Element
  • Heavy Hydrocarbon Build-up

The downside of higher levels of filtration is that they cost more upfront. Higher-quality air requires a more significant investment. Unfortunately, better filters cost more and require more precise construction during manufacturing. However, you are investing in the health of your compressed air system rather than just buying another component for it. 

Filter elements remove condensate and particulate matter from the air stream, and these particles get stuck in the element over time. After enough time has passed, nothing will be able to make it through the filter element, air included. To keep your filter as efficient as possible, you must routinely change your filter elements. Not changing the filter element will cost more in the long run when you experience unplanned downtime.

Material build-up occurs outside the field of vision, the only way you can truly tell is by keeping an eye on the state of your filter element. Routine checks, although annoying at times, help you keep tabs on the current state of your equipment. Preventing build-up will save you time, money, and headaches in the future.

 

Get Your Own Coalescing Air Filter Today

If you have decided your system needs coalescing-style filtration, you are in the right place. Warthog offers the best coalescing filters on the market. From the Nano GFN filters to the Atlas Copco UD+ series, there are options to fit any system for any industry. Whether you need the highest level of filtration or just want to ensure that moisture and particulate matter are removed, you will want one in your system.

Options like the Atlas Copco UD+ provide the best of both worlds. The filters are constructed to adequately remove particulates and moisture without sacrificing pressure drops and filtration efficiency. These models combine the filtration steps of the particulate and coalescing filters into one-stop, saving you money and space.

 

 

These filters are excellent for operations trying to maximize their operational space. They reduce the total space used by the filters, reduce the distance the air needs to travel and increase the efficiency of air delivery. If you are not worried about achieving the highest-quality air and just want to ensure your air is clean enough for use, an option like the UD+ could be precisely what you are looking for.

You can find the best coalescing filters from the best brands at Warthog. We only carry the best family of brands and their equipment. We have you covered if you need high-quality compressed air equipment in your system. With the toughest brands backed by unbeatable support, there is no better air compressor marketplace.

 

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