Compressed air filters help to keep the air clean and condensate free to protect equipment from dust, dirt, pipe scale, oil and water. Even though the compressed air system will typically have a main dryer, additional treatment is often necessary. For this discussion, we will focus on the oil removal process and filter type.
After the compressed air has passed through a particulate filter, the dirt, dust and water droplets have been removed. Oil that is present is much smaller in size, and mostly passes though the particulate filter. The installation of a coalescing filter will provide for the removal of the majority of the fine oil aerosols that remain. The coalescing filter works differently than the particulate filters. The compressed air flows from inside to outside through the coalescing filter media. The term ‘coalesce’ means to ‘come together’ or ‘form one mass.’ The process of coalescing filtration is a continuous process where the small aerosols of oil come in contact with fibers of the filter media. As other aerosols are collected, they will join up and ‘come together’ and grow to become an oil droplet, on the downstream or outside surface of the media. Gravity will then cause the droplet to drain away and fall off the filter element.
Some important information to keep in mind –
Change the filter regularly, not just when the differential pressures exceeds recommended limits, typically 5 PSI
Coalescing filters will remove solids too, at a higher capture rate due to the fine level of filtration, using a pre-filter for solids will extend the life
Oil free compressors do not provide oil free air, as the atmospheric air drawn in for compression contains oil vapors that will cool and condense in the compressed air system.
If you would like to talk about oil removal filters or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
Compressed air systems will contain contaminants that can lead to issues and increased costs through contamination of product, damage to the air operated devices, and air line clogging and restriction. Proper air preparation is critical to optimizing performance throughout the plant operations.
Because there are different types of contaminants, including solid particles, liquid water, and vapors of water and oil, there are different methods of filtration, each best suited for maximum efficiency in contaminant removal.
Particulate Filters – The compressed air flows from outside to inside of the filter element. The compressed air first passes through a baffle arrangement which causes centrifugal separation of the largest particles and liquid drops (but not liquid vapors), and then the air passes through the filter element. The filter element is usually a sintered material such as bronze. The filter elements are inexpensive and easy to replace. Filtration down to 40-5 micron is possible.
Coalescing Filters – This type operates differently from the particulate type. The compressed air flows from inside to outside through a coalescing media. The very fine water and oil aerosols come into contact with fibers in the filter media, and as they collect, they coalesce (combine) to form larger droplets towards the outside of the filter element. When the droplet size is enough the drops fall off and collect at the bottom of the filter housing. The filter element is typically made up of some type glass fibers. The coalescing filter elements are also relatively inexpensive and easy to replace. Filtration down to 0.01 micron at 99.999% efficiency is possible.
Adsorption Filters – In this type of filtration, activated carbon is typically used, and the finest oil vapors, hydrocarbon residues, and odors can be be removed. The mechanism of filtration is that the molecules of the gas or liquid adhere to the surface of the activated carbon. This is usually the final stage of filtration, and is only required for certain applications where the product would be affected such as blow molding or food processing.
When you work with us in selecting an EXAIR product, such as a Super Air Knife, Super Air Amplifier, or Vortex Tube, your application engineer can recommend the appropriate type of filtration needed to keep the EXAIR product operating at maximum efficiency with minimal disruption due to contaminant build up and unnecessary cleaning.
If you have questions regarding compressed air filtration or any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
I would like to dive into the realm of filters and regulators. Majority of EXAIR products use compressed air to coat, conserve, cool, convey or clean. So, to keep the product running efficiently, we need to supply them with clean, dry, pressurized air. We offer a line of filter separators, oil removal filters, and regulators that can supply enough pressure and flow to keep the EXAIR products performing for a very long time. If we look at each individual item, we can see how they can play an important part in your compressed air system.
Regulators are used to control the amount of air pressure being supplied to your EXAIR products. This is important if you are trying to control the flow, force, and/or conveyance rate. One issue with regulators is “droop”. Droop is the amount of pressure drop when you flow through a regulator. If you set the pressure of a regulator with no flow, to let’s say 80 psig (5.5 barg). Once you start flowing, you will see the downstream pressure fall. This is dependent on the size of the regulator and the valve inside. This is very important because if you need 80 psig (5.5 barg) downstream of the regulator feeding an EXAIR product and the droop brings it to 30 psig (2 barg), you will not have enough flow for your EXAIR product, losing performance. EXAIR recommends a specific regulator for each of our products. We tested our products with the recommended regulators to make sure that you are able to get the best performance. If you do use another manufacturer’s regulator, make sure you are able to flow the correct amount of air at the pressure you need. Not all ¼” regulators flow the same.
Filter separators are used to remove liquid condensate and contamination from the compressed air stream. They have a 5 micron filter and work very well if you get a slug of water or oil into your compressed air system. They use mechanical separation to remove the large particles of dirt and water from the air stream. Most facilities have some type of compressed air dryer in their system. This will dry the compressed air. But, if a system failure occurs, then water, oil, and dirt are pushed into the compressed air lines and perhaps into your EXAIR products. Even if you have good quality air, it is important to keep your products protected. An ounce of prevention ….
The oil removal filters are used to keep the compressed air even cleaner yet. They work great at removing very small particles of dirt and oil. Without an oil removal filter, dirt particles and oil particles can collect in “dead” zones within the compressed air lines. Over time, a tacky glob forms. As it grows, it can break off and get into the air stream affecting pneumatic devices. The oil removal filter will be able to help eliminate the long term effects in your compressed air system. As a note, oil removal filters are not great for bulk separation. If you have a system with lots of water, you will need a filter separator in front of the oil removal filter to optimize the filtration. With the oil removal filters, the media is a barrier to collect the small particles of dirt and oil. If a slug of water or oil tries to go through, it will block a portion of the element off until it is forced through. This will increase the velocity and pressure drop of the element. With the high velocity, as the slug makes its way through the media, it can spray, re-entraining the liquid particles.
Now that we went through our pneumatic products, how do we use them together to get the best supply of compressed air? With both types of filters, we always want them to be upstream of the regulator. This is because the velocity is lower at higher pressures. Lower velocities mean smaller pressure drops which is good in filtration. If we can analyze the compressed air systems, I would like to categorize it into a good and premium quality. To supply a good quality of compressed air, you can have the compressed air run through the filter separator then a regulator. To produce the premium quality of compressed air, you can have your compressed air run through the filter separator, the oil removal filter, and then the regulator. With clean quality air, your EXAIR products will provide you with effective, long-lasting performance without maintenance downtime.
Have you ever walked into an industrial plant and noticed a “fog” in the air? If they have pneumatic equipment, then it is a good chance that it is an oil mist. With many pneumatic devices, they need oil to lubricate the o-rings and cylinders for functionality and life. This is generally done with a lubricator. A lubricator puts a small amount of oil in the compressed air line to coat the inside of valves and cylinders. The problem becomes when the valve switches or the cylinder retracts, the excess air is exhausted into the atmosphere. And with that air, there is a fine mist creating the “fog”.
Most pneumatic equipment will have some type of muffler to reduce the noise. Typically they are a sintered bronze muffler. They work well in noise reduction, but they do not capture the oil. OSHA (Occupational Safety and Health Association) has a requirement for operator’s exposure. Under the standard 29CFR 1910.1000, the cumulative exposure for a worker is 4.32 PPM (parts per million) for an 8 hour shift and a standard 40 hour week. As EXAIR Corporation is a leader in safety with compressed air systems, we created a muffler with an oil coalescer, or our Reclassifying Muffler. The Reclassifying Muffler will be able to accomplish two things: 1. reduce the noise level, and 2. remove the oil from the exhausted air. The complex matrix of fibers absorbs the noise caused by the pressure relief. Also, this same complex matrix of fibers creates a tortuous path for the oil particles. It will collect on the fibers and coalesce into larger particles. The larger oil particles will now be able to have gravity move the residual oil down the side of the Reclassifying Muffler. At the bottom, we have a sump that will contain the waste oil and a ¼” tube adaptor to discard it safely away. We have a range of sizes from 1/8” npt to 1” npt depending on the amount of exhaust air flow. In some instances, you can manifold the lines together to use one larger Reclassifying Muffler. An instance of this would be many small valves inside an electrical cabinet that would need to have the exhaust air removed. With our range of Reclassifying Mufflers, you will not have to walk around in the fog.
Last week I pointed out the important locations for measuring your compressed air system pressure throughout your compressed air system. One of the critical points to measure system pressure was before and after each filter. This leads into another question that I receive every once in a while, “How do I tell when the filter needs to be changed?” The answer to this is easy, when you see more than a 5 PSIG pressure drop across the filter. This means that the element within the filter has become clogged with sediment or debris and is restricting the volume available to your downstream products.
This can lead to decreased performance, downtime, and even the possibility of passing contaminants through the filter to downstream point of use components. In order to maintain an optimal performance when using EXAIR filter separators and oil removal filters, monitoring the compressed air pressure before and after the unit is ideal.
Replacement filter elements are readily available from stock, as well as complete rebuild kits for the filter units. Changing the filters out can be done fairly easily and we even offer a video of how to do it.
The life expectancy of a filter element on the compressed air is directly related to the quality of air and the frequency of use, meaning it can vary greatly. If you tie a new filter onto the end of a compressed air drop that has not been used in years, you may get a surprise by the filter clogging rather quickly. However, if you maintain your compressor and your piping system properly then the filters should last a long time. Generally we recommend checking your filters every 6 months.
If you have questions about where and why to filter your compressed air contact us.
The video below will give a brief demonstration on the importance of point of use filtration in order to remove unwanted material such as water, scale, particulate and oil from your compressed air stream. Point of use or end-use filtration will keep your air clean and your compressed air products running smooth. If you have any comments or questions, please feel free to contact us.
I would like to discuss the importance of clean and dry filtered air. This all comes from some discussions I have had with customers over my time here at EXAIR, as well as from my time in the machine tool industry. It is notable to state that we simply ask for clean/dry air to run through our products, not “instrument” or “process” air which is typically held at a different pressure, temperature, or volume and can be more expensive to generate. All of EXAIR’s products use general plant air and can be cleaned up with simple point of use filters.
Clean and dry compressed air is essential for ensuring a long and easy life of almost any compressed air product. One product in particular that I have some data on is the EXAIR Line Vac. The pictures below show the inside wall of a Stainless Steel Line Vac. This unit was used in a harsh outdoor environment. The compressor was not maintained and did not have any form of filtration on the lines feeding the Line Vac unit. The first picture shows where all the dirt and particulate were impacting the internal generator wall as it entered the air chamber.
The two dark grey marks are actually the impact points on the unit. There is only one air inlet on the Line Vac, this means that the unit was taken apart during the two months and actually inspected then put back together and the generator was rotated slightly during this process. These spots are similar to what sandblasting does to metal, just to illustrate how much particulate was in the air stream. Since the air has not yet reached its full velocity within the Line Vac, it has left only those visible surface blemishes.
As the air begins to exit the array of small generator holes it begins to rapidly increase in velocity while it is trying to expand to atmospheric conditions. Because of this increased velocity, the wear the generator holes experience is greater and as seen below it is causing some extreme wear.
To give you an idea of what a new generator should look like is below. Here you can see uniform holes that go precisely through the generator.
To prevent a disaster like this from happening to your end-use compressed air products, all you need are some simple, low maintenance filters. EXAIR offers dirt / water filter separators that will filter your compressed down to 5 micron particulate size. The will catch the good majority of rust, water, and dirt within your compressed air system. Then you can also install an oil removal filter which will filter all oils and particulate out of your compressed air system down to 0.03 micron particulate level.
Each of these units are great point of use filtration to keep any of your processes from experiencing what this Line Vac experienced. If you have any questions about the quality of your compressed air or why you are seeing failures in product on your compressed air system, contact us.