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If you are one of the many folks that have purchased or are considering purchasing a home compressor, you do want to have a bit of information about compressed air filters. Compressing air generates a reservoir (receiver / air tank) full of wet, dirty, hot compressed air. As the air leaves the tank, it carries the crud and free water along with it. It also carries a great deal of water vapour. As the compressed air travels to your appliance (air drill / air grinder / blow gun / air brush - what have you?) the compressed air in the air line cools, and some of the water vapour will condense into free water. That's why just having a small compressed air filter at the discharge of the compressor tank may not be enough. Even though the unit at the compressor will take much of the debris and free water from the air there, it can't remove the vapour. Even though you think your air is being filtered, by the time the air gets to your application, water may flowing out of the exhaust ports and onto your work piece, along with the used compressed air. Of course, if water flowing or blowing onto your work bothers you just a tad :~} , you'll want to add another compressed air filter just before you use the air. Many standard compressed air filters have 5 micron filter elements. If you want to know how big that is, check out the details in the Filter page on my web site. You can purchase compressed air filters with much finer elements, and you can purchase elements that are coarser, allowing much larger particulates through. Much larger is a relative term. We're still dealing with pretty small bits here. If you decide that your application needs extensive air filtration, get a micro-filter element for the additional air filter you will need. The new one might filter particulates down to .005 micron, and if you don't have a 5 micron unit upstream from it to take out the larger bits, the finer element will plug up really quickly, which is why you'll need the additional filter housing. You can purchase compressed air filter elements that will strip oil from the compressed air, these known as coalescent filters. Some piston / reciprocating, and other types of compressors too, let oil "blow by" the piston seals into the compressed air tank, and this oil will get blown downstream as you use compressed air. Compressor oil is not good for most tools that have Buna-N type seals. The compressor lubricating oil might 'eat' the seals. Each compressed air filter you install has a negative affect on the available air pressure at your tool. Pressure drop is a reality in compressed air plumbing. You could supply compressed air at 100 PSI into the discharge air line from your tank, and by the time it gets to your tool, all you have available might be 85 PSI. The flow of compressed air through the air lines, the elbows, the 'T's and yes, the air filters, all create pressure drop. If you are using your compressor a lot (make sure you know it's duty cycle so that you don't burn it out) then it would be beneficial to have an auto-drain of some sort on the air filter. A float type will open up and let water and crud flow out when the water in the bowl gets to a certain level. An electric auto-drain will be plugged into a 120 Volt outlet, and will open the bowl drain at preset intervals for a preset length of time. You set the electric auto-drain to the interval necessary to keep the filter bowl fairly empty. If the water and debris in the filter bowl gets above a certain level in the bowl of the filter, it floods the element, and now your compressed air supply is pumping water and debris through the element downstream to your tool. Did you know that water rusts metal air tool innards, and that water droplets on your work piece will not allow the beautiful paint job you are air brushing on to it to adhere? Of course you did! That's why you need a compressed air filter. One more thing. If your air consumption is great enough then even a filter at your tool may not stop the water vapour streaming along with your compressed air from condensing onto your work piece or in your air tool as the air cools. If that is a problem for you, you will need an air line dryer.
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