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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Canister Filters Versus Needle-Felt Filter Bags 
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Filter-bags are easy to clean. Just give them an occasional shake to dislodge any dust-cake. When a thorough cleaning is desired, simply turn the bag inside/out and vacuum. Life expectancy is high with well-constructed needle-felt bag-filters.
From contributor M: Like you, I have a small shop. Moreover, I have an Oneida system and their filters will not collapse from running compressed air across them. You only need a small air compressor, so that shouldn't be a huge expense (look for a used one). Having owned Grizzly equipment in the past, I can personally attest to the fact that an Oneida will most likely have a higher quality motor. From contributor J: I am also looking at the Oneida systems and particularly a 3hp one. As for blowing out a filter, if you're worried, just turn your air pressure down. Just because your compressor can produce 100+ psi does not mean you have to use it! From contributor I: I have an Oneida system and usually clean the filter by running my hands around them. The filter is quite stiff. You can also tap it gently on the ground to dislodge the trapped dust. From the original questioner: Thanks everyone for the info. What do you mean by running your hands around the filter? I presume there is no external mesh covering the pleats and that you can touch and stir the pleats enough to break the internal clogging. Assuming that method of cleaning the pleats is not injurious, I would think that a light brushing from the inside would be no more harmful. Do you agree? I have a Wynn cartridge filter for my Delta single stage to which I have added a trashcan second stage. The filter worked wonderfully at first, but owing to my poorly designed system, it clogs too quickly and I think that I broke an internal seal by a mite too "gently" tapping it on the ground to clean it - as I can now smell wood chips when I run the DC. The cartridge has metal mesh around the inside and outside so I cannot stir the individual pleats. Rick Wynn thinks I might be able to fix the filter, which I very much appreciate, but what I really need is a properly designed system - hence this thread. Where do you guys put the Clear Vue system in the hierarchy?
From contributor B: Just a few thoughts here regarding cartridge filters. I know they're all the rage these days on consumer model dc's. Internet logic usually refers to the added surface area of the filter. Little thought is ever given, however, to the applicability of those filters to handle wood waste. Cartridge filters are well known in the world of industrial dc's. They are, however, used primarily with dc's that provide flow-reversal, or "pulse-jet" cleaning. These pulse-jet systems use blasts of high-pressure air to constantly clean the filters during use. This is done to reduce pressure drop. Woodworkers often tend to view filters only from the woodworker's perspective. Filtration, however, covers just about any manufacturing process you can imagine. I've seen countless discussions about "the huge surface area" of a particular cartridge filter, with absolutely no thought given to the intended application for that specific filter. It may have been designed to deal with vapours, or mists, or smokes, for example. The tight pleats of such a large surface area render this type of filter inappropriate for wood waste, especially without flow-reversal, or pulse-jet cleaning. Even companies like Oneida recognize this. They offer the option of needle-felt filtration. Even with their cartridge filters, they tend to go with smaller surface areas. I believe Oneida's most expensive filter is 5 feet tall, 18" diameter, yet only has a surface area of 145 sq. ft. That filter also sells for $345 US. That particular filter features extra-wide pleats, and adds an Axtar coating for enhanced particle release. It's not there for no reason. Inappropriate filter selection will lead to very short-term gain. When clean, these filters will have very low pressure-drop. Airflow will appear to be stellar. That will change very quickly, however, as the filter loads. That effect is particularly pronounced when using cartridges on a single-stage dc. In your post, you blamed "your poorly designed" second stage pre-separator. I think you'd be well-advised to reconsider your filtration choice. If your single-stage dc is the typical single-filter with plastic lower bag, consider twin needle-felt filters mounted to your bag-tree. You've already stated that you're using a pre-separator. Wood waste can include a wide variety of particulate size and density. Wood flour, the very lightest waste, is particularly troublesome to deal with. It only requires very low velocity for particle suspension, and you can bet that much of it will end up in the filters. It's that waste which will load your filters most quickly. With planer shavings, for example, you could probably fill your dc to a point where even the top filter is full of shavings, and yet notice very little suction-pressure drop-off.
From the original questioner: Thank you very much for your considerable and informative reply. Pulse jet cleaning must be the "industry standard practice" to which Oneida refers. I presume the small-shop method of grabbing an air hose and blasting the filter is not nearly as effective or conducive to long filter life as a commercial system. I have a Delta 50-760 with the trash can immediately below the intake and sitting inside the cart. I opened (tricky job, by the way) the Jet separator lid to 5" on both intake and exhaust to match the 5" intake of the Delta. The poor design is of my making, of course, in that the power of the 760 sucks clean the trashcan of everything but the heaviest items. Thus, the filter takes all that fine dust. The cartridge I tried clogged rapidly, as you indicated. I have estimated the brush cleaning system of Grizzly to be more effective than trying an air hose. I don't see how I could evenly blow the insides clean without a series of nozzles - spaced 360 degrees around the cartridge - and all blowing at just the right distance and pressure. Running a brush - designed for the filter - down the insides seems a better system. What do you think?
From contributor B: I think a canister filter is totally inappropriate for a single-stage, period. It's an idea born on hobbyist dc sites. It's ill conceived. The logic was that if the surface area was larger, it has to breathe more freely, but that is not always the case, as you've discovered. In fact, the only air permeability rating I've ever seen posted for the canisters is roughly 20cfm/sq.ft. A quality needle-felt filter should get you three times as much. 55-60 cfm per sq. ft. Your original filter on that new model Delta 50-760 is probably one of the best quality consumer dc filters out there at the moment. Plus, it's an oversized filter of 20.5 sq.ft. of surface area. There's simply no need for a canister filter. Air-permeability is not your problem, it's loading of the filter. This is to some degree to be expected with a single-filter dc. It's not the larger waste that will reduce your dc's efficiency, it's the very fine wood flour. You stated that your pre-sep is being sucked clean. That's not unusual. Your suction is obviously strong enough, you simply have to tweak your pre-sep a bit. Frankly, I don't know why you'd even bother with a pre-sep on that dc. If your suction is strong at your machines, there's really no point. You have plenty of waste capacity in your lower collection bag. Pre-separation only becomes an issue if your suction at source is inadequate, due to filter loading. If you absolutely want a pre-sep, that's fine. You'll have to tweak it somewhat. When you use a fairly powerful dc and a small-capacity pre-sep, you'll often find it sucked clean. There are multiple ways of dealing with that. One way is to reduce outlet velocity below particle suspension levels. If you're using one of those garbage can lids with 4" porting, get rid of it. Those are fine with a small dc, like a 1 hp model. For your 11.5" impeller, you'd be better off making your own pre-sep. You can make a drop-box type, or simply, a drum with a wooden lid. If you make a drop-box, that pre-sep's inlet might be 5", for example. Your outlet should be larger if possible. The larger you make it, the lower the outlet velocity, and the less chance there is for particle suspension. You could, for example, use two 5" outlets connected with a 5x5x5 wye, then run your 5" pipe to the dc. That will drop your outlet velocity in half. Inside the drop-box, place a "knock-down baffle" just in front of the inlet. The entering waste should strike that baffle, shedding velocity, and dropping into the box. Don't expect to capture 95% of the waste. There will be some turbulence, and the lighter waste will still be transported to your filters. This type of pre-sep should be able to capture much of your bulkier waste, especially that from a jointer or planer. If you choose to use a drum with a wooden lid, you have to watch the proximity of the inlet and outlet pipes. Otherwise, you'll find that the waste simply traverses across the narrow gap between the pipes. That's what's happening with your current pre-sep. If it was transparent, you'd see that. To deal with that, you might want to use an elbow inside your pre-sep. This will give a chance for the waste to be projected against the inside surface of that drum, shedding velocity. Slow down the outlet velocity by using oversized pipe. You'll not only have more effective pre-separation, but your pre-sep will also have lower overall resistance. If your drum-lid has room for the twin 5" pipe outlets, that's good. If not, go with an 8" outlet, then use the appropriate reducers. HVAC reducers are commonly available at your local hardware store, and they're dirt cheap. I'd also go with an oversized elbow at the inlet, if you're using an elbow there. Again, to reduce resistance. Just to give you an idea of your velocity, let's say you're pulling 600 cfm through a 5" pipe from your source machine. Well, the velocity through the pipe will be 4403 fpm. The waste will enter the pre-sep at that velocity. You could slow that entry velocity somewhat, by using some 6" pipe before the pre-sep, and a 6" or larger entry elbow. With 6" pipe, entry velocity would be 3057 fpm. Now, with a twin 5" outlet, your outlet velocity will be 2200 fpm. That's well below particle suspension level for larger, denser waste. Still, that velocity will suspend a lot of your fine waste. Not a problem with a planer or jointer, not a major concern with your table-saw, but not ideal with a wide-belt sander. If you used an 8" outlet, your velocity would be 1720 fpm. You'll have to tailor your pre-sep to your individual requirements. It may take a few attempts, but I'm quite certain you can make a reasonably effective unit for the cost of a few inexpensive HVAC elbows, wyes, and reducers. They're only about $3 - $5 a piece.
From the original questioner: Excellent info. I'm going to try a 5x5x5 wye fixed to the underside of the lid (so that the two 5s are inside the can and the single 5 is protruding up through the top and feeding in to the DC). I presume this will slow the air entering the two 5s - and that's the goal - but that as the two 5s converge, the airspeed will pick back up as it heads into the impeller. Am I right? If I am, that seems to be the easiest fix at the moment. I'll let you know how it works. From contributor B: Well, basically, you are right, but I'm not sure I'd want to put the wye inside the pre-sep. Have you reviewed the related Knowledge Base areas below? 
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