Augmenting Dust Collection with Air Filtration
From contributor D:
"Dust collection is a must, but it doesn't do anything for residual dust in your air." It does if you have a properly sized vacuum unit. Our interior air is replaced every few minutes.
From contributor F:
"It does if you have a properly sized vacuum unit. Our interior air is replaced every few minutes." Are you saying youíre running your dust collector all day long to double as an air filter? That doesn't seem very practical. I have a 7-1/2 hp cyclone and run it when needed. I wouldn't want that thing running all day long both for the noise and the electrical bill! My smaller air filter is probably 1/3 hp and you can barely hear it running. The larger ones are maybe 1/2hp and sound like a typical forced air furnace.
I have to assume if youíre replacing your air youíre just dumping everything outside (no filters). Nice if you can do it, but the original questioner cannot, plus at least 1/3 to 1/2 the country has to heat their shops in winter, so another reason it's probably not a great solution in general. Not sure the average fabric bags on dust collectors collect as fine as a half decent furnace filter or not? I do know with my bags (Beane fabric) there's always a faint plume of dust when I fire it up. There's more than one way to skin a cat so if it works for you great. I just don't see it being practical to use a dust collector as a shops air filtration for most shops.
From contributor D:
We can exhaust the filtered air outside because of our southern location. The collector runs all day because I have 20 or so machines with most running full time. No, you are right, it is not practical for smaller shops.
From Contributor O:
The first rule is to collect as well as possible at all the sources. Seal up cracks, and make or buy good hoods that do everything to capture dust where it is made. If you use routers, have enough of them that you can fashion hoods for each cut, or use them in a table so collection is made easier. Or convert to a shaper since they are designed to collect dust, whereas routers are not. We are now using Festool sanders with the vacuums, and it has almost eliminated sanding dust in the shop. The vacuum hose adapts to other small tools, and collects at the source very well.
Secondly, maximize the suction you have - sealed fittings and tight fitting blast gates. No long runs of corrugated hose or no tight radius elbows. Itís smooth, easy and tight. Just a few leaks here and there can cut efficiency a bunch.
Next you have to drop the dust out of the airstream with a cyclone - or two in your case. This has to be sized to the CFM of the fan and ductwork. Then, you need to filter the air. I know nothing about cartridge filters, but have a lot of experience with socks or bags. Make sure they are effective and have additional capacity so the air can move through them back into your shop. Shake them down once or twice a day, or make a timed shaker grate. Some filters like to have some cake on them, others do better with shaking to eliminate it. You may benefit from contacting someone like Oneida Air. Give them a shop layout with the CFM req'd at each machine and let them engineer a system for you. The ones they have done for me are flawless and pay for themselves in better productivity - no unnecessary fiddling with the system at all.
Clean your air as well. It will make for a better environment, more productive and make the shop a pleasant place to be. I moved my collector into a separate room and soundproofed it all so the shop is clean and relatively quiet. Put the DC on a remote control so it is easy to switch on or off.
From contributor J:
If you still have lots of dust in the air there is something off with your system. Leaks, faulty hoods, underpowered, improperly sized ducts, whatever. Do you have a supplemental filter after your cyclone? That might do it. See what Oneida says, they have a good rep. In the old days, I would go to the fabric store and blow through every bolt of denim they had to find a decent filter, then sew my own bags. They worked, but not so well. Nowadays I go to a bag supplier and for barely more than the cost of the fabric they will sew it better than I ever could to my design. Plus the fabric is engineered for the job and works much better.
My collectors are bag type, sometimes with homemade cyclones to take out the chips. I also use a very quiet homemade air cleaner: a 3 Hp radial blower ducted to one end of an oversized filter bag, with a sheetrock bucket band clamped to the other end. It's oversized so superfines aren't pushed through (there is actually no such thing as half micron rated fabric, filtering ability depends on weave, coating and air pressure). There is very little load, which means the blower is very quiet, unlike the collectors. I hit it with a stick every once in a while, but the cake falls off on its own. It is tied up to the ceiling running horizontal so it's out of the way. The bag never needs replacing and only rarely needs to be dropped and the bucket cleaned outó the superfines in the air don't have much volume, just a lot of annoyance.
If you run a blower at low pressure, the motor basically runs at half its max amp rating. For the 3 HP cleaner that's 3-4 KW per hour, and a KW costs me about 8.5Ę. On a 40 hour week, if it ran all day it would cost just over $10, but I only run it when I'm sanding. I use a dust mask also, because my lungs are sensitive, and the dust mask costs about what the electricity does. For the comfort, that's a good price.
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