# Sometimes thinking just gets me into trouble



## Sawdust2012 (Sep 17, 2013)

And this may be another case of that, but…I see 1 micron filters advertised in a range of $115 to $350. These make sense to me , as I want to avoid the "dust recirc pump". HOWEVER, if I use a cyclone seperator to remove 99% of the junk from the air! there isn't all that much headed to the filter. Many have posted here that they only get a teaspoon or two in their filters. That being the case, why do I need a huge filter? I understand the filter area / resistance equation, but if I am figuring the cubic in displacement of a large Diesel engine x rpm correctly, there is a pretty large volume of air traveling through those filters. Why can't I secure a heavy equipment filter to the exhaust end of my bower, or, for that matter, a series of a few automotive filters? This would be considerably cheaper. I may be missing something, so someone please educate me.


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## crank49 (Apr 7, 2010)

Cyclones by themselves, unless they are super high efficiency models, are worthless for capturing any more dust than a 30 micron bag filter. Just because a cyclone manufacturer puts words like "High Efficiency" on their advertizing is not an indication of true high efficiency from a technical point of view. A true high efficiency cyclone, able to capture 99.997% of particles larger than 0.3 micron would have a pressure drop of well over 20" static pressure. That's more pressure than most small collector fans can generate. That is why most home shop cyclones are of the medium efficiency design and have a filter cartridge on their exhaust.

As far as bag filters being a recirculating dust pumps, that's more marketing hype coming from certain cyclone manufacturers. Any filter, bag, cartridge, cyclone or even electrostatic recipitators or wet scrubbers will capture some of the fine dust; some devices just do a better job of it than others.

Truly high efficiency cyclones exist and are usually only justified if there is some reason a cartridge filter won't work. Like an application with super fine sticky particulate, or heat, sparks or flame that would burn up a filter. The reason they are not common;y used is cost of operation.

To get the very high pressures required takes a lot of horsepower. To take a 2 hp fan that can generate 12" static pressure and speed it up to where it would produce the required 24" of static pressure at the same CFM would require an 8 hp motor. It's simply more economically feasable to live with the lower pressure and use a filter cartridge.

There are some jocks on here who have done just what you you are suggesting and there are filters used by large trucks that are almost the same as the often suggested Wynn cartridge. I would rather have a truck air filter than a bag filter and a pre filter consisting of a trash can with two duct/hose connectors on the lid.


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## timbertailor (Jul 2, 2014)

The filters are expensive because of their construction. They are made to handle high flow rates without clogging as quickly as a smaller filter with less flow. As simple as that.

Quality filtration is a health issue and blowing fine particles back into the shop due to inadequate filtration is more dangerous that going without dust collection at all.


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## bigblockyeti (Sep 9, 2013)

+1 to what crank49 explained. Regarding the use of filters used on large diesels, they have the ability to draw a much greater vacuum than a centrifugal fan you'd find in a cyclone or any other dust collector for that matter. As the filters get dirty, the engines lose power, if changed on an appropriate PM schedule, this doesn't amount to much on a percentage basis, but given the vacuum pressure available from a dust collector the airflow reduction would be very substantial.


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## intelligen (Dec 28, 2009)

As crank mentioned, you should be looking at better filtration than 1 micron. A cyclone and high-efficiency filter are complementary components in a dust collection system. A cyclone does separate most of the larger particles from the air but its ability to capture small particles is limited (at least, on any scale that any of us can likely afford). A high-efficiency filter can capture sub-micron particles, but without a pre-separator it will load and clog much more quickly. Several people here have mentioned that they installed new or used truck filters on their dust collection systems and they worked fine, but it wasn't clear to me what level of filtration they were actually getting since the filter ratings used different certification criteria.

You didn't mention whether you wear a respirator, but I wouldn't even begin worrying about fine dust filtration until after you've spent $30-$50 on a good respirator and a set of P100 cartridges. You can get pretty decent disposable valved P100 masks, but they don't get as good a seal, and even the P95 ones (which have slightly worse filtration) are not nearly as cost-effective as a respirator with replaceable filters.


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## wormil (Nov 19, 2011)

> Quality filtration is a health issue and blowing fine particles back into the shop due to inadequate filtration is more dangerous that going without dust collection at all.
> 
> - timbertailor


This is a frequently quoted Bill Pentz line that doesn't make sense. No filtration where you put 100% of the particles into the air is safer than inadequate filtration which removes 98% of the particles from the air? No it isn't. Even if the micron particles were the only danger (which they are not) and the "inadequate" filtration removed none of those particles (which it does), then at worst the "inadequate" filtration would break even with no filtration.


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## JADobson (Aug 14, 2012)

> Quality filtration is a health issue and blowing fine particles back into the shop due to inadequate filtration is more dangerous that going without dust collection at all.
> 
> - timbertailor
> 
> ...


Good point. Logic, some people got it, others…


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## timbertailor (Jul 2, 2014)

> Quality filtration is a health issue and blowing fine particles back into the shop due to inadequate filtration is more dangerous that going without dust collection at all.
> 
> - timbertailor
> 
> ...


The repeated release is the danger. The flow rates of dust collectors is in the neighborhood of 400CFM on average. If your garage is only. 20'x20'x10', that is 4000ft3. Every ten minutes, almost all the air in the room has been replace with air coming directly from the dust collector! THAT is the math for those who wish to ponder it.


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## wormil (Nov 19, 2011)

> The repeated release is the danger.
> - timbertailor


Still ignores larger particles and assumes the filter captures none of the smaller particles. Your math is telling us the theoretical rate at which air is cycled through the filter, nothing else. When you say one thing is worse than another, you need data collection and a control. At the very minimum you need measurements showing that air quality is worse with an "inadequate" dust collector than none at all, and should have some health statistics showing that people working in a no DC environment suffer fewer breathing related issues. To my knowledge not even Bill Pentz has published data to that effect though he still claims none is better than imperfect.


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## wseand (Jan 27, 2010)

I use my lungs to filter the air, works good. ~


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## bigblockyeti (Sep 9, 2013)

Many people use that method, helps keep our insurance co-pays nice and high.


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## intelligen (Dec 28, 2009)

> Quality filtration is a health issue and blowing fine particles back into the shop due to inadequate filtration is more dangerous that going without dust collection at all.
> 
> - timbertailor
> 
> ...


Isn't it obvious? If you have no dust collection at all, then the big particles will collect on your lungs and improve their efficiency at blocking the smaller particles, similar to how loading works on your dust collector filter, whether it's a canister or bag. If you filter all the big particles out of the air, then the smaller particles just go right into your lungs, which is way worse because…uhh…because.



> To my knowledge not even Bill Pentz has published data to that effect though he still claims none is better than imperfect.
> 
> - Rick M.


Why is it that everybody has to try to poke holes in Bill Pentz's unsupported, non-peer-reviewed claims on the Internet? What's next, a congressional hearing and a scientific study debunking Dr. Oz's miracle supplements, anti-aging creams, and magic beans?


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## wormil (Nov 19, 2011)

Low hanging fruit I guess, lol. No, it's just I've seen that phrase turn up in several forums recently, unchallenged. People embrace it as if it were completely intuitive that no DC is better than imperfect DC. I challenged it on another forum but my post was deleted.


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## Sawdust2012 (Sep 17, 2013)

If we are going to dismiss opinions merely for lack of evidence or coroboration, shouldn't we all get our Freon and aerosol cans back?


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## intelligen (Dec 28, 2009)

In case it isn't obvious, my previous post is 100% sarcastic.

Kidding aside, the only semi-legitimate reasoning I've heard before behind the "no filtration is better than inadequate filtration" line is that you'll be more inclined to wear a respirator if you can see the dust in the air, whereas you may give yourself a false sense of safety when the larger particles are filtered out but the air is still loaded with fine particles. To some degree, I think this is true, because I read all the time about various canister filters (Wynn, truck filters, etc.) but nobody ever emphasizes that they also wear a respirator. Maybe they do, maybe they don't, but I think most people assume since the respirator often isn't mentioned (or is mentioned as an afterthought), the sub-micron filter makes a respirator unnecessary when, in fact, it should be considered absolutely necessary in most situations.

The lesson here is that you should always wear a well-fitted respirator with P100 cartridges, and whatever dust collection or filtration you do on top of that at the tool is for the benefit of finishing or keeping your shop clean.


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## Dal300 (Aug 4, 2011)

With my breathing problems I am not able to wear a respirator for more than about 45 seconds.

My method may not be the best, but it's what I have and I built it myself. HF chip blower, 4" tube for 10' in a straight line to the table saw, 2'-4" line to the planer, 5'-2" line to the band saw.
I also have a vacuum port on the floor to sweep floor junk into.
All have a method of closing them off.
The filter is one built for a commercial application, sub .03 micron capacity, and I have a 42 gallon rubber made with a home made chip separator.

It seems to work well, but I thought I needed something else so I used a 3/4HP 14" impeller squirrel cage blower with multiple MERV 15 furnace filters on both intakes.

Even as well as the collector works, I have to replace the dust filters every month as they will be almost plugged.
BTW: you can tell when they are getting full because the motor and impeller have different sounds.


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## intelligen (Dec 28, 2009)

> With my breathing problems I am not able to wear a respirator for more than about 45 seconds.


Sorry to hear that. It sounds like you're happy with your current setup but if you or anyone else with a similar condition (or a beard which prevents a normal respirator from making a proper seal), there are also continuous flow respirators. One of the turners from my woodworking club recently recommended a model that has the air circulation fan in a fanny pack vs. the type that has the fan/motor mounted in the top of the mask.


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