Dust collection systems

[OFWW]

Seemed to me that there is a lot of black magic thinking about air flow in dust collection systems and no scientific basis used for designs of small shop or home evac systems.

Being that in my trade I am rather familiar with air flow, sizing of ducts, fans, outlets etc. The WYE's and TEE's, the differences between the fittings used, and air measurement, as well as gas and fluid measurements I would have figured that there should be something out there regarding Vacuum systems, but there is very, very little.

Busy Bee's site had a little bit on them, and particle drop out on slopes, using smooth pipe as much as possible, all stuff learned via the college of hard knocks.

Well, the use of a simple manometer is useful for checking designs of air flow, finding restrictions, and a host of other design weaknesses. So I started searching with the word manometer and dust evac systems, etc. Key word being manometer. You can make one very simply with a U-tube, or a gauge or even electronic measurement now a days.

Found this a real joy to my heart, as someone has taken the time to check out the real world. You might find it interesting and also a way of fine tuning what you have an optimizing it.

Acknowledgements My introduction to the problems with dust collection came from Jim Halbert in the mid to late 1990s when he freely shared his knowledge on airflow, cyclone design, and measurement in articles and innumerable forum posts. At the time I was happy with my dust collection system and mostly just glanced at Jim's efforts. I admired and felt sorry for him because many of his posts got attacked and mired in controversy. He consistently told people they believed garbage advertising hype and needed to do some of their own measurement.

Suddenly I landed in the hospital with respiratory problems and my doctors said no more woodworking until I cleaned up my shop. With lots of research including the university where I have taught engineering for over three decades, I kept finding much of the best information on small shop dust collection came from Jim Halbert. By then he had long given up posting, so I did lots of digging through the various woodworking forum archives and finally contacted him directly. He was kind enough to share his dust collection information, design and testing articles and web pages.

Have fun with it, and also a healthier life.

[OFWW]

Here is a link to one of his pages on building your own whole shop cyclone.

There are other pages about this as well as a smaller design IIRC, Full of charts, helps, what not to do and why. A whole lot of reading for someone serious about it.

[-MIKE-]

Great info! Needless to say, I bookmarked it.

[Leon]

Good information!

AND FWIW, mine is a mobile shop, meaning I move all of my "stationary" tools around on mobile bases. I have read about many ways to set a system up to collect from different machines.

YMMV but my approach is simply a 30' flexible hose that runs from my DC overhead to about the center of the shop and then drops down. Because I only use one dust maker at a time I do not need gates, Y's, T's. etc. I simply have a flared plastic end on the end of the 30' flex hose and attachment to each machine is instant. No leaks or things to go wrong. ;~)

[OFWW]

That is basically the way mine is, but the planer and router I ran in the center area, the saws at the door or just outside the door.

I did buy a while back an ceiling filtration system to pick up small stuff that can settle on my stuff, and have the intake facing the corner were sanders, drill press and bandsaw is. Thinking that the air would be drawn to the fan first, some sanders have not vacuum port.

But after reading a bunch of what he says I think I'll put on bigger wheels for some of the stuff to make it easier to roll out, because things like the saws and the joiner fling out high velocity small particles. Working out of a garage seems to have its advantages now, something a closed shop would really need to be cautious about.

I'm wondering now just how many shops have actually blown up as he says because of fine dust and a spark.

[Leon]

On 2/23/2016 12:49 AM, OFWW wrote: Snip

Darn Few if any at all. That discussion has come and gone dozens of times. But there is always the first. ;~)

[Swingman]

Only happens with oak rust ...

[-MIKE-]

My guess would be none. That's one of those things that nobody's ever actually witnessed. :-) It's the old urban myth that happened to a friend of a friend's uncle's brother-in-law's coworker's buddy. The particle concentration has to be so high for that to happen that anyone inside the shop wouldn't be able to see let alone breathe.

Go on Youtube and search for magician's corn starch flame trick or something similar. There's another video of a professor at Texas A&M demonstrating a very small scale grain silo explosion. You can see, albeit very briefly, the amount of corn starch particles needed to create this kind of event. I'll say again, if a shop had that much dust floating around in the air, you wouldn't be able to see across the room or breathe.

[-MIKE-]

Yep! Of course, you'd be dead from that errant nail gun shot from a mile away, first, so it's a moot point.

[Puckdropper]

Leon wrote in news:5NudnUT2o5Z_8lHLnZ2dnUU7-f- [e-mail]:

Experiments by Mythbusters and others have shown the appropriate concentration is so high that you wouldn't be able to see long before you got to the proper air/fuel ratio.

Puckdropper

[dpb]

Problem would not be in general air other than perhaps at a source but theoretically could manage in a collection system with an eneregetic-enough of ignition source. Simple static electricity that has been posited by the use of plastic pipe simply doesn't have that energy without working really, really hard so is essentially impossible.

Spent a long time with pulverized coal transport which is essentially dust collection reversed to be dispersal (inside the boiler, of course :) ) and there it is possible but still rather difficult to achieve the precise conditions (fortunately :) ). Grain dust explosions, on the other hand, are all too easy to manage to create and can do major destruction...

[OFWW]

Two videos of sawdust explosions, one from myth busters, a few news articles from wood mills the blew up, Canada So I guess it is possible. At least in large sites.

[dpb]

On 02/23/2016 8:09 PM, OFWW wrote: ...

"Possible", yes, but what were the ignition sources? _NOT_ static electricity from a DC system.

There _must_ be sufficient energy to meet the ignition point of the mixture, even if it is in a stoichiometric ratio in the combustible/explosive zone. There simply isn't that much energy available in the static discharge of that type.

Every grain dust explosion I'm aware of has been sparked by welding or other construction-related sources or an over-heated bearing or on the rare occasion a spark from a metal strike against something else (it's why besides simply the weight we use aluminum scoops instead of steel) but I think none have been credited to static buildup discharge.

Somewhere I've seen some studies a researcher did that measured the energy of the PVC discharge spark and while it's decently high voltage and zaps pretty good if you're the target, the actually energy dissipated was miniscule; well below the ignition threshold for any solid mixture. Some of the most volatile of hydrocarbons were marginal as I recollect...