DC ducts - 4" or 6"

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referencing.. http://cnets.net/~eclectic/woodworking/cyclone/Ducting.cfm#Ducting%20Introduction
I have the Jet cartridge 1.5hp unit; rated 1100cfm
Based on the URL, I plan to use sewer & drain pipe. I will use wye's and short (1-2') flex hose.
Should I try 6" duct? If I read this correctly, he is saying that no reduction should be done.. so I really have to convert all dust ports to 6". That's possible for my TS, SCMS, and jointer, but not very practical for my planer, BS, and DP.
I have a 23x18 shop. Planning to place DC in corner.. and duct along the 23' wall, with wye's off to a TS/Jointer/Planer/BS area.. (closest to DC), SCMS area, and DP area
DC | BS \ | \ | J/TS__ / P | | | SCMS_/ | | | | DP_ /
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nospam snipped-for-privacy@mesanetworks.net thus spake:

IMHO, 6" is probably a big for a 1.5HP unit - real world CFM is probably lower than advertised - 5" would be a better match. Velocity needs to kept up, or the material falls out of suspension. Metal ducting is probably more widely available at 5" and requires no grounding wires. I believe the no reduction rule applies to runs, not connection branches - but make up air has to come from somewhere to keep the velocity up. In consideration of the economics of it all, I believe short 4" runs to equipment would be fine. Various leakages would make up some of the difference - or an inlet relief flap at the end of the run.
JMHO however,
Greg G.
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Greg G. wrote:

Why would you need to ground the pipe?
UA100
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Unisaw A100 wrote:

Dust can be explosive.
--
Mortimer Schnerd, RN

snipped-for-privacy@BARFcarolina.rr.com
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I know we asked the question at the end of last year "does anyone have first hand experience with a wood dust explosion" and the answer was "NO". So maybe it's that time of year to ask it again. Cheers, JG
"Mortimer Schnerd, RN" wrote:

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Mortimer Schnerd, RN wrote:

Prove it.
UA100
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Good grief! Almost any fine organic (and some metal) powder can be explosive (or maybe just burn fast, depending on your definition of explosion). No one needs to prove it, it's been demonstrated time after time in class rooms, at safety shows, on television, etc.
However, the stuff that ends up in my nose when sawing wood, is, I think, way to coarse to explode. It has to so fine that it almost will not settle but just stays in the air. I can't imagine anyone working in such conditions. And he/she would need to worry much more about their lungs and eyes.
I have no idea if wood dust has ever caused an explosion in a wood shop, but fine dust can be explosive.
Unisaw A100 wrote:

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George E. Cawthon wrote:

A'yup. And my Grandma's face burst into flames when she was flying jets over the Sinai.
Sorry, you'da had to been here for more than the last week to be getting that one George.
UA100
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Been reading this newsgroup for a long time, but selectively. Don't remember Grandma's face. Cheers.
Unisaw A100 wrote:

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Well, a long, long time ago, back when Israel owned the Sinai Peninsula and Egypt wanted it back, an old granny was flying peace keeping missions in A4s along the Delta line when she switched to pure oxygen. Nowadays, aging pilots just don't wear makeup, hairspray or greasy lipstick when using pure oxygen, face-fires ain't a pretty sight.
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My insurance seem to think that it is - as do the authorities in Europe after a number of injuries in recent years in factories. The scenario seems to run something like this - spark generated in the ductwork (e.g. from a sander, grit from timber, lost carbide tooth, etc.), spark arrives in collector and smoulders in waste, someone knocks out the dust sack (creating a stochiastically viable mixture of air and fine wood dust), air/dust mixture ignites and causes a small explosion which blows the bag off the extractor, the force of this explosion is not enough to harm anyone but dislodges all the dust trapped on beams, tops of machines, etc for many years past, this is turn generates a much larger volume of air/dust which in turn is ignited by the initial explosion..... This can happen in small shops, too, but is probably much more of a problem in commercial environments.
Personally, I'm not so sure any more about the static sparking theory (and if you follow one of the links of Bill Pentz's site you'll find a properly researched paper on the subject by an academic which says just that), but I've heard enough foreign objects striking the ductwork to believe that a fire or explosion in a collector is possible. Never had one myself, but last year we did have a dust sack which had been removed at the end of the working day catch fire.... (luckily outside of the shop)
I'd still tend to earth galv. steel trunking in the same way as I earth strapped our steel roof trusses, gives lightening or shorts and easier journey to earth.
Scrit

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Unisaw A100 thus spake:

Oh, God - here we go again... Convention? Elimination of static buildup?
Just ask a midwesterner about silo explosions. Far courser material, yet it CAN explode. Have I ever seen it? No - maybe 'cause they are grounded by convention... <g>
Greg G.
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Yep, here we go again. A) Silo explosions are not caused by static, but usually by an electrical spark on faulty equipment. The energy in a spark is far greater than energy produced by a static discharge; it also is of longer duration B) the material that causes silo explosion is not far courser material, it is actually very fine, very concentrated dust produced as a result of moving very many TONS of material in a short period of time.
The archives should provide sufficient information to rehash this for the curious.
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Mark & Juanita thus spake:

Probably picking nits here... Although I understand how you came to these conclusions, for the record, I never directly stated that static caused silo explosions. I used that as a rational for why dust collectors are often grounded - in a different paragraph. But by the same token, it could happen. A spark is a spark. Lightning, electrical equipment, sparking contacts in switches just thrown are all potential sources of ignition. This is why they have specialized equipment that is sealed to prevent this from happening. A Kettering ignition system has a fairly short spark duration - but it ignites a highly pressurized cylinder full of atomized fuel - every time. (Hopefully...)
I also never said course material was the fuel for the explosion. Of course it is finely atomized dust particles. But the average bystander sees corn, or wheat - larger material than sawdust - which, incidentally, contains many fine dust-like particles itself. As anyone who has ever used a dust collector can attest, the friction of sawdust moving through a plastic pipe generates static.
With this said, a friend has a picture frame shop. When he installed his dust evacuation system, the inspectors required it to be grounded. Why? I don't know. Probably the same reason they don't allow PVC air lines. The chances are 1 in 10,000, but there apparently IS a chance of something untoward happening. Have I ever seen it or heard a substantiated case of it happening? No!
I would say, that for myself, a couple of dollars worth of wire is cheap insurance, and of benefit if only to eliminate that annoying static shock from touching an ungrounded, static charged thingamabob in the DC's path.
Just for the record. ;-)
Greg G.
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For all you disbelievers that dust cant explode I've had the unfotunate experience of seeing 2 of our local firemen killed in an explosion at our local lumber yard. Sure the fire started in silo but the silo contained nothing more than sawdust , A short in the dust collecter motor sent a spark through the duct system that started what seemed to be a harmless fire, when the firefighters arrived they went about putting out the fire as a routine call, moments later the silo exploded and sent pieces of the silo over a mile away.The 2 firemen killed were spraying water down the top of the silo, the explosion was caused by a void ( air pocket) in the material in the silo, when it was saturated with water it became heavy and fell to the bottom, the dust cloud that was created when the material hit the bottom had enough power that when it exploded it sent pieces of the silo over a mile away. needless to say what happened to the 2 men that were looking down the throat of the silo.
Greg G. says...

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just for the record; we aren't all as skeptical is Unisaw100... I'm with you, D&C.
dave
DAN & CINDY wrote:

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Well, there goes any credibility D&C had....
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@woh.rr.com says...

A) Nobody is disputing the fact that dust can explode; there is both empirical and anecdotal evidence to demonstrate this. However, for dust to explode, it must be in sufficient concentration and a proper ignition source must exist to transfer energy into the dust cloud to start combustion. In the example you cite, the ignition source was a sustained fire, the dust concentration was caused by a large quantity of existing fine dust in a silo that was storing said material.
What is in dispute is 1) Whether it is even remotely possible to entrain sufficient dust in a home workshop dust collection system for sufficient time, in sufficient concentration to be an explosion hazard and 2) Whether a static discharge in a plastic duct will occur across that concentration of dust, and whether there is sufficient energy in that spark to start combustion. IIRC, someone posted a number several years ago when this subject came up regarding the combustion temperature required to ignite saw dust; the number was significantly higher than what one could obtain from a simple static spark -- you are much more vulnerable to glowing pieces of metal that could enter the DC system from sources such as accidentally grinding metal on one of your tools.
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Greg G. wrote:

I'm a midwesterner. Trouble is I don't use my shop for a silo.

It can? Have you proof? Can you refer me to someone whose shop has *blowed up* onna 'count of PVC pipe and their dust collector? Can you refer me to a fire department,,, OK, I think you know I know you can't.

Uh, huh. As I thought.
UA100
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Unisaw A100 said:

Hmmm... folks are getting mighty testy over this one...
I could care less if you ground your DC or not, I'm not twisting any arms - just playing devil's advocate. So don't take it personally.
But, as stated in a previous post:
... a friend has a picture frame shop. When he installed his dust evacuation system, the inspectors required it to be grounded.
Why? I don't know. Probably the same reason they don't allow PVC air lines. The chances are 1 in 10,000, but there apparently IS a chance of something untoward happening. Have I ever seen it or heard a substantiated case of it happening? No!
I would say, that for myself, a couple of dollars worth of wire is cheap insurance, and of benefit if only to eliminate that annoying static shock from touching an ungrounded, static charged thingamabob in the DC's path.
Just for the record. ;-)
Greg G.
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