PVC for dust collection, is it safe?

[jtpr]

I asked a long time ago about duct work for DC in my shop, 2 years later I'= m finally ready to do it. I have a 1.5hp single stage collector and I want= to get the 4" hoses off the floor. I would really like to use 4" PVC to d= o this as it is a whole lot easier, accessible, and cheaper. But what abou= t static? Is it really that unsafe? Can it be grounded? This is a small = shop, 20x20 and I will probably just be going to my table saw and planer to= start. If the PVC is really not safe, then what is wrong with the 30 gaug= e metal stuff at HD? I can't believe I have the horsepower in this machine= to buckle it, but maybe I'm wrong. It's just that going to Woodcraft for = duct work is VERY expensive, and ordering online is a PITA whenever I need = something. =20

Thanks again for the input.

-Jim

[dpb]

On 7/25/2012 10:54 AM, jtpr wrote: ...

4" PVC to do this as it is a whole lot easier, accessible, and cheaper. But what about static? Is it really that unsafe? Can it be grounded?

...

There is no evidence whatever that any small diameter dust collection system has had an explosion or fire sparked by static discharge in plastic.

It _will_ shock on occasion like the olden days of wool carpets and dry indoor conditions.

You can attempt to minimize that by wrapping w/ wire and grounding but since the material is nonconductive it's of marginal benefit.

The biggest pita w/ it is twofold --

1) The fittings for 4" dust collection aren't the same size as Sch 40 fittings so you have to adapt everything, and

2) It does and will collect from static charge.

But, there are thousands of applications and I've used drain/waste PVC w/ the molded-in fittings for the main laterals here as it's lighter/cheaper and the 10-ft joints are convenient in small shop areas.

I didn't bother to glue joints, they fit well enough to not leak significantly and can rearrange if desired/needed.

BTW, be sure you use sweeps and larger radius fittings rather than ordinary tight elbows for less pressure drop and fewer hangups. Also keep the amount of flex hose to the bare minimum possible--it's the biggest sucker-upper of airflow you can have other than a block gate.

OBTW -- on the 30-ga HVAC stuff--I've not tried it on a 2 hp collector but it will all depend on what pressure drop your fan will pull. At worst buy a section, hook it up to the inlet directly and do a block test and see if you can collapse it or not.

--

[Puckdropper]

dpb wrote in news:jup5mu$ef8$ [e-mail]:

*snip*

If you're worried about collapsing, a simple pressure relief damper can be installed at the end of the run. All it is is basically a damper that can turn freely that is weighted at one end. In normal operation, the damper stays closed for maximum draw from the outlets. In a clogged/choked condition, the damper opens to take the pressure off the pipe.

Puckdropper

[dpb]

...

Oh, gee, and take all the suspense out??? :)

--

[-MIKE-]

You'll be fine as long as you never run any oak saw dust through it. Oak rust will rot that mofo from the inside out and the resulting explosion will send shrapnel up to a mile, killing everyone in sight.

[Swingman]

It will also negate your homeowner's insurance, and turn all your cherry brown ...

[tiredofspam]

Geez you're killing me... :-)

[CW]

You'll be fine as long as you never run any oak saw dust through it. Oak rust will rot that mofo from the inside out and the resulting explosion will send shrapnel up to a mile, killing everyone in sight. ================================================================== Except Rambo.

[FrozenNorth]

and Chuck Norris. :-)

[Larry Jaques]

That goes without saying. Also, it won't harm Superman or the Terminator, either in governator form or in mufti.

-- In the depth of winter, I finally learned that within me there lay an invincible summer. -- Albert Camus

[Puckdropper]

-MIKE- wrote in news:jupl0r$luv$1 @speranza.aioe.org:

Who's sight? If he just closes his eyes immediately after the oak rust explosion, will everyone be safe?

Save us, man! Close your eyes!

Puckdropper

[krw]

I found some adapters (Rockler) that adapt drainage (schedule 20?) PVC to dust collector stuff. The problem I have is that I've found that 4" dust collection hardware doesn't fit 4" dust collection hardware. Indeed, different tools have different sized ports. Grr.

[RonB]

You just had to do that didn't you Mike. We came this far without any crazy crash, burn and obliterated statements - then this.

I know - the devil made you......

Jeeeeesssshhhhh!

RonB

[-MIKE-]

crash, burn and obliterated statements - then this.

Did you know SawStop was designed totally on Google Sketchup, the best CAD program in the world? :-)

[Joe]

After a lot of reading and encountering the same comments on static discharge - pro and con - as you have, I went with 4" DWV and haven't noticed any static at all. My environment is hot and humid most of of the year though, which may account for it. To second the comments already posted, a chip collector is wonderful since it keeps the nasties out of the fan and bags. I ran across plans somewhere for a labyrinthine box with inlet and outlet high on the sides. It's a simple ply box with a vertical divider coming down from the top. I caulked the seams and added a short piece of 4" PVC on the bottom for emptying with a cap just stuck on it. It's hung on the wall with french cleats in an adjacent room next to the DC. About an inch a year of sawdust and dirt makes it to the bag. Only thing I'd change is to hang it higher so it would be easier to empty. I use 2 45s instead of long-sweep 90s since they were cheaper at the time and provide as big a curve as you want.

-J

[Dr. Deb]

Mythbusters did a show on trying to get enough static electricty off a piecss of PVC pipe to cause an explosion. The listed it as "Thoroughly Busted."

Deb

[Leon]

I would have thought the PVC would have only let off a spark rather than being thoroughly busted.

[dpb]

On 7/26/2012 12:16 PM, Mike Marlow wrote: ...

The biggest problem in woodshop dust explosion (getting one, that is) is that the particle sizes are far too large if there is enough mass and it's essentially impossible to generate enough mass by sanding to reach the necessary stoichiometry (concentration). I estimated once that to reach the level w/ sanding a 1-ft square board in a very small 250 cfm system it would require something like removing almost 3/16" of material a minute over the entire surface to reach the 0.003 lb/cuft estimated by US FPL as the lower critical concentration for an explosion.

Then in PVC, while it builds a great charge, owing to it being an insulator it is virtually impossible to get an actual discharge spark of any energy content to speak of as only a very small portion of the charge will travel to the discharge point. This is different than a conductive surface that allows for charge transport through the material.

So you can get the annoying static charge that makes hair stand on end and collects dust, etc., etc., etc., but can't get an energetic charge to light it off even if could get the dust concentration.

Where there's more hazard is in the collections but it's not explosion it's a smoldering spark that finally bursts to flame if a metal chunk hits a metal fan and makes a hot flying chunk...

I came close in the base of the PM66 once when hit a wood screw and it did the nasty...

--

[Larry Jaques]

I didn't think PVC pipe -wore- bras.

-- It takes as much energy to wish as to plan. --Eleanor Roosevelt