Replies

1. 
   jgaiennie | Feb 26, 2003 01:41pm | #1

   Wanabe,

   I'm not an expert on dust collection piping, but I think you should take a different tac.  Perhaps dispose of what you've done in PVC and start over with metal.

   There's been a lot written about the fire hazards of using PVC for a dust collection system.  Are you aware of this?  Seems sucking dust thru this stuff causes a dangerous buildup of static electricity in about a half an instant.  When a spark then fires, you have a bunch of fine dust suspended in mid air creating an explosion hazard, not to mention that those sparks could be sucked into the pile of dust in your storage container creating a smouldering fire that you may not even know of for hours until it matures into a destructive devilish blaze.

   I've seen photos of PVC systems in service that were fully wrapped with bare ground wire and electrically grounded, minimizing the possibility of a static buildup.  I'd say in the name of safety, you should at least read up on the hazards and inform yourself as to the risks.

   jdg

1. 
   DonC | Feb 26, 2003 09:44pm | #3

   I drill holes for POP rivets every 2 feet in the pipe lines. To these I attached a copper wires on the OUTSIDE to ground. The static charges are eliminated as the material passes the rivets. This solution eliminates all the problems with wires inside and having to "jump" over a open/close gate.

   Any smooth interior will be superior to accordian flex hose.

   Don

1. 
   MHargrove | Feb 27, 2003 01:16am | #4

   Does this approach (wire on the outside, pop-riveted to the PVC), in fact dissipate the static charge?  I'm just about to plumb for dust collection in my new basement workshop, and I've been quite worried about this.  As somebody else mentioned, even the level of static charge buildup from a shop vac is impressive and fast.

1. 
   DonC | Feb 27, 2003 06:46am | #6

   Yo Mark,

   Don't be worried. I would not have posted this as a valid solution unless it truely was a solution. Just think about static charges. If you touched something grounded every 2 feet that you walked, you would never have a static spark.

   If you want to use your shop vac and NEVER get a shock, just drape a thin chain from the handle to the ground. Isn't this what gasoline trucks do??

   Thoughts are never original, it's the applications that counts!

   Yo,

   Don

1. 
   MHargrove | Feb 27, 2003 10:25pm | #7

   I work at a company that flies an earth imaging satellite, so we have, literally, rocket scientists on staff.  I had an email exchange with our chief electronics wizard about static electricity management in PVC, and he was pretty surprised that anybody would even try to use PVC in this manner.  He wasn't convinced than even a large gauge bare wire *inside* the duct would have enough surface area (relative to the PVC) to dissipate the static charge buildup, and was adamant that the outside, riveted version would just not work.  I'll need to talk to him live to make sure he's on the same page as we are -- we don't need to protect flight hardware from static damage, we just need to not have an explosion or fire in the shop.

   Great idea on the shop vac.  I have indeed seen this solution for other applications -- just didn't connect the dots.

   -M.

2. 
   jgaiennie | Feb 27, 2003 05:43am | #5

   Don,

   Thanks for the tip on grounding your pvc pipe.

   I pre piped my shop about 4 years ago with pvc when we were about to close up the walls with rock.  It was sorta a last minute move.  No prior reading.  No forethought.  Just ran a bunch of DWV for a dust collection system.  Now I've tooled up the shop, built a bunch of stuff, and finally got around to buying my dust collection system, and am faced with trying to figure out if my pvc pre-pipe job will work for me in spite of everything I've read.  Whew!  That last sentence winded me.

   Anyway, it's nice to think that I may be able to salvage some of this system by grounding.

   jdg

2. 
   HowardAcheson | Feb 28, 2003 05:10am | #8

   jdg & ALL, I originally replied to your post in an entirely inappropriate manner. For any that saw it before I deleted it, I apoligize. I'd been having a tough day and it was too early for my martini.

   That said,

   FWW ran an article in the last couple of years debunking the perceived danger from static electricity in plastic dust collection piping. One woodworking site even offered a reward for one documented explosion and/or fire resulting from using plastic or PVC piping. There were no takers.

   The writer of that article has his complete research and write up on his website at: http://www.gis.net/~dheaton/woodworking/articles/DC_myths.shtml

   There, now I will get back to my evening martini.

2. 
   BobP02 | Feb 26, 2003 08:47pm | #2

   Wanabe,

   I too have been using the 4" PVC sewer pipe for my dust collection systems. I have used the flex pipe with SMOOTH interior to make gently, sweeping bends if and where practical. This should give less resistance to air flow than a standard 90 degree PVC elbow.

   Regarding static discharge and fire issues...a lot of discussion on many news groups has taken place on this subject. From all that I have read there I have concluded that there is no inherent danger in starting a fire (or explosion) from a stitic discharge within my HOME WORKSHOP system. Emphasis on home workshop as an industrial or commercial environment might not be able to draw the same conclusions. The biggest issue for me has been the static discharge I get when using my shop vac!

   That being said, you absolutely can't go wrong with using metal ducting of the proper gauge and using the nice 90 degree sweeps available for this stuff.

   BobP

3. 
   alanplanesaw | Feb 28, 2003 05:25am | #9

   Howie mentioned an article I was thinking of.  FWW had an article, as I recall a little over a year ago, that I believe said the static build up danger in PVC was related to the length.  Hence, an industrial application, where one would have many many more feet of PVC than in a home, should not be done.  But, he says (again, as I recall -- read it yourself before taking my or anyone's word for it) it might be safe in a small home shop application.

   As I recall, the article was specific about lengths, danger, etc., as it was written by an expert on the subject.

   But, to avoid any danger, or at least minimize as best I could, I used 4" metal duct pipe in my 800 sq ft shop.  As you know, the duct pipe comes in lengths that have be joined the length of one side first.  I put silicone in the slot before I popped them together.  Then when I joined the lengths together, I used sheet metal screws (I may need to take them apart to add a Y or something) to hold them together, then wrapped one layer of duct tape around the joint to seal the joint.

   Has been working successfully for a couple of years so far.

   Alan / planesaw