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  • dust collection run duct

    any problems using ABS black pipe for duct. very small shop puting vac out side using 2" or 3" ?

  • #2
    Re: dust collection run duct

    About the only problem I can see, and I'm NO expert here, is static. I think you would be fine as long as you ran some type of bare ground wire thru it to bleed off the static.
    Brian

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    • #3
      Re: dust collection run duct

      I would use 4" but material wise there is no reason why you couldn't use ABS.
      Teach your kids about taxes..........eat 30 percent of their ice cream.

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      • #4
        Re: dust collection run duct

        I run a carwash and used two vac motors on plywood on top metal trash can use 2" ABS fiting had trouble with can crushing put a 3/8 rod in side reinforce ring . should 4" reduce my cfm and is static a problem ?

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        • #5
          Re: dust collection run duct

          Originally posted by denniswb02 View Post
          I run a carwash and used two vac motors on plywood on top metal trash can use 2" ABS fiting had trouble with can crushing put a 3/8 rod in side reinforce ring . should 4" reduce my cfm and is static a problem ?
          I don't exactly understand what you've done but in general:

          * a larger size of the same "smoothness" of pipe will increase flow compared to a smaller size. You may lose flow velocity in the pipe, though! But if you're using the device as a vacuum, you'll get MORE velocity when you put the vacuum nozzle on.

          * Air flowing in plastic is definitely a static hazard. Because the charge can't conduct anywhere and get out of the plastic pipe (unlike metal), the static voltage can achieve very high levels. At some point you can get enough voltage buildup on the interior surface of your pipe to generate an arc, although it will be a low-current arc. Think of scuffing rubber-soled shoes on the carpet then touching a doorknob. Same idea. Instead of carpet, it's the dust-laden air that's rubbing on the plastic.

          The problem is that the dust is tiny particles which have a very high surface area to volume ratio. It doesn't take much of a spark to light these little particles. This is a huge problem and risk in dust collection in a woodshop, since the wood dust is extremely combustible. It may be less of a problem in a car wash vacuum, but it's a problem nonetheless.

          Black ABS probably has some carbon black in the resin to get the black color, and is possibly a better conductor than white PVC. One should *never* use PVC in an air system.

          If the dust ignites, you have air and combustibles in an enclosed space. It'll explode, and possibly send shards of plastic all over, potentially hurting someone.

          The solution is, as mentiond earlier, to put a coil of bare wire in the duct, so that it makes contact with the plastic many, many places along the length. This provides an escape path for the static charge. You must ground the wire, at both ends if possible.

          Or use galvanized duct, which is what I would personally do.

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          • #6
            Re: dust collection run duct

            Originally posted by Brian Shepley View Post
            About the only problem I can see, and I'm NO expert here, is static. I think you would be fine as long as you ran some type of bare ground wire thru it to bleed off the static.
            Right on, as long as you put some type of bare ground in the pipe you shouldnt have any problems using PVC or ABS.

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            • #7
              Re: dust collection run duct

              Originally posted by Andy_M View Post
              I don't exactly understand what you've done but in general:

              * a larger size of the same "smoothness" of pipe will increase flow compared to a smaller size. You may lose flow velocity in the pipe, though! But if you're using the device as a vacuum, you'll get MORE velocity when you put the vacuum nozzle on.

              * Air flowing in plastic is definitely a static hazard. Because the charge can't conduct anywhere and get out of the plastic pipe (unlike metal), the static voltage can achieve very high levels. At some point you can get enough voltage buildup on the interior surface of your pipe to generate an arc, although it will be a low-current arc. Think of scuffing rubber-soled shoes on the carpet then touching a doorknob. Same idea. Instead of carpet, it's the dust-laden air that's rubbing on the plastic.

              The problem is that the dust is tiny particles which have a very high surface area to volume ratio. It doesn't take much of a spark to light these little particles. This is a huge problem and risk in dust collection in a woodshop, since the wood dust is extremely combustible. It may be less of a problem in a car wash vacuum, but it's a problem nonetheless.

              Black ABS probably has some carbon black in the resin to get the black color, and is possibly a better conductor than white PVC. One should *never* use PVC in an air system.

              If the dust ignites, you have air and combustibles in an enclosed space. It'll explode, and possibly send shards of plastic all over, potentially hurting someone.

              The solution is, as mentiond earlier, to put a coil of bare wire in the duct, so that it makes contact with the plastic many, many places along the length. This provides an escape path for the static charge. You must ground the wire, at both ends if possible.

              Or use galvanized duct, which is what I would personally do.
              What about when its used for HVAC under basement slabs?

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              • #8
                Re: dust collection run duct

                Great question and I don't know the answer. Since there shouldn't be alot of dust in an HVAC run, compared to a dust collection run, I would guess it's not so much of a problem. Also, the flow velocity is low in HVAC compared to dust collection. so, less static buildup. But one shouldn't guess, one should check with the building inspector.

                I should have qualified my comments to dust collection and/or shop compressed air.

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                • #9
                  Re: dust collection run duct

                  For a good discussion on static in PVC dust piping, you may want to read the following. It gets a bit technical, but does make some very good points about the futility of trying to "ground" a non-conductive material to remove static. It is rather long, so you may want to skip to the end under "myths", and then go back and read the info concerning any you are interested in.

                  http://home.comcast.net/~rodec/woodw.../DC_myths.html

                  Another case where what seems so "logical" just doesn't hold up to scientific scrutiny. Dust explosions in a home sized dust collection could be a topic for Adam and Jamie: the Mythbusters.

                  Go
                  Last edited by Gofor; 02-17-2010, 08:43 PM.
                  Practicing at practical wood working

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                  • #10
                    Re: dust collection run duct

                    I know that this issue has been a pretty hotly debated one - i.e., is the static issue real or not. I hadn't previously seen the link that you provided and agree that it presents a compelling case for static-caused explosion danger not being a valid concern. I'm still not totally convinced but he does make a good case. He does talk about leakage current but doesn't really address surface creepage as a mechanism for electrons to get to the ground wire. There's other things mentioned there that could bear some loking into as well. Still, other internet searches seem to also point to the fears of PVC in dust collection as being well overblown. So I will accept that my cautions may well be overly conservative.

                    Personally, I would still use metal ducts. But then again, I overkill everything.

                    I should add, though, that even while we're talking dust collection here - I am fully convinced that one should not use plastic for compressed air distribution.
                    Last edited by Andy_M; 02-19-2010, 03:54 PM.

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                    • #11
                      Re: dust collection run duct

                      Originally posted by Andy_M View Post
                      .................................................. ...
                      I should add, though, that even while we're talking dust collection here - I am fully convinced that one should not use plastic for compressed air distribution.
                      Not only you but I doubt if you will find a plastics manufacturer that would recommend it either.
                      Teach your kids about taxes..........eat 30 percent of their ice cream.

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