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Using plastic pipe for sawdust collection?

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  • Using plastic pipe for sawdust collection?

    Several people have told me not to use plastic pipe to connect my sawdust collection system in my home shop because of static sparks that could ignite an explosion. I intend to run the main lines underground under my concrete floor. I think that metal pipe under ground would rust in time and I don't want to have to repair it in the future. What if I would only use plastic underground and metal above? Would the sand and concrete around the plastic pipes ground it well enough to avoid static build-up?

    The plastic pipe is about half the cost compared to metal and would last forever. It goes together easier also. I am about ready to pour my floor so I have to quit pondering and do something. What should I do? Anybody have any first-hand experience? Thanks--Mike.

  • #2
    This was pretty popular when the dust collectors first came out, using PVC trunk lines and gates to each machine. Static build-up was eliminated by running a bare ground wire through the pipe. I never built one, but remember it clearly. Standard wiring connections, to a ground.
    Worked at a place that made IC's with MOSFET's in the mid 70's, very static sensitive. SOP was a ground strap to your wrist, and metal table tops that you plugged it into. So the grounding of the PVC pipe makes sense to me.

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    • #3
      I forgot to mention that I will probably use the Oneida Cyclone 1.5HP collector. Does anyone have any experience or opinion about Oneida? Are they as loud as a regular vacuum? I have sinus allergies to dust and want to make my shop as clean as possible. Will I need a air cleaner besides the cyclone collector? Thanks--Mike.

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      • #4
        this has been discussed often on http://talk.woodmagazine.com/woodtalkindex.html
        The research mentioned shows that there is not a danger of sparks causing an explosion in a home shop and using plastic pipe without the ground wire is fine. If you do a search on that website, you will find a link to some guy who did alot of research on the subject, can't remember his name. When I install a dust collection system this winter, it will be plastic piped.

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        • #5
          Well, I DON't have plastic collection pipe, in fact I don't have a system.

          BUT, my shopvac shocks me nicely through the plastic hose if I pick up a lot of sawdust.

          I understand that the use of plastic is verboten in industrial applications for the spark reason.
          Areas with sawdust are classified "hazardous" under the electrical code, and require different wiring methods than regular areas. Essentially the same requirements apply as for a grain elevator, which as you may remember, used to explode regularly.

          As far as the ground wire in plastic, I have seen that done, and on average it MAY help. It certainly will NOT "ground" the pipe, since the pipe remains non-conductive, and can still create isolated charges on the pipe or the dust. These can then discharge by arcing, or carry a substantial charge to another portion of the equipment by the same action that makes a VandeGraaf generator work.
          I presume you have seen the sort of discharge those devices can create.

          Nothing beats metal pipe, bonded together and grounded as per the industrial requirements.

          And, your pipe in the floor might be a tad hard to clean out if there is a clog.............

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          • #6
            Thanks for all the input guys. I'll check out that website for more info. Does the static build up on the inner surface of the pipe only or can it be drained from the outside with metal shielding or drain wires? My shop has a partial crawl space and I will put in some clean-outs in the ends of the mainlines to be albel to clear clogs. Thanks-Mike.

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            • #7
              As yet there has not been any instances of explosion reported due to static buildup in sawdust collection systems. Plastic pipe in a dust collector can create static, and it can be removed. Do not run the wire inside the pipe this will only cause problems such as clogging, wind it around the outside about 1 twist in 6 to 12 inches and ground it at the end.

              ------------------
              Paul G.
              Paul G.

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              • #8
                Just some thoughts;
                Unless you are going to be making a lot of sawdust, Why not use a large shop vacuum? In my experience they have a lot more suction and are a lot cheaper. I have one mounted to a 55 gallon drum and have made an adapter to use two filters. The two filters let you work longer before they clog up. We are cutting mostly particle board so it is a real fine dust.
                We have mounted an air filter on the ceiling. One of those that are just a box with a fan and a set of filters. This is well worth your time as it cut our dust down to a minimum. We also have a large Jet dust collector---we disconnected it and use the shop vac instead.

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                • #9
                  A shop vac does not have the CFM to remove sawdust from tools like a jointer or planer. The minimum size you need is in the range of 500-600 cfm at the machine for those. A shop vac will pick up just about anything, but it can't handle the volume.

                  Here is a site that has a review of most of the systems as well as some good tips for selecting and installing your unit. http://cnets.net/~eclectic/woodworki...neReviews.html If you get the 0.2 micron filters and install dust chutes on all your equipment, then you probably won't need a ceiling mounted air filter. The air filter also circulates all the dust in the shop to filter it, so if you are standing in the flow path then you are going to breathe in all the dust it is filtering. Several people I have talked to are removing the air filters and just using the dust collector.

                  Mike

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                  • #10
                    Mike,

                    I just thought I would throw in my 2 cents. The problem with static charges lie in their name - static. They do not usually like to move. When you build up a charge on a non- conductor, putting a drain wire near it or against it can only discharge the area of contact. Areas near the ground source will build to a certain point and then discharge (arc) to the ground source. Areas far from the ground will not discharge very well. That's the nature of an insulating material.
                    Folks who work around Electronics and chips will tell you that plastics used in these environments (flooring, shoes, countertops) always have additives to make them conductive so that charges can be bled off to ground.

                    Practically, the plastic pipe probably will work, and from the other posts it seems there is no documented cases of fires. However, static can be dangerous just from the shock. Imagine that you recieve a nasty jolt from you dust collector pipe while operating a power tool - NOT GOOD.

                    I was taught a simple rule when putting things under concrete. Use the best material, oversize it, and put in extra. I personnally use electrical conduit. Thinwall (EMT) strong, galvanized, and cheap (relative to other pipe). Nice smooth bend with large radii are available pre-bent, or mooched from your favorite sparky. These bends are just what you need for material handling systems.

                    Good luck.

                    Alan

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                    • #11
                      Mike,
                      I have as system as you describe but my pipe is over head. I have wire running through all the pvc to ground. The pipe in the earth is a great idea, wish I was able to. It would still need ground because plastic being nonconductive won't get rid of the static to ground.

                      I hope this will help you, Rick.

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                      • #12
                        mikem:
                        Static build up in dust exraction equipment can be extreme. If you are worried about corrosion then use aluminum dryer venting in the concrete and make sure a copper ground wire runs through all plastic piping so the entire system is grounded machine to machine to cyclonic cleaner & dust bins. Do not take the chance - explosions can and do happen when high volumes of air are moved.

                        www.leevalley.com has a book on these systems as well as piping, flexible hose, waste gates, fittings, ground wires, HEPA Dust bags (you may be interested in these) for your Cyclonic cleaner, etc.

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                        • #13
                          True...
                          My previous comment on VandeGraff generators was addressing the fact that

                          the dust being transported rubs the plastic and develops a charge on the plastic, and an opposite charge on the dust.

                          When that dust reaches a conductive item such as the collector bin, or some part of the system, it can give up its charge to the collector, raising the voltage of the conductive item to arbitrarily high levels.

                          If the item is not grounded, the developed charge can arc to some other piece, which if there is flammable dust around, can cause an explosion the same as with flammable vapor.

                          The ground wire in pipe idea is that the dust bits on average will hit the wire and dump the charge before getting to any collector of charge. if you also ground all of the metal parts, then you are pretty safe.

                          I don't know what wrapping wire outside does, might actually have an effect, or not.

                          Metal pipe, grounded, avoids both the charge creation, and the chance of a spark.

                          [This message has been edited by Oso (edited 09-26-2002).]

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                          • #14
                            I was called in to "do something" about the electricity arcing from the plastic pipe to the top of the men's head when they walked under the dust collection system. We used metal mesh like the kind that used to be used on window screens. Wrapped the screen around the pipe - held it on with tye wraps. Attached a wire [the size of wire didn't make any difference]and took the wire to the nearest ground. It worked..
                            Jack

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                            • #15
                              The heat and air guys put metal ductwork under ground all the time so I am going to the HVAC shop this AM and ask them how they do it and whether they have trouble with rust and collapses etc. I thought about aluminum but the regular gauges are so thin that they would likely collapse under vacuum.

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