PVC for dust collection
Plastic pipe systems are not designed for dust collection use. A necessary diversity of fittings to meet design requirement does not exist. Also, plastic pipe elbows have a very short radius and plastic tee fittings are improper for dust removal. It is these types of problems that lead to an inefficient dust collection system.
With a metal dust collection piping system, static electrically won't develop. Elbows and other various fittings are properly designed for conveying dust. The diversity of fittings and accessories will enable you to meet design requirements.
I have found no problems using schedule 40 PVC. You do need to run a ground wire to each machine. As far as elbows are concerned, you can use electrical sweeps, which ease the bends. Also, don't use tees - use Y fittings.
I used plastic in my first shop. The static electric buildup was amazing. I tried to control it with ground wires, but still had problems. Don't take a chance on a dust explosion - use metal. Commercial heating contractors often stock the spiral duct and fittings since they are used in big buildings for air handling.
The National Fire Protection Agency recommends non-combustible ducting when conveying combustible material. As we know, wood dust is combustible, as well as PVC pipe, never mind the static buildup, which is a source of ignition.
When we create a duct system, the interior should be as obstruction-free as possible. A copper wire will snag chips and curls. In addition, many extraction systems are abrasive, such as the conveying of hardwood chips. This material will wear the copper wire.
When we had a PVC system in our shop, I had a chance to discuss the plastic pipe/static situation with an electrical engineer well-versed in industrial issues. According to him, there is virtually no way to protect a plastic based system. The static builds on the surfaces (inside or out) of the pipe and nothing but a continuous metallic ground (more like a coating than a wire) inside the pipe would mitigate the static buildup. He convinced me to get rid of the plastic and redo our system with metal pipe and fittings.
While removing the plastic (prior to a metal install) on a Monday after a non-working weekend, I noticed that the pipe still held a charge from the previous Friday's work. As a precaution I put on light duty rubber gloves. I got zapped right through the gloves by the static discharge from a length of pipe connected to the planer, which had been working hard the previous week. A few minutes later I picked up a piece of pipe that had also been connected to the planer and watched as a large spark arced from the pipe to my chest. These shocks were not life-threatening, as the discharge was mostly voltage with little amperage. That said, they made me painfully aware of the potential for static build-up.
You may get away with a plastic system for years, but some day when you are collecting large quantities of fine dust through your new wide-belt sander, disaster may strike. I'd never consider using anything but metal pipe for dust collection.
I have PVC in my shop and after a short while the static problem has gone completely away. I attribute this to dust/tracking within the system. It has worked out very well for me, is easily revamped into additional configurations as my shop has grown, and was readily available to me. I have no fear of an explosion ever occurring.
From contributor M:
Plastic pipe does indeed present a considerable risk. You may not have had any problems yet and you may know folks who have plastic systems that have not had problems. Simply because you have not had an explosion doesnít mean that it canít happen.
Though dust related explosions may not be an every day occurrence, they are not rare and the use of plastic pipe in a system that generates large amounts of fine flammable dust/particles is asking for a disaster.
Iíve seen first-hand evidence of what static discharge in dust collection systems can do. Practically speaking, it cannot be eliminated in plastic systems. When it discharges, it can ignite the dust in the system with explosive force. Iíve also spoken with experts in all phases of woodworking plant management and dust collection system design. They all condemn the use of plastic pipe and fittings for transport or collection of wood dust.
Dust explosions do occur in large commercial systems but there is a critical minimum size for an in cloud discharge. Lightning-like discharges in the dust cloud itself can ignite dust, but do not occur in dust clouds smaller than about 3 meters (10 ft) in diameter (Boschung, et al, p. 309).
From contributor M:
The reference you point to is clearly talking about the possibility of dust explosions in the ďhome shopĒ. We're not talking about home shops on this forum. The recommendations I've given and those from other industry experts are to avoid practices that can be dangerous.
I have personally experienced the dramatic effects of static discharge in pvc systems. I also have very reliable information of a dust system explosion, caused by static discharge, that caused a devastating fire in a commercial woodworking shop.
Frankly, I just donít understand the zealous defense of pvc pipe dust systems. Itís potentially dangerous, and itís only marginally cheaper and easier to install than standard metal pipe and fittings. Iím going to use pvc for plumbing and metal for dust system construction.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
Comment from contributor R:
I had originally set up my small wood shop (14 x 20) with 3" PVC for my dust collection system because of the ease of working with the medium. I used the curved Y joints instead of 'T' joints eliminated any buildup in the bends as I routed it to the different machines. Plus being able to form and directly glue the blast gates to the pipe for a solid feel when opening was great.
Once I started reading all the adverse effects of the PVC in relation to static electricity I began to worry. As a test, I drilled the PVC pipe every 12" and screwed a 3/4" stainless sheet metal screw into the pipe and extending about 1/2' into the flow area. Each of these screws were then wired together and tied to the nearest electrical box for ground.
I haven't had any zaps while working with the system since. Again my shop is only 14 x 20 with 4 inputs to the 2hp system. Most of the collection is large particles from the table saw, router, combination saw and lathe. I use it to vacuum the floor as well.
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