PVC ductwork acceptable these days?

[Kevin Crawford]

So I am setting up a new dust collection system for a new shop and the runs a a bit longer than my previous set up where I used metal ducting. When I set up my current runs in metal it was 5 years ago and it seamed there was more concern for grounding pvc ducting and flamibility. It seams like more people are using pvc these days than in the past. Are the concerns not what they used to be? I must admit, spending roughly a third of the cost on pvc for these new runs is appealing.

[Chris Padilla]

Use PVC without fear.

You cannot 'ground' an insulator so don't waste the time and money doing it.

You can get static shocks from PVC but once it gets a bit dusty/dirty, that won't happen any longer.

Finally, the shocks you can get from new, clean PVC do not even remotely have enough energy to ignite anything.

[Keith Outten]

I've used PVC dust collection pipe for 25 years or more without a problem. I have a CNC Router, Laser Engraver, 15" planer and a host of other woodworking machines and never had a problem. PVC is cheap and easy to install and its easy to modify when the need arises.
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[Ole Anderson]

Call me out-of-touch, but I would still opt for steel. But then all of you know that...

[glenn bradley]

These days, those days, any days.

[Jason Beam]

Since i'm a broken record - i really hate that the 'grounding' thing keeps perpetuating ... what Chris Padilla said - you can't ground an insulator so...

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

[Robert Engel]

Yes, the "hazards" of uninsulated pipe have bee thoroughly disproven.
Some people run wires along the pipe and pierce with screws.
The only thing I've done is ground my blast gates because one time I "think" I got a static shock.

[Bill Orbine]

I'm using hdpe triple wall throughout for my DC system and I ran a braided ground wire through everything. The wiring needs to be grounded for it to work effectively. I believe grounding is a necessity. Without it, I would see some dust chips standing erect around the outside of the pipes.....the ground wire killed the effect. It is also suggested that, in addition to running wire inside, you also wrap ground wire around the outside of the pipe for maximum effect but I never got a round tuit! I know of someone who ran DC plastic without ground, got zapped and was nearly knocked out. Not me, no sir!

So plastic pipe is OK as long as you ground the system.....it keeps static electricity from building up,

[eugene thomas]

I use pvc only issue had was when installed cnc it was not happy until I grounded the pipe going to it. but just ran external wire from dust boot to collector and now its happy...

[Chris Padilla]

So plastic pipe is OK as long as you ground the system.....it keeps static electricity from building up,

It works ONLY if you happen to have the metal wire near a spot on the plastic pipe that charge has accumulated but one cannot ground plastic like one can ground metal. Plastic does not have the free electrons that most metals do that allow the flow of charge (a.k.a. current).

[David Ragan]

I run all PVC no ground, no problems

[Jason Beam]

I'm using hdpe triple wall throughout for my DC system and I ran a braided ground wire through everything. The wiring needs to be grounded for it to work effectively. I believe grounding is a necessity. Without it, I would see some dust chips standing erect around the outside of the pipes.....the ground wire killed the effect. It is also suggested that, in addition to running wire inside, you also wrap ground wire around the outside of the pipe for maximum effect but I never got a round tuit! I know of someone who ran DC plastic without ground, got zapped and was nearly knocked out. Not me, no sir!

So plastic pipe is OK as long as you ground the system.....it keeps static electricity from building up,

And this is why the internet keeps this myth alive.

YOU CANNOT GROUND AN INSULATOR - static electricity is named STATIC for a reason - it doesn't move - because it can't, electricity doesn't flow on an insulator.

Please please please, internet, i beg you to stop perpetuating this incorrect information.

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

[Anthony Whitesell]

Use PVC without fear.

You cannot 'ground' an insulator so don't waste the time and money doing it.

You can get static shocks from PVC but once it gets a bit dusty/dirty, that won't happen any longer.

Finally, the shocks you can get from new, clean PVC do not even remotely have enough energy to ignite anything.

The static discharge can have the potential to ignite something, but there isn't anything to ignite.

[Bill Orbine]

And this is why the internet keeps this myth alive.

YOU CANNOT GROUND AN INSULATOR - static electricity is named STATIC for a reason - it doesn't move - because it can't, electricity doesn't flow on an insulator.

Please please please, internet, i beg you to stop perpetuating this incorrect information.

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

Can you help me understand this? This is copied and pasted to here from the link you provided:
If you use PVC the primary issue is to protect yourself from a shock. For this I recommend either a bare grounded wire in the duct, or grounded screws through the pipe spaced every 4 inches. This will reduce the maximum charge build-up by allowing more discharges at lower energies. In a four inch duct, the maximum discharge distance to the bare wire is 4 inches, and the maximum discharge distance to the ground screw is 4.5 inches, so both give approximately equal protection. Because both the wire and screw point have very small radii, they will cause discharges at a much lower charge density than you need for a similar discharge to your finger. The advantage of the screws is that they will not hang up shavings like the wire can. If you are not concerned about receiving shocks, you need not ground the PVC ducts. It is likely that the external ground wire, bare or insulated, or grounded foil wrap is safe in the home shop, but this is problematic if you can generate very large amounts of fine dust.

I'm not trying to start a fight here but I'm not trying to get shocked , either, as I probably didn't state quite clearly in my original post. we're talking a different story of fires and shock....apples and oranges. But either way, my system is set up grounded and it was quite inexpensive and easy to do. Either way, I'm done here. Over and out!

[Jason Beam]

Can you help me understand this? This is copied and pasted to here from the link you provided:
If you use PVC the primary issue is to protect yourself from a shock. For this I recommend either a bare grounded wire in the duct, or grounded screws through the pipe spaced every 4 inches. This will reduce the maximum charge build-up by allowing more discharges at lower energies. In a four inch duct, the maximum discharge distance to the bare wire is 4 inches, and the maximum discharge distance to the ground screw is 4.5 inches, so both give approximately equal protection. Because both the wire and screw point have very small radii, they will cause discharges at a much lower charge density than you need for a similar discharge to your finger. The advantage of the screws is that they will not hang up shavings like the wire can. If you are not concerned about receiving shocks, you need not ground the PVC ducts. It is likely that the external ground wire, bare or insulated, or grounded foil wrap is safe in the home shop, but this is problematic if you can generate very large amounts of fine dust.

That's one point in the article where it's essentially giving in to the idea of "Well if you insist on preventing small shocks, you can kinda do this if it makes you feel better..." -- he also says that just waiting a bit usually solves the static shock problem. Go right ahead and ground your stuff, but don't mistake it for any safety factor - at best, it's a nuisance reduction.

[Wade Lippman]

YOU CANNOT GROUND AN INSULATOR - static electricity is named STATIC for a reason - it doesn't move - because it can't, electricity doesn't flow on an insulator.



So I guess there is no reason for lightning rods...

[Jason Beam]

So I guess there is no reason for lightning rods...

Same reason you don't need airbags while walking ... it's a matter of scale.

[Art Mann]

I use pvc only issue had was when installed cnc it was not happy until I grounded the pipe going to it. but just ran external wire from dust boot to collector and now its happy...

I bet I can guess who the manufacturer is. As far as I'm concerned, that is simply an admission that their controller and/or drive electronics is poorly designed. It was my job for a decade to design under hood computer controls for the automotive industry and that environment is much worse than a wood shop with plastic dust collection pipe. It simply isn't that hard or expensive to design electronics that are immune to such mild static discharge.

[glenn bradley]

I love these threads almost as much as the SS threads...............

Too true. It just gets plain silly. Here, let me stir the pot . . . We get static shocks when we happen to provide the path to ground for the static charge. As long as there is 'anything' that is a more attractive ground path than you are, no problems. The term "grounding" when applied to an insulator is, of course, incorrect but, let's not get pedantic . . . or lets do :D.

In my area, the winters are very dry. You will get shocked off your car door, door knobs, light switch cover plate screws and so forth. In all these cases you happen to be . . . oh, never mind :rolleyes:

[Kevin Crawford]

Well, It seams its as hot a topic as ever. I'm not really concerned about being shocked and I don't think a fire will happen but I think steel pipe might be better for me just because of distance. The longest points of my runs are around 60ft and need to start off at an 8" pipe to the DC. I'm not sure but I think there would be a measurable difference in cfms just because metal ducting can transition from 8"-7"-6"-5"-4" and has longer reducers to ease the transitions. It looks like in PVC, they only have 8"-6"-4" and the reducers are really short.

[Ole Anderson]

Well, It seams its as hot a topic as ever. I'm not really concerned about being shocked and I don't think a fire will happen but I think steel pipe might be better for me just because of distance. The longest points of my runs are around 60ft and need to start off at an 8" pipe to the DC. I'm not sure but I think there would be a measurable difference in cfms just because metal ducting can transition from 8"-7"-6"-5"-4" and has longer reducers to ease the transitions. It looks like in PVC, they only have 8"-6"-4" and the reducers are really short.

That is exactly why you should design your dust collection system around steel duct. And isn't anyone concerned with the possibility of a surprise static shock with your fingers inches from a spinning blade?

[Anthony Whitesell]

That is exactly why you should design your dust collection system around steel duct. And isn't anyone concerned with the possibility of a surprise static shock with your fingers inches from a spinning blade?

But the blades all have guards over them. ;)

[Jason Beam]

That is exactly why you should design your dust collection system around steel duct. And isn't anyone concerned with the possibility of a surprise static shock with your fingers inches from a spinning blade?

In what scenario is this a realistic concern? I genuinely want to know. The best I can imagine is maybe on an over-arm blade guard on the table saw with a PVC 'boom' running across the top of the table - even then, I can't envision a cut that would get my flesh anywhere near the PVC. Where are you guys running your ducts so close to your working envelope that it's even possible to touch them during an operation?

Never mind that for MOST people, that static shock risk is dramatically reduced after the ducts get a little coating of sawdust inside them. Static is built up when dissimilar materials pass over one another - when the coating of sawdust is in place, there's less chance of any build up because it's basically sawdust rubbing on sawdust at that point.

[Bill Richardson]

The simple answer is yes, pvc is fine as long as you're not bothered by the occasional nuisance of the static shock. There is no fire or explosion danger.


The biggest drawback is the expense if you need piping larger than 4". Larger pvc becomes expensive, especially when adding fittings. Metal duct quickly becomes more affordable once you go larger than 4"

[Bob Cooper]

I ran 26 gauge metal because it was cheaper and the flexibility of the ell's was so nice when I needed to make a more gentle radius or when I needed so fork around something. Compare the price of 6" wyes

[Martin Wasner]

The biggest drawback is the expense if you need piping larger than 4". Larger pvc becomes expensive, especially when adding fittings. Metal duct quickly becomes more affordable once you go larger than 4"

This is why I've never understood the fascination with pvc.

[Alan Schaffter]

For those who are saying PVC is more expensive when you get over 4" and that metal flex elbows are nice- you are missing two important points.

First, you are talking about Sched 40 PVC- standard plumbing PVC. That is the wrong stuff. Use the correct PVC, thin-walled ASTM 2729 (also called "S&D", "solid perf", "thin wall sewer and drain," etc.). It is much cheaper (and lighter) than Sched 40 PVC, the green/blue SDR 35, and metal, especially the fittings. You gotta look for this stuff though. You may find 6" S&D fittings in the irrigation section of Lowes, but you won't find 6" S&D pipe there or at HD. You need to go to irrigation pipe suppliers.

As to metal flex elbows- NOT GOOD- introduces resistance and increases SP which you don't want. Likewise, if you are using metal don't use low velocity wyes- again- adds turbulence and resistance.

Finally, you do not need to step down!!!! That is only to balance the system in large HVAC installations like restaurants and larger shops where there is more than one worker and where you may have multiple blast gates open at the same time. Run 6" from DC to machines. Compare the cross sections and flows possible through 4" vs 6" pipe.

[Bob Cooper]

Alan

when I put my system together is was comparing DWV 6" not schedule 40. I'll see if I still have my records of what I learned at the time.

[Alan Schaffter]

Alan

when I put my system together is was comparing DWV 6" not schedule 40. I'll see if I still have my records of what I learned at the time.

Sched 40 is what is used (code) for DWV (drain, waste, vent) plumbing in construction of houses, etc. It is the standard PVC pipe you see in Lowes, HD, etc.

ASTM 2729 has a thinner wall and slightly different O.D. so requires its own fittings. It is not code for house plumbing. Note, the blue/green SDR 35 (also marked ASTM 3034) I mentioned, which you will also often see in big box stores, falls in between Sched 40 and ASTM 2729 as far as wall thickness, weight, and cost- but it has the same OD as ASTM 2729 (smaller than Sched 40). It is all kind of confusing, especially when most places don't know what ASTM 2729 is and call it by different names, some of which I mentioned in my earlier post.