So I guess there is no reason for lightning rods...Originally Posted by Jason Beam
Member
So I guess there is no reason for lightning rods...
Member
Same reason you don't need airbags while walking ... it's a matter of scale.
Jason Beam
Sacramento, CA
beamerweb.com
Member
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.
Last edited by Art Mann; 07-22-2015 at 12:11 AM.
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.
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
"A hen is only an egg's way of making another egg".
– Samuel Butler
[OP]
Member
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?
NOW you tell me...
Member
But the blades all have guards over them.
Member
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.
Jason Beam
Sacramento, CA
beamerweb.com
Member
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"
Contributor
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
Bob C
Guest
This is why I've never understood the fascination with pvc.
Member
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.
Contributor
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.
Bob C
Member
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.
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