4" vs 6" duct for Dust collection?

Would a small shop DC system run ok with the mains at 4" smooth bore PVC ducting vs 6"? I would have about 30' of main and 4 drops using a 2hp 1600cfm unit and air blocks for the station no used. The DC has a 5" intake and 12" impeller.
I cannot find locally PVC 6" sewer and drain pipe. I can find galvanized 6" duct at about $1.40/ft and 4" smooth bore S&D PVC pipe at $0.58/ft. I hate to spend more of the duct then the DC which would happen if I go the metal pipe route.
I visited all local Home supply brands (HD, Lowes, CW) and all dont carry over 4" pVC. And I called an irrigation supply and they dont carry the light duty 6" PVC pipe (i think its schedule 2379 or something like that). Im guessing that its not a big seller inmy area for some reason to do with building codes for such things.
So any way, I was wondering how much performance I lose by going the 4" vs 6" route.
Any thoughts appreciated!
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In sheer volume of air moving, quite a bit of "performance loss". But with this much suction, I don't think you could improve the dust collection any better than "all of it", which you'll probably attain with this set-up. I think 4" is plenty for now, 'til you add on to the shop.(grin) Tom
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trs80 wrote:

For 30' of straight pipe, one wye, and 6' of flex hose, the 6" gives 2.25 inches of pressure, while the 4" gives 3.57 inches.
Whether the additional pressure is a problem will depend on the fan curve of your blower, hood losses, separator losses, filter losses, etc.
Chris
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I would go with 5" or 6". Do you have a plumber friend that can get plastic from a wholesaler? Also, where are you at? Your location may pop someone out of the wood work with a local supplier. Greg
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ok thanks. Im in Orange County, Ca.
thanks again

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You could check with Penn State Industries for metal ducting and they also have a design service. Also, remember that the more unusual the size or material the harder it is to get wye's, elbows and connectors. Even with using the 4" PVC I had to do a little fanigaling to make connections but at least it's doable. Your runs sound like mine and I'm having no problems with my cheap Harbor Freight DC and a 4" PVC main. I use gates right where the wye splits from the main for more efficiency (there's a name for that run from the wye to the gate to the machine and I decided to eliminate it). I also ran my main trunk at the level of the DC inlet so that the machine cuttings drop down to it further eliminating an element of resistance. Of course, anything I gained there I lost with the corrugated flex line from the machine to the gate at the wye. It's a bit of a balancing act and I let myself get tangled in all the technicalities for a couple of months before I just went ahead and 'made do' with the 4" main. I wasted a lot of time with all that fretting. Just do something. Oh, one more suggestion. Don't fasten everything with pvc cement or even caulk. Just drill and use sheetmetal screws until you're sure that you're satisfied and even then I'm sticking with this set up. It's easy to access in case of any issue such as a clog (got leaves stuck in the metal 'X' which protects the impellar.
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great advise....thanks.
What did you do for the blast gates? I assume something that senses what machine is on and then opens the gate?. Those look like they can get expensive. And to make something manual would not allow the gate to be near the main as it would be awkward to reach each time and odds are I would just leave it on.

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You should really remove the leaves from the tree before machining it.
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For more info than you ever wanted, visit Bill Pentz's website. He insists on 6" by the way. http://billpentz.com/woodworking/cyclone/Index.cfm
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I am currently using the setup your suggesting, only with a slightly tricked out Jet 1100cfm DC. Two zones 30ft or so 4" SD pipe w/4 drops on each zone. I don't know how much better 6" pipe would be but I do know it wasn't availiable locally so I used 4" and it is working fine for me. The first zone runs from separator up to ceiling across to right side of TS and back down and catches planer, TS, overhead guard and jointer. The second zone runs from the separator along one wall and catches the router table, band saw, one fitting for a future sander, and it finally reduces to 2 1/2" to facilitate shop vac hose/fittings for cleaning the shop. I put blast gates at all the machines plus a blast gate at the start of each zone so the DC isn't trying to suck air from the zone not being used. Someday I'm gonna pick up an anemometer just for kicks... Anyway, I'd suggest just using duct tape to join the fittings and pipe together. If you decide to change the configuration someday, it's easy to just cut the tape and pull it all apart. Also, avoid 90 deg elbows wherever possible, they will tend to clog. I switched to 45deg fittings to make smooth corners and haven't had a clog since. I found some reducers in the schedule 40 area that fit the 4"SD and reduced it to 3"pvc (IIRC) that the flex pipe fit over perfectly. I'll second looking over Bill Pentz website, information overload on DC's. --dave

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thanks. The Bill Penz site is what got me started. What are you doing for blast gates?

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I tried 14 different wholesalers for pipe in my area. Not one carries the 6" PVC S&D 2379 (thin wall inexpensive pipe). SOme said they could order it. Most had 6" SDR-35 which is about $2.50/ft.
So my options are down to using the metal ventilation 6" pipe ($1.40ft at Lowes) but I hear the adapters are very expensive....or.......
Keep all ducting at 4" PVC thin walled ($0.58 at Lowes).

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Just a thought here, and I'm not throwing stones.
After visiting that many locations, how much time & money did you spend in the travel?
Yes, there is a difference in what you use, and how efficient it is in getting the last iota of dust and debris from the output of your machines. But after a while, there is diminishing return from the quest. You're still going to hand sand, cut with a hand saw, chisel or hand plane. Dragging in stock, particularly rough or log style, brings in crud. At some point, there is going to be extra stuff on the floor, on your clothes, and in the air.
Your grandfather worked that way. So did my uncles. The last uncle died with a grin on his face at 94 years old last spring.
So decide. 4", or the 6" you can get. It's only money.
I put in the 4", if that means anything to you.
Patriarch
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uhhhh....it was phone calls.....not driving. Took 40 minutes. Its someting we enjoy here in California, modern communications. I hear it will be spreading to other parts of the country in the near future..

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I had to laugh! I live near SF, have been in the telecomm business for most of the last 25 years, and would likely still have gone and dug around the yard. Yeah, right.
Have fun with you new stuff!
Patriarch
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Huhhh?

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trs80 wrote:

We're waiting to see if it's just a fad.
--
Make yourself an honest man, and then you may be sure that there is one
rascal less in the world.
  Click to see the full signature.
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Well, 6" is better than 4", and 4" is better than 2". The larger pipe simply can move more air. There are other factors like length of pipe, turns, turbulence, etc. Four-inch DC pipe and connectors are easily obtained, plus many machines are fitted with 4" ports. You can compensate (a little) with a DC that moves more cfm.
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