(09-29-2022, 02:18 PM)Cabinet Monkey Wrote: Certainly you're aware that the LT curve was derived using 8" duct, yes ?
And, that 6" duct has nearly twice the static pressure per foot of length of 8" ? And 4" duct twice the s.p. of that ?
And, that the volume that DC can move doesn't really change between 8" or 6" or 4" pipe ?
The velocity of the air moving in those pipes will change depending on size , but the collector's max flow is fixed by its fan, motor, and inlet.
8" ducting needs just over 1200 cfm to maintain a velocity of 3500fpm and you can see from Laguna's chart - that will get you in to the 7-8 inches of water column for static pressure. Which is hefty.
You seem to be fixated on the notion that a duct network needs to have the same size pipe from collector to tool. It does not. It can work, but so can a 10 to 20ft section of flex hose. Should we just recommend juss1 get a piece of flex hose because that'd be the fastest , cheapest way to to get the max rated cfm from his machine ?
Maybe you should read up on dust collector duct design before we go any further, because if you think CFM is constant regardless of duct size we aren't going to make any progress. Here's one article that should help. Link
When l installed mine.....l just "did" it. Sweating the details, crunching numbers, etc. is gonna put you in a rubber room.
Had what I thought was a good plan and went with it. It worked, got lucky?, maybe. You have to start somewhere.
3hp Dust Gorrilla, 8" y at the cone, 4' of 8", 4' of 7" each direction, all spiral. Then 6" sewer & drain pvc to 4" blast gates & 4" flex to each machine.
One thing, no 90° elbows, all 90° turns are 2 - 45's with a short straight in between.
8" pvc discharge outside, 55 gallon drum for chips.
(09-29-2022, 09:12 PM)EdL Wrote: When l installed mine.....l just "did" it. Sweating the details, crunching numbers, etc. is gonna put you in a rubber room.
Had what I thought was a good plan and went with it. It worked, got lucky?, maybe. You have to start somewhere.
3hp Dust Gorrilla, 8" y at the cone, 4' of 8", 4' of 7" each direction, all spiral. Then 6" sewer & drain pvc to 4" blast gates & 4" flex to each machine.
One thing, no 90° elbows, all 90° turns are 2 - 45's with a short straight in between.
8" pvc discharge outside, 55 gallon drum for chips.
Over 100' of pipe and yea, it sucks.
Ed
Your description shows you have a pretty good understanding of how DC systems work, so I don't think you just got lucky. On the other hand, the calculations to assess the expected CFM and static pressure loss in any particular design under consideration aren't going to put you in a rubber room, so it's better to run them rather than build something that doesn't work.
So I ended up buying 6" spiral ducting. The calculations I got seemed to indicate the longest run I had would yield similar cfms. I guess I'll know for sure after I put it together and slap an anemometer to it.
My question now is what hardware to use to install it. The place I bought it from weren't much help. At least the guys at the desk. Every question was answered with "it depends". I did end up buying the duct tape they normally use and some sealant (caulking type material). My initial thought was to use just that. On my old setup using 4" SD I just used flexible tape but I think there was a decent amount of leaks. Another option would be to use sheet screws but I thought that would unnecessarily restrict air flow and catch larger chips. Thoughts?
One of the basic concepts in fluid dynamics that escapes many when looking at DC piping as well as water pipe, is that of the area of the cross section of different size pipe.
EG 8” pipe has an area of 50.265 square inches
7” pipe has an area of 38.484 square inches
6” pipe has an area of 28.274 square inches
4” pipe has an area of 12.566 square inches
Of course turbulence introduced by a variety of factors from tubing type, angle of turns, number if turns, even direction of slip joints also effects final performance.
I can certainly understand why a manufacturer would tell its employees not to engage in the practice of recommending ducting, as there is plenty of room for misunderstanding, in addition to it being an immensely complex topic.
The debates I have noticed on here over the years, generally leave out so much detail as to be virtually useless.
I do occasionally notice a nugget of useful information though, and there are a couple in this thread.
One was the answer to any question always begins with “it depends”. No good plan survives first contact, so even though you may have purchased an ideal pipe layout, all it takes is one mis step during installation such as denting a main duct to increase turbulence and you no longer have the best airflow.
Size of main duct also depends on several factors, ALL of which impact function.
Size of DC, filter type, length of run, corners, type of transition to smaller duct, angle of transition, and the list goes on almost endlessly.
I am a tinkerer almost more so than a woodworker, and I still use multiple DC’s that roll from machine to machine because it works for me, and I know that I’d probably spend a fortune configuring, and reconfiguring ductwork on an almost endless loop.
So you can either chase ever decreasing steps toward improving performance while cost goes up, or make your best guess as it seems you have done and then ignore these threads in the future.
Just my 2 cents worth, and as my father used to say “for that and a dollar you can get a cup of coffee”
I wouldn't use duct tape, instead get some of the foil tape. Duct will come loose over time, the foil stays stuck. Also, though I don't see a problem with screws, on the straight runs the foil tape will have sufficient strength to hold things together. For drops and such bring in the screws.
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.
(09-14-2022, 11:26 AM)Cabinet Monkey Wrote: fred - you'd almost certainly be wrong
If you'd look a bit more closely at LT's marketing fluff you'd see they also state the real world , or connected airflow is 1600 cfm +/-.
So, what's more likely: the guy in marketing coming up with the 2700cfm # or the fluid dynamic engineer that designed the cyclone with an 8" port ?
If you'd care to look at Cliff's V-3000 spex , you'll notice it has a 7" inlet - which is what their duct designers suggested he go with. Pretty safe to assume they know he has tools with 4" (or smaller) dust ports. If 6" were as good or better, don't you think they'd have mentioned that being that 6" pipe and fittings are much easier to source ?
This is not how good dust collection pipe networks are designed. The main line is bigger than the branch lines, sub branches taper again if necessary.
Adequate or acceptable would probably be a better word choice. Especially not knowing all the other variables in the equation.
Bottom line is that saying just use "x" inch duct and you'll be good is short sited.
The conspiracy nut in me says Oneida might spec 5" and 7" because they're readily available -- from Oneida. From other sources? Perhaps not so easy. Admittedly this is not something I've researched, I have PVC. And it hasn't blown up or caught fire once.
I used 1/2" screws at every joint. If I was using duct that had special connectors, I'd use those. I taped every joint with AC duct tape, and I caulked every seam in the elbows. I saw a marked improvement in SP after I did all the caulking and taping.
So much pontification, which means nothing without data to support it. For those who think 8" ducting is the best choice did you stop to look at what will happen if you open only a single 4" blast gate? The fan curve data block shows that fan will pull 938 cfm (best case, because it's on that short test pipe and with new filters). Through an 8" duct 938 cfm = 2687 fpm, well short of the 3500 fpm you need in a trunk line to keep chips suspended. Of course, if you open two blast gates you will get more flow, enough to stay above 3500 fpm, at the expense of added power. If you went with 6" ducting on that fan the velocity with one 4" blast gate open would be 4777 fpm, which gives you lots of cushion for when the filter gets plugged up.
Either duct can be made to work. For a cabinet shop you would likely opt for the 8". But you'd likely also opt for a larger DC unit, too. For the OP, 6" ducting will easily meet all his needs. It costs less and will be easier to install, and the higher duct velocity will tolerate higher filter loading before stuff starts dropping out.
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