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Thread: duct size for vertical drops

  1. #1
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    duct size for vertical drops

    I have the Oneida V3000 and trying to finish my ductwork design. If I use the Pentz spreadsheet I think it is telling me I need to drop down to 6" pipe for the vertical drops at each machine even if its at the end of the run and I could stay at 7".

    My longest run ends up at 28' with 4 90's (2 - 90's and 4 - 45's to get up the vaulted ceiling) and 1 - 7" lateral wye.

  2. #2
    General rule is keep the ducts as big as you can as close as you can to machine.

  3. #3
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    Maybe I don't understand the spreadsheet.

    If I enter 800 CFM and 4000 for the target air velocity, I get about 6.17" of static pressure loss. I'll drop down to 1' of 5" flex hose for the hood

    The fan curve tells me I'll have about 1000 CFM

    The spreadsheet says the "Maximum Vertical Duct Dia without Plugging" = 6.21

    I had been planning on just running the 7" down the wall but this seems to be saying that I won't have the velocity to pull it up the pipe.

  4. #4
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    My general rule of thumb is vertical runs need to be slightly smaller than horizontal runs as you need more velocity for obvious reasons. 7" main, 6" vertical? perfect. Not just because that is what I did...
    NOW you tell me...

  5. #5
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    Personally, I'd do 6" or even 5" drops for the reason that Ole mentions...velocity.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
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    I think I'm going to do 7" only for about 5 feet out of the inlet and then 6" everywhere else. I have a local supplier for 6" spiral pipe and fittings and it saves me about $800 vs doing 7" for much further on the horizontal.

  7. #7
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    For a one person operation, that should work very well. My system is similar...7" from the inlet out to (in my case) the one place that the ductwork splits down to a 6" main run and a 6" heavy run over to my J/P. Zero complaints and it's been working very well for years.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
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    Quote Originally Posted by Jim Becker View Post
    For a one person operation, that should work very well. My system is similar...7" from the inlet out to (in my case) the one place that the ductwork splits down to a 6" main run and a 6" heavy run over to my J/P. Zero complaints and it's been working very well for years.
    Thanks for the feedback, good to hear from folks who have similar setups actually working.

  9. #9
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    Most of my actual "drops" are 5" with a few 4" where they are appropriate. The J/P is 6" to the gate but transitions to 5" to the machine since it has a 120mm port. Two of my floor sweeps are also 5" and they work extremely well.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
    My system is all 6 inch from the cyclone to the ceiling drops. Some of the drops are 6", one is 5", and some are 4". They all seem to work just fine, and I don't know that it would matter much if they were a different size. The only machine that really even remotely tests the capacity of the system is the 15" planer, and that is only when I am doing roughing passes on 12" white pine with its long sticky shavings. I've got a 5" hose on on that one going to the ceiling. It seems to be the right combination of velocity and clearance. I'd go larger, but the machine has a 4" port, and I think the speed might drop to much for 6" hose. Everything else is mostly fine or coarse sawdust or small chips, and they don't seem to be that picky about the size of pipe.

    I know there are ideal sizes of pipe and air speeds and the like, but in general, the size systems we put in small shops are often pretty forgiving from an engineering perspective and tend to work well enough unless something it way off. After you get a decent enough sized DC, the weak point is usually the port size and collection design of the tools.

  11. #11
    I think your plan will work well, and you'll see good results.

    I have 7" duct from my cyclone (2hp Oneida) to the first wye/drop and then 6" main after that.

    My drops are a mix of 6", 5" and 4"... The bandsaw at the end of the run is likely the most challenging, it gets a 6" drop split into two 4" ports. Seems to pull the dust up everywhere without issue...

    Good luck!

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