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Thread: effect of curved vs straight inlet into DC?

  1. #1

    effect of curved vs straight inlet into DC?

    Hello, I took a look around but couldn't see this issue addressed anywhere so perhaps my friends here have an answer?
    in searching for an answer as to the benefits of a straight pipe vs a curved pipe into a cyclone (or any) dust collector. I've looked at hundreds of pictures of various shop setups. In many of the "this is my DC layout" articles, the writers mention how long sweep fittings, minimizing corrugated flex hose, subtle reducers etc are all good things. Then they show their actual DC unit with a set of 90's on the intake? My understanding is this is incorrect unless absolutely req'd to fit under physical requirements.

    I look at my 8" inlet on my 3HP Cyclone and although it would be nice to get the spiral pipe up near the ceiling asap to save headroom, by doing so if I follow the "rules " I'm adversely affecting my flow. It would seem that I should put a chunk of 8" on the inlet then at ?? feet utilize a few 45's to get the pipe up to the ceiling. ... or should I reduce it down to 7" right at the inlet (my main trunk will be 7" and drops 6").

    The idea of running say 5' (or something) of 8" pipe directly out of the DC then using 8" 45's to get to ceiling height (with some 8" pipe between them) and at that point, reducing down to 7" for the remained of the trunk is what I was thinking. But I see so many shop pics showing an immediate 90 degree pipe virtually right off the DC inlet. Am I presuming incorrectly that this is of significant negative flow reduction? Let's face it, I only (like all of you) want to do this once. It would certainly be less of a headache to immediately get the pipe up to the ceiling but again .... if it is going to cause a significant reduction in air flow speed? by doing so, I'll gladly suffer a few head bumps and run some straight line 8" directly out from the DC. (my max would be about 5')
    So my questions are;

    1) Is it of a significant advantage to have the inlet remain straight from the DC's inlet?
    2) Am I gaining much (if anything) by using 8" for 10' then reducing to my main trunk size of 7" once I hit my ceiling height?
    3) Or should I just reduce to 7" at trhe inlet and keep the main trunk line continuing at 7" or do I actually gain much from having some 8" initially coming out of the DC, going through a few 45's and then reduce once I hit my straight run 7" main trunk?

    Logic says one thing but as I mention, so many excellent woodworking shops I look at seem to have complicated gyrations of pipe coming immediately from the inlet pipe of the DC.

    Any pearls would be appreciated as always, Thanks !

  2. #2
    Join Date
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    The "best practice" is a straight run into the inlet when it can be physically supported followed by the largest sweep one can accommodate if it absolutely must be a curve because of "small shop dynamics". There is less turbulence with a straight shot in. There are certainly a lot of folks who otherwise have really nice duct work designs that fall down in performance because of "doing the hula" right in front of the collector. I'm a fan of running "native" inlet size for whatever reasonable length is practical in the shop. My cyclone has a 7" inlet and the duct work out to the first major branch stays at 7" with 6" thereafter because that was the then-current design thoughts. Shops with multiple tools running simultaneously generally get a duct design that steps so that maximum velocity/air flow is maintained. For most of us with one person shops, stepping is less important, but it may be practical/economical to do 6" with 6" and 5" drops to individual tools because of duct cost. For changes in direction...long sweep elbows actually made for dust collection are going to perform better than ganging up 45 elbows, but the expense of the them often gets in the way.
    --

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

  3. #3
    Thx Jim. I'm quite surprised at the amount of DC pictures I see where as you say, it looks like a bunch of spaghetti coming out of the (or should I say going into) the DC. My Grizzly 3HP has an 8" inlet but from reading so many reports it seems it might be a bit "ambitious" to run 8" for the main trunk. ( I think I saw Mr Pentz suggesting 6" with the 5hp Clearview) so that sort of scares me away from using 8" as a main trunk with 6" drops. I'll defer to your expertise as this is my first real foray into it. Since I'm going metal spiral, the difference between 7" & 8" isn't prohibitive to buy.

  4. #4
    Join Date
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    Scott,

    Somewhere at some point I read that having at least 5' of straight duct from the inlet is the minimum for maintaining the least turbulence.

    If your inlet is low enough that you need to go up with your ductwork why not raise the cyclone?

  5. #5
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    Sep 2016
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    Modesto, CA, USA
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    On my cyclone I put in a so called neutral vane and I had a meter on it so I saw how it helped the pressure. So I would belive a straight shot in would also help airflow/pressure. I belive the pressure varied by 1-2 inches of water with the neutral vane.
    Bill D

  6. #6
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    Any possibility of a picture of where the cyclone is going?

  7. #7
    Join Date
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    central tx
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    Here's what I did in the same situation. I have a 7" inlet. I had about 40" of straight pipe, then a 7x7x7 lateral wye, and used a 7x6x6 lateral wye at the ceiling. Oneida recommended a minimum of 24" of straight pipe before the inlet.


    IMG_2357.jpg

  8. #8
    Thank you for your insights. I've got an 8' ceiling. It was difficult to get my full 50 gal drum barrel under the unit and in accomplishing this, my cyclone motor now sits up between the ceiling 2x12 joists. I could have split the drum and lowered the unit utilizing the 35 gal drum but I do lots of jointing and planing. I'm all in for the idea of running a straight shot of pipe out of the inlet on the cyclone for say 5'. I mean it sounds very logical.
    So my only remaining Q is do you think I should use 8" fittings to get the main trunk line up to ceiling, or reduce to 7" fittings (45's) after the straight run of 5'? My thoughts were to use 8" fittings rather than "choking down" to 7" so as to minimize the air flow reduction from making this turn? ... I hate to come clean but my IT skill at transferring a pic to this thread is too high a hurdle for me.
    I can make the change in elevation (height of the intake to the main trunk line height) by using two 8" 45's (and not at their full 45 capacity) with a short chunk of 8" in between. Or is this whole idea of keeping to the 8" just a waste of $$ for virtually no real measurable gain vs 7"?
    Thank you again for everyone who has an opinion especially if you've been through this decision process. I'm alone, have no helpers, and really only want to be up on a ladder once. (even though I'm only up a few rungs!! I'm worried that at my age if I fall I won't bounce .. I'll just burst!

  9. #9
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    Quote Originally Posted by Scott Driemel View Post
    Thank you for your insights. I've got an 8' ceiling. It was difficult to get my full 50 gal drum barrel under the unit and in accomplishing this, my cyclone motor now sits up between the ceiling 2x12 joists. I could have split the drum and lowered the unit utilizing the 35 gal drum but I do lots of jointing and planing. I'm all in for the idea of running a straight shot of pipe out of the inlet on the cyclone for say 5'. I mean it sounds very logical.
    So my only remaining Q is do you think I should use 8" fittings to get the main trunk line up to ceiling, or reduce to 7" fittings (45's) after the straight run of 5'? My thoughts were to use 8" fittings rather than "choking down" to 7" so as to minimize the air flow reduction from making this turn? ... I hate to come clean but my IT skill at transferring a pic to this thread is too high a hurdle for me.
    I can make the change in elevation (height of the intake to the main trunk line height) by using two 8" 45's (and not at their full 45 capacity) with a short chunk of 8" in between. Or is this whole idea of keeping to the 8" just a waste of $$ for virtually no real measurable gain vs 7"?
    Thank you again for everyone who has an opinion especially if you've been through this decision process. I'm alone, have no helpers, and really only want to be up on a ladder once. (even though I'm only up a few rungs!! I'm worried that at my age if I fall I won't bounce .. I'll just burst!
    I would say for your main pipe I'd stay at 8" depending on your cost for the pipe. The main reason I necked down to 6" so soon was that I had a local supplier of 6" spiral and it saved me $800+. I mailed ordered two 5' lengths of 7" spiral plus a few fittings. Otherwise I would have kept that whole horizontal run at 7".

    At a minimum I would stay at 8" for the initial pipe and the two 45's. Not much cost difference there. When I was doing my static pressure calculations it does help to stay bigger longer especially for those initial turns.

  10. #10
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    I used an expensive computer program to illustrate what I would do. It will let you use a full size drum and eliminate one of the 45 elbows.
    Attached Images Attached Images

  11. #11
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    If your system is designed to support an 8" main...that's what I'd use. BTW, I have my Oneida's motor stuck up between the joists also so I could get the 55 gallon bin under it.
    --

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

  12. #12
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    I had this same concern when I was setting up the DC in my current shop. The ductwork design was done by Oneida and they put back-to-back 90s fairly close to the inlet to get the pipe up to the ceiling. I questioned that approach, but they said it would be fine. I haven’t had any problems with it, so I wouldn’t worry to much about it.

  13. #13
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    Quote Originally Posted by Scott Driemel View Post
    So my only remaining Q is do you think I should use 8" fittings to get the main trunk line up to ceiling, or reduce to 7" fittings (45's) after the straight run of 5'? My thoughts were to use 8" fittings rather than "choking down" to 7" so as to minimize the air flow reduction from making this turn?
    Don't know if it is right or not, but that is what I did; used 8" fittings to take the trunk up to the ceiling. It makes the turns much less sharp than the same in 7" would be. It is suboptimal, but I figure my 3hp cyclone is more powerful than I really need, so if I lose a bit, so what.

  14. #14
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    Thomas
    I have designed a lot of industrial ductwork in a major foundry. Yours is a system I would be proud to call my own.

    Peter
    Love the Sketch Down, I might tilt a cyclone 15 degrees and still hope it would work, but it probably would not. I have seen some water cyclones tilted at 45 degrees; was told that they work fine but am not yet convinced just how. They remove weld balls in auto paint shops.

  15. #15
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    The original owners of Clear-Vie tested one of their cyclones all the way over to horizontal. It separated dust just as it would normally except for chunks of wood that just spun around the upper section. So 45 would work. There are companies that make horizontal cyclones that have a chamber at the end with an outlet at the bottom instead of the cone. Cyclones don't rely on gravity for separation, it's the swirling and the reversal of the air that does it. I wish I had one of those little dust deputies for a vacuum cleaner to play with. I'd see how far it could be laid over and still work.

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