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Thread: Is it really necessary to tape the pvc joints of your DC plumbing?

  1. #46
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    Look at the 3 piece 90, 1C on the chart which is essentially what you make with a couple 45s. It has a resistance of 61', 48', 39'. So the best you'll get if there is some space between them will be 39' but perhaps more because there are the 4 ridges where each pipe to elbow joint is.

    I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate.

  2. #47
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    Grizzly recommended I leave another gate open on a different branch than the tool i was using on my 3hp cyclone. The increased air flow would let the rotor spin up to full speed and actually increase the air flow from my tool.

    I tried it with an anemometer and found it didn't make much difference either way. So now I try to close other gates, but don't spend much time on it.

    If having a gate open doesn't hurt anything, a little leakage from joints can't be so bad.

  3. #48
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    Quote Originally Posted by Wade Lippman View Post
    Grizzly recommended I leave another gate open on a different branch than the tool i was using on my 3hp cyclone. The increased air flow would let the rotor spin up to full speed and actually increase the air flow from my tool.

    I tried it with an anemometer and found it didn't make much difference either way. So now I try to close other gates, but don't spend much time on it.

    If having a gate open doesn't hurt anything, a little leakage from joints can't be so bad.
    That doesn't make sense and is just bad advice. The impeller/motor will spin faster when there is little airflow, as it is spinning in a higher vacuum and there is less air resistance. Look at any fan curve and more static head (vacuum, suction) means less airflow. Put your hand over a shop vac hose and you will hear the motor speed up as it has no air to move. The motor does the most work, and will therefore spin slightly slower when it is under maximum load, and that is when it is moving the most air with the gates open.
    NOW you tell me...

  4. #49
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    Quote Originally Posted by Peter Christensen View Post
    I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate.
    There are obvious choices other than PVC and spiral steel (Nordfab) that can give you economy and steel ducting at the same time. I am not even going to mention what it is for fear of sounding like a broken record.
    NOW you tell me...

  5. Quote Originally Posted by Peter Christensen View Post
    I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate.
    And just a reminder that DWV and Sch 40 aren't interchangeable (different ODs) so once the choice is made, there's no mix and match.

  6. #51
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    Quote Originally Posted by Ole Anderson View Post
    ............ I am not even going to mention what it is for fear of sounding like a broken record.
    I'm new here so haven't heard the playlist. If you don't want to say then how about a link to the tunes?
    Thanks

  7. #52
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    Quote Originally Posted by Peter Christensen View Post
    BobL on the woodwork forum in Australia discussed a PDF engineering book from a US company with a lot of data on duct, elbow, wyes, etc. It showed that 2 45s did have more drag than a tight 90 elbow. A 1.5 x diameter radius 90 was best. Using the cell or I would link the PDF.


    PDF is Loren Cook Engineering Cookbook. Page 54.
    BobL has done his own testing and it showed that a single 90 performs better than two 45"s which when you think about it sort of makes sense. The first 45 degrades the flow then the second 45 does the same to the already reduced flow whereas a single 90 only affects the flow once without the compounding loss. The figures are all there and illustrated for those who are curious about these things.
    Chris

    Everything I like is either illegal, immoral or fattening

  8. #53
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    Quote Originally Posted by Peter Christensen View Post
    I'm new here so haven't heard the playlist. If you don't want to say then how about a link to the tunes?
    Thanks
    Many of us have used 26 gauge snaplock steel HVAC duct very successfully. Slightly more than PVC, but way less than spiral pipe. But stay away from the much thinner 30 gauge stuff you may find at the BORG, it can collapse with a strong suction. You will generally find it cheaper at an HVAC supply house or local sheet metal shop than online. No issues with static. And it looks professional.
    Attached Images Attached Images
    NOW you tell me...

  9. #54
    Just to be clear about the 2-45s vs 1-90 (apples to watermelons comparison). The idea of using 2 45s instead of one 90 will always increase flow if it increases the radius. That is how the suggestion first started. Most snap lock and pvc fittings have inexpensive 90s, but come with a small <1 radius. If in those situations when you use 2-45s and make a longer radius 90 you will increase flow (as shown in this video https://www.youtube.com/watch?v=oXd6YlCnyzQ). If available a smooth long sweep 90 will always be better, which was the goal of 2-45s. Unfortunately long radius pvc or snap lock 90s are not readily available and usually significantly more expensive. Somewhere along the way the point of increasing radius in the curve has been lost and it has become a 2-45 vs 1-90 (apples to watermelons) comparison.

    Ole is correct about the possibility of long straight 30 gauge snap lock (from big box stores) collapsing under pressure. However a simple wooden ring around the mid-span of long straight ducts will eliminate the issue and add a mounting point for you.

    Hope that helps.

    Carl

  10. #55
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    Quote Originally Posted by Chris Parks View Post
    BobL has done his own testing and it showed that a single 90 performs better than two 45"s which when you think about it sort of makes sense. The first 45 degrades the flow then the second 45 does the same to the already reduced flow whereas a single 90 only affects the flow once without the compounding loss. The figures are all there and illustrated for those who are curious about these things.
    Carl just said it above me but one must CLARIFY what the radii are when comparing the "2 45s" vs. "1 90" flow question. I'm not sure if 45s come with different radii but certainly 90s do. When I was picking up my SDR35 (DWV, S&D, not Sch40) fittings from McMaster-Carr a decade+ ago, two 45s were significantly (IMO) cheaper than the long-radiused 90 so I went that route. And as it turns out, for my situation, having 2 45s in place of 90 was handy for directing my pipe.
    Wood: a fickle medium....

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  11. #56
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    Quote Originally Posted by Chris Padilla View Post
    ... And as it turns out, for my situation, having 2 45s in place of 90 was handy for directing my pipe.
    Same here. In fact, in snaking my 6" pvc through the trusses above the ceiling I had several places where four 22.5-deg elbows made the installation easier. By rotating some a few degrees the pvc almost turns into flex! Who knows what efficiency, but with the 5hp clearvue I have a clear excess of capacity at the machines according to the particulate counter.

    JKJ

  12. #57
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    Quote Originally Posted by John K Jordan View Post
    Who knows what efficiency, but with the 5hp clearvue I have a clear excess of capacity at the machines according to the particulate counter.

    JKJ
    That small point escapes a lot of people. It also depends on the configuration of the Clearvue and the speed it is running at. Never the less it is good to know these things and keep up to date with what others are finding.
    Chris

    Everything I like is either illegal, immoral or fattening

  13. #58
    This ain't much, but I've been shopping online for ways to build my duct system and it occured to me that, if in fact the cavities created by pvc joints does reduce flow, by simply belt sanding an angle on the end of the pipe equal to the angle inside the fitting, applying silicone, sliding it in and wiping the eccess silicone off, the smoother joint should result in improved flow.

    Like I said....not much, but if you cannot afford to overcome inefficiencies with hp, why not?

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