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  1. #16
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    Apr 2019
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    Fien/renovator/multi tool I found is the best thing to cut pvc pipe. Nice clean cut and pretty much a safe tool to use one handed as you roll the pipe following a line

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  3. #17
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    Feb 2006
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    Perth
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    Quote Originally Posted by havabeer69 View Post
    Fien/renovator/multi tool I found is the best thing to cut pec pipe. Nice clean cut and pretty much a safe tool to use one handed as you roll the pipe following a line
    These are indeed safe to use and are also really good for cutting rectangular slots and holes in plastic pipe. I also have a medical plaster cast cutting saw that does the same thing and use that to cut holes for screens/displays etc in plastic electronics instrument boxes. These types of tools are great if you already have them otherwise I’m not sure they’re worth purchasing just to install ducting. I will add this to the recommendations above.

  4. #18
    Join Date
    Feb 2006
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    Perth
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    Those of you that read the above recommendations may have noticed the "Static" section was missing. This has now been completed, along with an associated FAQ thanks to the assistance of member dmorse and I have added some picture to aid in the explanations. I hope you find this useful.

  5. #19
    Join Date
    Jul 2008
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    geelong
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    359

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    Have had the thought - NOT council friendly -or possibly neighbors either - of a basic cyclone on the end of the system and NO filtration. Should be more efficient - would obviously depend on the fineness of dust - sanding or thicknesser. Was the old school thing till regulated away (possibly for good reasons)

  6. #20
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    Feb 2006
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    Perth
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    Quote Originally Posted by wood spirit View Post
    Have had the thought - NOT council friendly -or possibly neighbors either - of a basic cyclone on the end of the system and NO filtration. Should be more efficient - would obviously depend on the fineness of dust - sanding or thicknesser. Was the old school thing till regulated away (possibly for good reasons)
    This has been discussed many times and as its OT won’t provide a detailed response. Maybe just to say that it depends very much on the cyclone and/or if you live on acreage. It’s not a problem for a cyclone like a Clearvue, others may not be as effective.

  7. #21
    Join Date
    Aug 2020
    Location
    Townsville
    Posts
    1

    Question

    Hi Bobl, wondering if you ever got a chance to test this semi rigid duct? If suitable I was considering using in a retractable dropper situation from an overhead trunk line. Overhead trunk being used to service multiple mobile workstations containing table saw, router, drum sander and also mobile thicknesser and bandsaw. So I was considering not servicing every station but have a few droppers and this duct would Ben better than using flex? I also have some static machines being drill press and lathe which the trunk will also service. Would like multiple drop downs to service multiple machines but because if necessity to move machines around shed want retractability to get them up out of the way when necessitated.

    Thinking this semi rigid may be part of a solution - join to trunk on wyes, blast gate at each Wye, and fabricate some form of easy on/off at machine end.

    I will be making mods to a 2hp dc using 150mm dimensions as you have described in the related thread with no cyclone but with both particle collector and venting on outside of shed with no filter to aid flow.

  8. #22
    Join Date
    Feb 2017
    Location
    Huntsville, AL USA
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    32

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    Storm water 90º bends have a very tight radius and are hence also restrictive but the standard DWV 90º bend has twice the radius of curvature and although is more expensive has a much lower flow resistance. This about the only DWV junction needed for 150mm and larger ducting. (my emphasis added)
    BobL, is the curvature of this single DWV plain 90-degree bend twice the radius of the pipe?

    All the 150mm (6") "sweep" PVC 90s that I can find here in the U.S. are only about 1.25R, not 2R, so I've been hesitant to use them.

    Related to this, if the curvature of this DWV plain 90-degree bend is less than 2R, would you still recommend using this over using a pair of 45-degree bends separated by a short bit of straight pipe?

  9. #23
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    Feb 2006
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    Perth
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    Quote Originally Posted by Rushton View Post
    BobL, is the curvature of this single DWV plain 90-degree bend twice the radius of the pipe?
    Sorry no picture appeared - this is probably because you are a first time poster and it will take about 5? posts before you are approved - email the pic to me @ [email protected]

    All the 150mm (6") "sweep" PVC 90s that I can find here in the U.S. are only about 1.25R, not 2R, so I've been hesitant to use them.
    Related to this, if the curvature of this DWV plain 90-degree bend is less than 2R, would you still recommend using this over using a pair of 45-degree bends separated by a short bit of straight pipe?
    The blue bars are tests on a 2R bend, right most bar is the average showing a~% loss
    Red bars are for a single 45º bend - average is also ~1%
    Green is for 2 x 45º bends average loss is a bit over 2%
    Purple is for 1R bends ie average is about 7%!

    Where the 1.25R bend would sit is somewhere in between the 2 x 45º and the 1R so I would go ahead and use the 2 x 45º.



    150mmbends2.jpg

  10. #24
    Join Date
    Nov 2016
    Location
    USA, Indiana, West Lafayette
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    188

    Default

    Quote Originally Posted by Rushton View Post
    BobL, is the curvature of this single DWV plain 90-degree bend twice the radius of the pipe?

    All the 150mm (6") "sweep" PVC 90s that I can find here in the U.S. are only about 1.25R, not 2R, so I've been hesitant to use them.

    Related to this, if the curvature of this DWV plain 90-degree bend is less than 2R, would you still recommend using this over using a pair of 45-degree bends separated by a short bit of straight pipe?
    First, in the US DWV is not normally used for dust collection. Sewer and Drain is what most people use. DWV has an OD that's compatible with pressure pipe, i.e., Schedule 40 or 80. S&D is ASTM-2729 or ASTM-3034 (e.g., SDR35). Different OD and different fittings.

    Second, US curvature names are not the same as Bob's. Bob gives the ratio of curvature radius to pipe inside radius. In the US it's referenced to inside diameter. So, Bob's 1R is .5R in the US.

    A common S&D sweep 90 is .833R US or 1.67 Bob. It will have less loss than two .5R/D 45s.
    Ninety_75rD_2.jpg
    Dave

  11. #25
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    Feb 2006
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    Perth
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    Quote Originally Posted by dmorse View Post
    First, in the US DWV is not normally used for dust collection. Sewer and Drain is what most people use. DWV has an OD that's compatible with pressure pipe, i.e., Schedule 40 or 80. S&D is ASTM-2729 or ASTM-3034 (e.g., SDR35). Different OD and different fittings.
    Here in Oz we have two types of pipe commonly used for dust extraction, DWV, used for sewer pipe (grey coloured) and comes in different wall thicknesses (pressure ratings)
    The other pipe is Storm Water (SW) which is cream/white coloured and is not defined by wall thickness (it's thinner than DWV) but stiffness.

    For 4"/100mm or less, DWV and SW are not dimensionally compatible but above this size they are. DWV fittings are thicker, have longer overlaps on pipe fittings, and bends have longer radii of curvature. There is no 100mm SW available, the nearest is 90mm which is rubbish for dust collection.

    Many stores will not stock the full range of fittings for 6" or larger - they many only stock DWV fittings since these cover both applications

  12. #26
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    Feb 2017
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    Huntsville, AL USA
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    Bob, thanks for your reply. The image to which I was referring is in your post #4 of this thread. Your charts are most helpful, thank you.

  13. #27
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    Feb 2017
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    Huntsville, AL USA
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    dmorse, thanks for clarification on the terminology. I'm working with D-2729 and SDR35 pipe for our dust collection system. I was not aware that the terms "S&D" vs "DWV" held a meaningful distinction.

    So, to be clear: in the U.S., you believe that the sweep 90 in your drawing will have less loss than paired 45s? If so, this is not jiving with what I think I'm seeing for 6" in the Cincinnati Fan Engineering Data pdf (page 9) which I've been trying to understand. Not being argumentative at all - just trying to understand what to use!

  14. #28
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    Nov 2016
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    USA, Indiana, West Lafayette
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    The table on that page does not go below 1.5 R/D. How are you extrapolating that to .5 and .833?

    ASHRAE/SMACNA tabulate the following
    Code:
    R/D    Loss coefficient
    0.5     0.71
    .75     .33
    1.0     .22
    So .833 R/D will have a loss coefficient between .22 and .33, much less than the .71 of a sharp turn. Note that the 45s are .5 R/D.

    You can only compare loss coefficients qualitatively to Bob's data. His numbers apply only to his setup. The ordering remains the same but relative values can be different. Loss coefficient is the ratio of pressure loss to velocity pressure, not the ratio of two flow rates.
    Dave

  15. #29
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    Feb 2017
    Location
    Huntsville, AL USA
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    Default

    Hi Dave, thanks for your continued efforts to educate me on this. I hope the conversation can help others also trying to figure out best practices for our dust collection ducting.

    I'm looking at the Cincinnati Fan data very much as a lay person with no background in the engineering, and certainly none in fluid dynamics. I've spent a lot of time reading Bill Pentz's materials and I understand the desirability of using long sweep 90s (2R or greater) versus shorter radius 90s. I'm trying to get some firmer test data or engineering data that supports whether to use some given sweep radius 90 versus pairs of 45s. My focus is on 6" pipe.

    When I look at the Cincinnati chart (shown below for convenience), I note that with 6" pipe has a coefficient of 12 at 1.5R and 7 at 2R. A 45 degree elbow is stated to be one-half each of these. So, I'm thinking if I use a pair of 45s spaced by some straight pipe, that combination will still have a loss coefficient less than a .833 R.D 90 even if not as good as a 1.5R 90.

    Cincinnati Fan Resistance Loss Chart for Elbows.jpg
    (open in new tab to see full size)

    So what am I not understanding here in making my leaping guess? Is it that I'm not taking into account the R/D of the 45-degree elbow I may be using and that a tighter radius 45 will be more similar to the loss resistance of the .833 no matter how I space them apart? In other words, to make my leap I'd need to be sure I'm using 45-degree elbows manufactured to that same 1.5R or 2R radius?

    I suspect that, just as there are no 1.5R or 2R radius D-2729/SDR35 90-degree elbows, there are no 1.5R or 2R radius 45-degree D2729/SDR35 elbows. Correct?

  16. #30
    Join Date
    Nov 2016
    Location
    USA, Indiana, West Lafayette
    Posts
    188

    Default

    Quote Originally Posted by Rushton View Post
    Hi Dave, thanks for your continued efforts to educate me on this. I hope the conversation can help others also trying to figure out best practices for our dust collection ducting.

    I'm looking at the Cincinnati Fan data very much as a lay person with no background in the engineering, and certainly none in fluid dynamics. I've spent a lot of time reading Bill Pentz's materials and I understand the desirability of using long sweep 90s (2R or greater) versus shorter radius 90s. I'm trying to get some firmer test data or engineering data that supports whether to use some given sweep radius 90 versus pairs of 45s. My focus is on 6" pipe.

    When I look at the Cincinnati chart (shown below for convenience), I note that with 6" pipe has a coefficient of 12 at 1.5R and 7 at 2R. A 45 degree elbow is stated to be one-half each of these. So, I'm thinking if I use a pair of 45s spaced by some straight pipe, that combination will still have a loss coefficient less than a .833 R.D 90 even if not as good as a 1.5R 90.

    Cincinnati Fan Resistance Loss Chart for Elbows.jpg
    (open in new tab to see full size)

    So what am I not understanding here in making my leaping guess? Is it that I'm not taking into account the R/D of the 45-degree elbow I may be using and that a tighter radius 45 will be more similar to the loss resistance of the .833 no matter how I space them apart? In other words, to make my leap I'd need to be sure I'm using 45-degree elbows manufactured to that same 1.5R or 2R radius?

    I suspect that, just as there are no 1.5R or 2R radius D-2729/SDR35 90-degree elbows, there are no 1.5R or 2R radius 45-degree D2729/SDR35 elbows. Correct?
    The issue is that the only 45s available are .5R/D. According to the Cincinnati Fan chart you showed, two of them should have the same loss as a single 90, although Bob's data shows it to be less. The SMACNA/ASHRAE shows a .5 R/D 90 to have a loss coefficient of .71 (that is, per Cinc., each 45 is .71/2 and two of them are twice that), while a .833 interpolates to .28. That's a big difference.
    Bend Loss.png
    Dave

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