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Thread: Dust collector air flow measurements

  1. #1
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    Dust collector air flow measurements

    Iím changing up my dust collection and figured Iíd check my flows while Iím at it to see if my changes make measurable differences. I went to buy one of the vane anemometers on Amazon and the geek in me convinced me to look for something that may be semi-accurate.
    I see measurements with these posted a lot but I also know itís very inaccurate.
    I know thereís not much that can be trusted on Amazon with instrumentation. But some things are both cheap and reasonably accurate.
    The pitot tube devices seem like they should work and one could map a duct to get a decent average (given a straight run long enough for fully developed flow). Iíve never tried any of the Amazon digital manometers. One could check it with a homemade water nanometer. Has anyone used these?
    I see you can get some hot wire anemometers. Those seem like theyíd have some chance of being reasonable. But would likely need checking against the above mentioned pitot setup or such.
    Iím hoping to get some decent advice to learn if it is worth getting something cheap from Amazon for my shop use without going through the cost and effort of trial and error.
    In the end the vane anemometer probably would give a reasonable comparison of the effect of the changes. But Iíd like to have a somewhat trustworthy flow measurement just because of that geek side of me.

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    See my post from a while back here; https://sawmillcreek.org/showthread....fer&highlight=

    LMK if you're intrrested.

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    Dwyer makes well respected equipment but I use this lower cost pitot-static tube.

    I have a manometer that's an older version of this one and it's ok but I prefer this one, in part for it's Bluetooth data logging ability.

    I also have a hot wire anemometer but it has some difficulties in dust collection size ducts. It's good at HVAC velocities though.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

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    Thanks David! Those were exactly what I was looking at on Amazon. Iím hoping the cheap digital manometer gives accurate enough readings. Itís easy enough to check with a homemade inclines u-tube manometer it seems. Hopefully, the pitot tube is made well enough for some light use. Iíve put those on order.

    John it looks like you have some equipment youíll loan. Iíll get the pitot tube measurements and see how that goes. If I find Iím unable to get reasonable measurements with the pitot I may take you up on the offer. I can certainly report back some of my readings along with improvements.

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    The Australian Woodworking forum has a lot of information and well researched data on measuring air flow and it is the only place I know of that has good data that can be trusted done by someone who actually knows what he is doing.
    Chris

    Everything I like is either illegal, immoral or fattening

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    Thanks Chris! I looked briefly and it does look like there are several threads out there addressing my hunt for a low cost and fairly accurate method for measuring flows and pressures. Pitots and manometers seem popular. I did see a link to a Wood magazine article. I wasnít crazy about all their methods but it appeared better than most (https://www.woodmagazine.com/video/dust-collector-test).

    I understand the science and have practical experience in the measurements and analysis. This is why seeing those prop anemometers used makes me cringe!

    Itís been a while now (around 20 years ago now) but I spent about 5+ years doing measurement and analysis for nuclear plants to determine their capability of removing heat load during accident scenarios. It involved many measurements of their systems including air flows for heat exchangers and such. I had to also determine all measurement uncertainties and project those to accident conditions. The plants must have enough capacity including the extrapolated uncertainties to remove accident scenario heat loads to prevent meltdown. Iíve even authored a text and taught a class for the nuclear industry sponsored by EPRI on the measurement and analysis so the plants could maintain a program to measure and verify they met the NRC requirements.

    While I have knowledge and experience in that area, I havenít measured a small system such as my dust collector. So these forums and info are very helpful. Heck This weekend is the first time I did the math and I was quite surprised with the results. You know what assuming does!

    Obviously, when I did such measurements professionally we had some of the best instrumentation and all very well calibrated and maintained. I have been pleasantly surprised with some cheap instrumentation from Amazon and such sources. But I also know most arenít remotely what the claims say.

    I will add those vane/prop anemometers stuck on an open duct with who knows what flow sections prior to it are useful in proving oneís theory. I mean you could pretty much get that to read anything you wanted it to ;-)

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    Quote Originally Posted by Eric Arnsdorff View Post
    Thanks Chris! I looked briefly and it does look like there are several threads out there addressing my hunt for a low cost and fairly accurate method for measuring flows and pressures. Pitots and manometers seem popular. I did see a link to a Wood magazine article. I wasnít crazy about all their methods but it appeared better than most (https://www.woodmagazine.com/video/dust-collector-test).

    I understand the science and have practical experience in the measurements and analysis. This is why seeing those prop anemometers used makes me cringe!

    Itís been a while now (around 20 years ago now) but I spent about 5+ years doing measurement and analysis for nuclear plants to determine their capability of removing heat load during accident scenarios. It involved many measurements of their systems including air flows for heat exchangers and such. I had to also determine all measurement uncertainties and project those to accident conditions. The plants must have enough capacity including the extrapolated uncertainties to remove accident scenario heat loads to prevent meltdown. Iíve even authored a text and taught a class for the nuclear industry sponsored by EPRI on the measurement and analysis so the plants could maintain a program to measure and verify they met the NRC requirements.

    While I have knowledge and experience in that area, I havenít measured a small system such as my dust collector. So these forums and info are very helpful. Heck This weekend is the first time I did the math and I was quite surprised with the results. You know what assuming does!

    Obviously, when I did such measurements professionally we had some of the best instrumentation and all very well calibrated and maintained. I have been pleasantly surprised with some cheap instrumentation from Amazon and such sources. But I also know most arenít remotely what the claims say.

    I will add those vane/prop anemometers stuck on an open duct with who knows what flow sections prior to it are useful in proving oneís theory. I mean you could pretty much get that to read anything you wanted it to ;-)
    Thanks for the feedback and your experience in related fields. BobL who does all the research on that forum is a physics professor who designed and built world leading clean rooms so he understands what was missing and took steps to educate us about air flow and duct design. It is without doubt the best source of information for woodworkers and most of the answers are there. The sticky threads have a lot of information and are of course readily found rather than having to wade through the whole forum.
    Chris

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    I've got a buddy who does HVAC. He let me borrow this, which did well enough for measurements on the ability's of a hobby woodworking shop. I was able to double check the readings with a hot wire Anemometer, generously let from a fellow creeker, which gave similar results. My understanding is that the hot wire versions aren't necessarily more accurate, but they do appear to be about twice the price. The big advantage would be measuring in duct by drilling a small hole, but for our purposes, it's all about measuring the results at the tool, not in the duct.

    I think it's important to realize that we're trying to get nice round number results to see if we're hitting the mystical 1000 fps necessary to get the fine dust, and also to see if tweaks effect the overall system. A few feet (or a few hundred) feet off doesn't matter a massive amount in these circumstances.

  9. #9
    Quote Originally Posted by David L Morse View Post
    Dwyer makes well respected equipment but I use this lower cost pitot-static tube.

    I have a manometer that's an older version of this one and it's ok but I prefer this one, in part for it's Bluetooth data logging ability.

    I also have a hot wire anemometer but it has some difficulties in dust collection size ducts. It's good at HVAC velocities though.
    I have the Testo 405i hot wire anemometer. It is limited to 30 m/s which is 5905 fpm. Both of my dust collectors exceed this in 4 inch duct. I find it useful for checking air velocity in gaps around the tool cabinet. I also have the Testo 510i manometer. It could measure flow with a Pitot tube. But I only have a static pressure probe for measuring differential pressure to ambient mainly for measuring filter clogging. I think the vane type anemometer also works well for this kind of testing.
    Last edited by Thomas Wilson; 05-08-2022 at 10:34 PM. Reason: Error in units. FPS should have been FPM.

  10. #10
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    Quote Originally Posted by Andrew More View Post
    I've got a buddy who does HVAC. He let me borrow this, which did well enough for measurements on the ability's of a hobby woodworking shop. I was able to double check the readings with a hot wire Anemometer, generously let from a fellow creeker, which gave similar results. My understanding is that the hot wire versions aren't necessarily more accurate, but they do appear to be about twice the price. The big advantage would be measuring in duct by drilling a small hole, but for our purposes, it's all about measuring the results at the tool, not in the duct.

    I think it's important to realize that we're trying to get nice round number results to see if we're hitting the mystical 1000 fps necessary to get the fine dust, and also to see if tweaks effect the overall system. A few feet (or a few hundred) feet off doesn't matter a massive amount in these circumstances.
    1000 FPS is easy to get, use 6" duct and ports on the machine and a 15" impeller at 60hz/3450RPM and the job is done. No magic is involved, it simply works.
    Chris

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    Andrew where did you see 1000 fps for fine dust?
    This seems a bit unreasonable (60,000 fpm). This sounds like jet speed measurement range.

  12. #12
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    1000 fps is the delta that Bill Pentz arrived at and it has become the default number that is aimed. Actually my statement on 6" is what we use in Oz because 7" is not available here in any shape or form but some people in the US reckon 7" is better but I have never seen any data proving it. The ducting for a 16" impeller is of course much bigger, the recipe I use for that is 225mm main duct with 6"/150mm drops to the machine. I have been speccing installations using these numbers for many years as I was the agent for Clearvue here and those numbers work.
    Chris

    Everything I like is either illegal, immoral or fattening

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    Hey guys - check your numbers.
    60000 fpm (1000 fps) is around 12,000 CFM in a 6Ē round duct.
    Granted I have worked with equipment that couldíve done this - but it would not have fit in most of our shops!

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    Quote Originally Posted by Eric Arnsdorff View Post
    Hey guys - check your numbers.
    60000 fpm (1000 fps) is around 12,000 CFM in a 6” round duct.
    Granted I have worked with equipment that could’ve done this - but it would not have fit in most of our shops!
    FPS is a mistake, it should be CFM.
    Chris

    Everything I like is either illegal, immoral or fattening

  15. #15
    Quote Originally Posted by Eric Arnsdorff View Post
    Hey guys - check your numbers.
    60000 fpm (1000 fps) is around 12,000 CFM in a 6” round duct.
    Granted I have worked with equipment that could’ve done this - but it would not have fit in most of our shops!
    I corrected my post. 30 m/s is 5905.51181102 fpm not 5950 fps.

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