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Thread: Checking CFM Of A Dust Collector

  1. #1
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    Checking CFM Of A Dust Collector

    I'm looking for recommendations for a low cost held anemometer to help me figure out my CFM flow rate on a dust collector system I'm working on.

    I don't need anything fancy, But I also don't want anything that won't hold up to the higher flow rates of a dust collector.

    Doug

  2. #2
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    Quote Originally Posted by Doug Walls View Post
    I'm looking for recommendations for a low cost held anemometer to help me figure out my CFM flow rate on a dust collector system I'm working on.

    I don't need anything fancy, But I also don't want anything that won't hold up to the higher flow rates of a dust collector.

    Doug
    Did you check out Bill Pentz's info? He describles how to test and evaluate a DC including how to calculate CFM.
    http://www.billpentz.com/Woodworking...easurement.cfm

    JKJ

  3. #3
    https://www.testo-direct.ca/product/...ire-anemometer

    The above is supposed to be good and doesn’t give the erroneously high readings you get with a propeller type. I believe it takes care of the calculations.

  4. #4
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    Quote Originally Posted by John K Jordan View Post
    Did you check out Bill Pentz's info?
    Yes I did, But a lot of his set-up equipment looks to be complicated & costly!

    He does state that most anemometers are scaled to a lower FPM, Like usually fond in HVAC systems!

    "Most anemometers are scaled to read up to a maximum of around 6000 FPM, but it is better to have one that can measure up to 10000 FPM for working with dust collection systems."

    Doug

  5. #5
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    Quote Originally Posted by Peter Christensen View Post
    The above is supposed to be good and doesn’t give the erroneously high readings you get with a propeller type.
    Thanks for the link!
    That would probably work for over 98% of people, But I'm one of the few that don't use a "Smartphone"

    As for the "erroneously high readings you can get with a propeller type", I believe that has a lot to do with how the meter is being held?

    I've seen several videos where they have mounted the meter to a block or fixture to help keep it steady and at a set distance from the duct.

    One that's on my list is a HoldPeak HP-856A
    http://www.holdpeak.com/Product/pdetail/id/313.html
    With a max reading of 8800 ft/min, It's one of the few that reads over 6000 ft/min!
    It also has a threaded fitting on both the handheld fan unit & the main unit so it would be easy to mount to a fixture. It can also be connected to a PC with a USB cable so you store the data.

    Doug

  6. #6
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    I have this and it works very well. No way to check if it gives accurate readings, but I know it's in the ballpark.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

  7. #7
    "As for the "erroneously high readings you can get with a propeller type", I believe that has a lot to do with how the meter is being held?"

    Doug one of the reasons they give bad reasons is
    because of the area of the fan. The air has to speed up to get around and through it. That is where the errors come from. They work for a big opening but not the small ones of the pipes we use. There are all in one hot wire units from China for about $65 to $125 or so that can read to 6000fpm but I haven't found anything higher. Poke around Aliexpress and Alibaba. The unit I linked will work with an iPad or maybe some tablets. They also have a manometer unit that can check airspeed with a pitot tube accessory but it doesn't say how fast it will read and they also bluetooth to phones and tablets.

    https://www.testo-direct.ca/product/...sure-manometer

    PM me and I can send you a link to another forum that these were discussed and why they don't work.


  8. #8
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    The hot wire anemometer type work well but you need to measure in multiple spots across the diameter. It seems like there is no real easy way to measure air speed. As noted above, you should also take static pressure readings at the same time you do air speed.

    The fan anemometer just doesn't do an accurate job and typically gives high readings.

  9. #9
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    I would recommend a hot wire anemometer and read up on how to do a duct traverse. That will work well for what we are checking. If you want a little more accuracy also get a magnehelic and a pitot tube to measure static and total pressure. That takes some math but it isn't to difficult.

  10. #10
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    It is unfortunate that it is so difficult to take good measurements on a dust collection system. Using a hot wire anemometer and doing a traverse properly takes time a money. If it were easier, then understanding the effects of making changes to your system would be easier.

    I use a digital static pressure gauge and a good performance curve for your dust collector. You can measure the static pressure and then use the curve to estimate the cfm. Wood Magazine has provided some pretty good performance curves for a number of dust collectors.

  11. #11
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    Quote Originally Posted by Larry Frank View Post
    If it were easier, then understanding the effects of making changes to your system would be easier.
    But that would take all the fun out of it.

    Quote Originally Posted by Larry Frank View Post
    I use a digital static pressure gauge and a good performance curve for your dust collector. You can measure the static pressure and then use the curve to estimate the cfm.
    I do have a copy of the manufacturer's specs. And there's a performance curve at the end of the sheet, But I'll have to do a little more research on using the curve with a digital static pressure gauge?
    https://www.cincinnatifan.com/catalo...ors108-sls.pdf
    The collector I have is the 200S 2HP 3-phase model.

    The main reason for trying to figure out my air flow is because I plan to convert my barrel mounted dust collector into a cyclone style system. Part of that problem is trying to figure out what size cyclone & inlet/outlet ducts to use?

    I don't really care about the exact cfm numbers & readings being high "like with the fan style units"
    just as long as I can establish a base-line/ball-park measurement to help somewhat figure things out.

    Part of my problem/confusion is with the current 7" dia. inlet & 6" outlet in my blower's housing!
    Most of the cyclone units designed to match my blower's stated maximum 1100 cfm have either a 4" or 5" inlet/outlet. I realize that changing the original design of the dust collector will effect the overall performance, But knowing the base-line difference in air flow & static pressure between the 7" opening & the various duct sizes should help me decide what size cyclone to get.

    Doug

  12. #12
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    Hi Doug, a 4" inlet on a dust collector will be about 400CFM, a 5 inch will be in the 600CFM range.

    My 1.5 HP cyclone has a 6" inlet and is rated at 957 CFM at 0" water column, and 700 CFM at 4" WC.

    You'll need a cyclone with a 7 or 8 inch inlet...........Regards, Rod.

  13. #13
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    Many times the mfg ratings are an exaggeration. I doubt that a 1.5 hp Dust Collector pulls 957 cfm.

    I have measured 700 cfm with a 4" port with my system. How many cfm you can pull thru a 4" port depends also on the dust collector you are using.

  14. #14
    I have a fan style anemometer and if used to compare losses in percentages I think it works just fine if it is held the same way for each measurement.
    A simple homemade static pressure meter is also very good to see how adding to the system adds airflow resistance.
    If nothing but absolute and accurate airflow numbers are required there's really no way around spending the money to get the equipment and spending the time to learn how to make the measurements.

  15. #15
    Quote Originally Posted by Larry Frank View Post
    Many times the mfg ratings are an exaggeration. I doubt that a 1.5 hp Dust Collector pulls 957 cfm.

    I have measured 700 cfm with a 4" port with my system. How many cfm you can pull thru a 4" port depends also on the dust collector you are using.
    What if I told you I am pulling 2000 CFM on 5” port? Would you say I’m out to lunch?

    So, in this video I am using a 5” blast gate with a 5” flex hose reduced to 4 inch ABS...stepped back up to 6 inch ductwork then into the bucket and then into 10.5 inch ID sono tube. Let the metre show what it’s reading. What is the airspeed through the 4 inch ABS, (you’ll have to do some calculations here)??? Internal ABS which is 4 inches is 4 inches. Is it possible to have 2200 ft/m on through only 4 inches? What is 2200ft./m calculated 10.5 inches stepped down to through 4 inch ABS, in CFM???
    https://www.youtube.com/watch?v=SB9Bt23iYBY
    Last edited by Matt Mattingley; 12-28-2018 at 2:09 AM.

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