Checking CFM Of A Dust Collector

[Doug Walls]

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

[John K Jordan]

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/Cyclone/measurement.cfm

JKJ

[Peter Christensen]

https://www.testo-direct.ca/product/testo-405i-smart-and-wireless-hot-wire-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.

[Doug Walls]

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

[Doug Walls]

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

[David Justice]

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/B019HR4LTW/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

[Peter Christensen]

"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/testo-510i-smart-and-wireless-differential-pressure-manometer

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

[Larry Frank]

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.

[Mark Paavola]

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.

[Larry Frank]

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.

[Doug Walls]

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. :D


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/catalogs/DustCollectors108-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

[Rod Sheridan]

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.

[Larry Frank]

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.

[Charlie Hinton]

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.

[Matt Mattingley]

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

[Mike Chalmers]

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.

+ a Gazillion for this. If you want to be a purist, you better have deep pockets. Providing Relative information that allows one to guage the effectiveness of additions, modifications, changes, need not be an expensive exercise. Boils down to ROI, Return on Investment. Is it really worth the expense? According to the experts and purists, we are never going to get it "right" anyway.

[Larry Frank]

The way I calculate given the video, you are about 2200 fpm on a cross section of about .60 square ft. or about 1300 cfm. That is very high for a 4" port. What dust collector are you running - hp and impeller size?

I can not get that with a 5 hp motor and 15" impeller.

[Larry Frank]

I do not want to be a purist but want numbers that I can believe. A fan anemometer provides some highly variable numbers depending on the placement of it from the mouth of the duct. I did an experiment where I used a fan anemometer on a 4" duct and mounted it securely at several distances from the mouth of the duct. The results I obtained are shown in the graph. It is extremely difficult to hand hold one in the same place every time that you do a test. Any differences in how you hold it will result in fairly large differences in air speed.

399689

I think that the best, cheapest, and most accurate way to determine performance is by measuring the static pressure. You can either build your own water-tube one or buy a digital one. You can see any changes to your system by looking at differences in pressure. You can also look at a curve like those that Wood Magazine did to estimate the flow from the pressure. The graph below is from Wood Magazine testing 1.5 and 2 hp dust collectors.

399690

[John K Jordan]

...
I think that the best, cheapest, and most accurate way to determine performance is by measuring the static pressure. You can either build your own water-tube one or buy a digital one.

Larry,

Your advice on these topics has always been excellent. Thanks!

Can you recommend a digital meter? I see this inexpensive differential l meter on Amazon. Does it look useful?
https://www.amazon.com/d/Manometers/Rupse-Hand-held-Differential-Barometer-Professional/B06WP2Y9VY/ref=sr_1_5?ie=UTF8&qid=1546005758&sr=8-5&keywords=water+tube+manometer

Any recommendations if someone wanted to buy a water tube? How about this one?
https://www.amazon.com/Yellow-Jacket-78075-Water-Manometer/dp/B0038QHTK2/ref=sr_1_3?ie=UTF8&qid=1546005992&sr=8-3&keywords=water+tube+manometer

JKJ

[Larry Frank]

I have a UEi EM151 which just measures static pressure and not available anymore. The one you picked can measure differential pressure and with the right probes can be used to measure flow also.

The water manometer you referenced will work or build your own. There are lots of instructions on YouTube. I built my own.

399694

[Matt Mattingley]

The way I calculate given the video, you are about 2200 fpm on a cross section of about .60 square ft. or about 1300 cfm. That is very high for a 4" port. What dust collector are you running - hp and impeller size?

I can not get that with a 5 hp motor and 15" impeller.
Yeah, Larry I was thinking it was around 1322 CFM. I never thought that was crazy high. I’m running just a homemade BP cyclone and just a homemade impeller that is 17 1/4 inches I did get a little inventive building it. The impeller, I built as a two stage. I have no clue if this is improving the performance. I did a whole thread on it. 5hp. Motor.
https://sawmillcreek.org/showthread.php?220526-Bill-Pentz-cyclone-build&highlight=

With the system completely closed it is pulling 19 3/4” WC. One day soon I want to complete a full fan curve chart with amperage draw.
399725 399726 399727
No clue why the pictures are showing up sideways.

[Larry Frank]

That is a very large impeller and it would be interesting to see a performance curve. It takes a lot of effort to get the data. I posted a couple of threads that showed how I did mine and used a hot wire anemometer with appropriate did positions across the duct. I did a lot of repeat measurements.

I just do not trust the fan type anemometer to get anywhere near accurate results. With the effort you put in to build your own system, I think it would be worthwhile to get accurate measurements.

[Matt Mattingley]

That is a very large impeller and it would be interesting to see a performance curve. It takes a lot of effort to get the data. I posted a couple of threads that showed how I did mine and used a hot wire anemometer with appropriate did positions across the duct. I did a lot of repeat measurements.

I just do not trust the fan type anemometer to get anywhere near accurate results. With the effort you put in to build your own system, I think it would be worthwhile to get accurate measurements.
Why do you not trust the fan type Aneometer? I understand how it can increase pressure due to its design. But sometimes I like to keep things simple. A simple fan does a very accurate measurement if you’re not closing off the complete duct work. In my case I increased the ductwork to 10.5 inches and interrupted some of the airflow with a 3 inch dia. fan testing device. I do think the impact pressure would be very minimal. I think the static pressure with the added 8 foot pipe could be a balance factor.

My fan impeller design might be the interesting factor. The blower was built very closely to Bill Pentz’s design except for the fan impeller and height of the blower and impeller. I used his 16 inch blower design. And I jammed a 17 1/4 inch blower in there with (I think) 3/8 clearance to what I think is called fulcrum. I think Bill had it set at 1”. I believe I only gave a quarter inch clearance top and bottom from the impeller to the blower walls. Don’t get me wrong, I’ve measured The decibel sound reading (not professionally just using an iPhone app) but… It comes in way higher than any advertised purchased unit. I had a 1.5 horse power somewhat portable dc unit with maybe a 13 inch impeller. Sometimes I found my Rigid shop vac or my 1980s double blower garbage pail DC unit better. When I was done building this DC unit I tested almost 112 A on start up, 19 A at full flow through the 6 inch main duct and about 12 A with all blast gates closed.

When I did my testing with no ductwork and the 40 in.³ intake I was pulling 23 A on my 23 amp motor. When I reduced the intake to 6 inch diameter I found 19 apps to draw on the motor. I restricted it by 12 in.³. If I knew then what I know now, I probably would’ve run 7 inch duct. But, I’m not planning to going to go backwards unless I arequire a machine that needs tons of CFM. I have tested somewhat reluctantly using a junkie test metre on my 6 inch main, and I was pulling over 10,000 ft./m. It was only rated for 6000 ft./m.

My future dream is to add a overhead filter duct with replaceable filters, always pulling maybe 100 to 200 CFM.

[Bill Dufour]

Do folks really care about the flow rates or just relative differences with new configurations. Seems to me a propeller type is cheapest and accurate enough with good repeatability? Please correct me if I am wrong.
BTW what kind of mph speeds do dc's run?
Bill D

[Matt Mattingley]

Do folks really care about the flow rates or just relative differences with new configurations. Seems to me a propeller type is cheapest and accurate enough with good repeatability? Please correct me if I am wrong.
BTW what kind of mph speeds do dc's run?
Bill D
in the main trunk, 50-60ish mph keeps main trunk clear. Branches should be sized for each machine on cfm on machine requirements. You can’t pull more cfm than than than the main trunk, always less due to static pressures.

[Larry Frank]

It all depends on what you want to know. A fan type anemometer is certainly cheap. As far as accurate and repeatable, not for me but maybe for you.

I originally felt like some who thought it was great. I did a bunch of testing with one and found it highly variable depending on how you hold it. I posted my results of testing varying the distance of the fan anemometer to the end of a duct earlier in the thread. The results are dependent not only on the distance but the angle and where you hold it. In addition, the air causes it to move around.

If you want to get even more details, go over to the Aussie Woodwork Forums in the Dust Extraction sub forum. BobL goes into great detail about all things of measuring cfm in dust collection.

I will say one last time that the easiest way to estimate performance is to use a manometer to measure pressure and then use a published performance curve to estimate cfm. I built my own performance curve for my system and when I want to know cfm, I use a digital manometer to get pressure and then read a curve.

I would love to see some data that shows using a fan anemometer for measuring dust collector performance is accurate. I am not going to discuss this any further as I have done enough testing of one to know how inaccurate they are. However, please measure your system any way that makes you happy.

[Peter Christensen]

Here is a paper that talks about fan type anemometers. It was posted on another forum and while not specific to dust collection it does point out the problems with them.

https://www.cdc.gov/niosh/mining/userfiles/works/pdfs/ri9061.pdf

[Larry Frank]

There is a current discussion on the Aussie forum on the vane anemometer that is worth reading.

Woodwork Forums sub Dust Extraction

It points out that measuring at the mouth of a duct has issues due to the turbulence generated at the mouth.

[David Kumm]

Impeller diameter, blade design and housing design are all critical in delivering cfm under pressure. Look at the Cincinnati fan tables for cfm at pressure per hp for various fan sizes and designs. The table for New York and Chicago fan are very similar. I think the op would spend money better saving for a larger motor and impeller. A cyclone adds 2-4" SP to a system and while a 2 hp cyclone may turn out to be adequate, I'm betting when you measure it will just quantify the number behind a marginal at best system. Good numbers are good to know ( I'm a numbers guy ) but I've also worked with systems from 2-7.5 hp and radial and BC impellers of various diameters and I use the numbers more to show improvement at higher pressures rather than on an absolute basis. After experimenting with a bunch of systems, I consider a 3 hp 14" impeller to be the minimum cyclone with 15" and 5 hp a more safe bet. If I'm limited to 2 hp or maybe even 3 hp, I'll generally stay with a bagger with oversize singed poly bags as I'd rather have more cfm and most 14" BC impellers are low pressure and suffer from the preseparator pressure cost. Diameter is huge when dealing with a BC impeller. Not so much with a radial. Dave

[Doug Walls]

I think the op would spend money better saving for a larger motor and impeller.
I've thought about that, But the blowers design looks to be closely matched to the impeller.
The current impeller is 12-1/4" & there's only about 3/4" clearance at the closet point.

The last two pics have a black marker line that was drawn with the impeller placed in position.

Doug

[Doug Walls]

I consider a 3 hp 14" impeller to be the minimum cyclone with 15" and 5 hp a more safe bet.
Although it sure would be nice to have a larger DC!

Currently with only a 40-amp 220 supply to my two car garage, I'm sort of limited as far as power goes.


( I'm a numbers guy )
Here's some numbers for you!

5hp. Rotary Phase Converter FLA 14.8
2hp-3ph. Dust Collector FLA 5.2
2hp-3ph. Dewalt Radial Arm Saw FLA 5.0

I've never actually tried running all three of these together yet! But in theory it should work?

Figuring that the RPC idler motor should probably never draw it's rated FLA (except for start-up)
it should give me a little wiggle room.

Although math was never really my favorite subject! Using the FLA of 25amps listed above, And figuring that the 3 separate power lines are being generated by the two regular 220 volt input lines.
Working with the numbers, The square root of 3 (1.732) X 25Amps = 43.3 amps.

Doug

[Matt Mattingley]

Although it sure would be nice to have a larger DC!

Currently with only a 40-amp 220 supply to my two car garage, I'm sort of limited as far as power goes.


Here's some numbers for you!

5hp. Rotary Phase Converter FLA 14.8
2hp-3ph. Dust Collector FLA 5.2
2hp-3ph. Dewalt Radial Arm Saw FLA 5.0

I've never actually tried running all three of these together yet! But in theory it should work?

Figuring that the RPC idler motor should probably never draw it's rated FLA (except for start-up)
it should give me a little wiggle room.

Although math was never really my favorite subject! Using the FLA of 25amps listed above, And figuring that the 3 separate power lines are being generated by the two regular 220 volt input lines.
Working with the numbers, The square root of 3 (1.732) X 25Amps = 43.3 amps.

Doug
Doug, I am not so much a numbers guy, but I’ll play... First, do you really have 220v in MI??? Please test! With picture please.

Is the RPC considered a motor or generator under the NEC?
2hp + 2hp (3ph)=4hp. 3ph.
4hp A (3ph) at V/1.73= ?
I would be interested to see a clamp on metre “read” prior to 40 amp circuit showing amp draw, with RPC, DC & RAS all on line with picture.

Remember I am not a numbers guy. But... I am a picture guy.

[Doug Walls]

Doug, I am not so much a numbers guy, but I’ll play... First, do you really have 220v in MI???
The power here is generally referred to as 110/220, But the actual voltage is usually slightly above 120 and 240!

Here's the power reading at my RPC.

Doug

[Doug Walls]

Is the RPC considered a motor or generator under the NEC?
I don't know for sure, But being it "draws" power to create the third leg I'm guessing it's considered a motor?


I would be interested to see a clamp on metre “read” prior to 40 amp circuit showing amp draw, with RPC, DC & RAS all on line with picture.
Well that's probably not going to happen for a while yet! I need to finish running the conduit & outlets from my RPC, Probably a project for this spring.

For now I'm mainly interested in getting the DC set-up & installed!
The DC will be going in the corner of the garage & I'm thinking of trying to partially enclose it to help quiet it down a little.

Doug

[Matt Mattingley]

Thanks Doug. Almost everywhere in North America it is a split Phase 120/240+-5% residential.

You’re 40 amp circuit will be just fine. This is not a clamp on metre but a metre that I have on the wall just for quick reference. The numbers are very close to my clamp on.

Hopefully the pictures don’t get jumbled.
I started the 5hp RPC(disregard the small amperage read on the three phase meter. There’s a small transformer that’s online)
Then 1hp mill
Then 1 hp grinder
Then 1.5 hp bandsaw
Then half horsepower bandsaw
Then 2 hp grinder
Then 1hp hydraulic pump

Nothing has load on it. All fed from 40 amp 240 V circuit.

400377400378400383400379400380400381400382

And here’s a picture of my big 4hp disc sander online (by itself with the 5 hp RPC).
400384

[Ole Anderson]

Not looking for lab grade equipment or results. Here is what I use: Here I am measuring 570 cfm at the inlet of my Rockler DustRite connector. 6016 fpm on a 4.12" opening. I was reading 7" WC at the inlet to my 2 hp SDG.

[Larry Frank]

Fan anemometers used like that are very inaccurate and over rate the cfm.

[Ole Anderson]

Fan anemometers used like that are very inaccurate and over rate the cfm.

Any data to back that up and to put a number to accuracy range or are you repeating what someone else said? Probably not any less accurate than the fan curves supplied by the manufacturers.

[Peter Christensen]

Any data to back that up and to put a number to accuracy range or are you repeating what someone else said? Probably not any less accurate than the fan curves supplied by the manufacturers.

It was stated in the paper I linked in post #27.

[Larry Frank]

I have posted on here the variation that I measured with a fan anemometer at the end of a 4" duct. I have measured mine with a hot wire anemomete and posted curves for it.

I absolutely am not just repeating what someone told me. I actually did the measurements.

As for the mfg curves... There are some that I do not trust. However, I have taken the time to measure my dust collector and find the mfg curve to be reasonably accurate. I have also read the procedures that some mfg have used and they are reasonable. I have also taken the time to compare some of the mfg curves to those done by Wood Magazine and again find that some mfg data is pretty good. Some not so good and an exaggeration. You need to read the fine print about how some of the max flows are measured.

So, what have you done to research the accuracy of curves or are you repeating what others have said.

I have done my research and studies and confident in my methods and results. I use my own data and curves to monitor and improve my system.

[John K Jordan]

...I have done my research and studies and confident in my methods and results. I use my own data and curves to monitor and improve my system.

Larry, I can add that your posts on these things have always been obviously well-researched and complete. I appreciate the time you've put into testing and verification and your willingness to share your experience with we-the-clueless!

JKJ

[Ole Anderson]

I have posted on here the variation that I measured with a fan anemometer at the end of a 4" duct. I have measured mine with a hot wire anemomete and posted curves for it.

I absolutely am not just repeating what someone told me. I actually did the measurements.

As for the mfg curves... There are some that I do not trust. However, I have taken the time to measure my dust collector and find the mfg curve to be reasonably accurate. I have also read the procedures that some mfg have used and they are reasonable. I have also taken the time to compare some of the mfg curves to those done by Wood Magazine and again find that some mfg data is pretty good. Some not so good and an exaggeration. You need to read the fine print about how some of the max flows are measured.

So, what have you done to research the accuracy of curves or are you repeating what others have said.

I have done my research and studies and confident in my methods and results. I use my own data and curves to monitor and improve my system.

Larry, thank you, you answered my question. I must have skipped over post #27. I did look at that and came away with the conclusion that the high speed fan anemometer used in the research overstated flow in 4-6" ducts by about 20%. As far as fan curves, I used the American Woodworker Magazine 2008 article as as somewhat of a benchmark when comparing dust collectors prior to my purchase. The Wood magazine article came out just after my purchase. While not lab conditions, the tests were conducted in a consistent manner between the different dust collectors and therefore had validity in my mind. I did compare their results with a three different manufacturer's published curves, and IIRC some were within 20%, others well outside of that 20% number. Having trouble finding that article at the moment. Oneida had two different fan curves for my 2 hp SDG at the time. The one they settled on agrees fairly closely with my measurements, of course that is based on my anemometer flow results.