cheesewonton
Well-known member
Lol, I just retired from a career in one of the Navy's premier weapons labs. I made a career in R&D. I think I know my way around instruments and data.
Measuring CFM?
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cheesewonton
Well-known member
With the GM8901 to obtain an accurate airflow measurement you would multiply the speed in feet per minute by the area of the hose opening in square feet. Hoses have different diameters and thus different surface areas at the opening, so there is no one size fits all factor. If you are measuring a 1 1/4 inch diameter hose you would multiply the observed airspeed in ft/min times the surface area 0.0088 square feet. If you were measuring a 35mm hose on something like a Miele you would multiply the observed airspeed in ft/min by 0.0104. Ect. Each hose diameter will have a different square foot opening to use in the calculation.
Likewise with the HP-846A, directly from the operating manual, you have to manually enter the surface area of the hose opening of the vacuum being tested. If you are not entering the correct value the resulting CFM calculation will be incorrect. As before for accuracy there is no one size fits all factor to multiply airspeed by.
A general shortcoming with rotating vane anemometers are bearing friction and the amount of obstruction to airflow inherent in their design. Hot wire anemometers, like you find in automobile Mass Airflow Sensors do not create as much of an obstruction to the airflow so there are less losses and greater accuracy. HVAC pros will use capture hoods with differential pressure sensors or a thermal ( hot wire ) sensor.
Likewise with the HP-846A, directly from the operating manual, you have to manually enter the surface area of the hose opening of the vacuum being tested. If you are not entering the correct value the resulting CFM calculation will be incorrect. As before for accuracy there is no one size fits all factor to multiply airspeed by.
A general shortcoming with rotating vane anemometers are bearing friction and the amount of obstruction to airflow inherent in their design. Hot wire anemometers, like you find in automobile Mass Airflow Sensors do not create as much of an obstruction to the airflow so there are less losses and greater accuracy. HVAC pros will use capture hoods with differential pressure sensors or a thermal ( hot wire ) sensor.
vaclab
Well-known member
cheesewonton,
I simply had to respond to such a grossly ignorant comment. While I have GREAT respect for our armed forces, if what you claim is true, you couldn't pass an 8th grade Algebra or 9th grade Geometry test. Geez, what a disappointment. I posted these calculations many years ago on Vacuumland, but here they are again.
For the GM8901 anemometer:
Diameter of GM8901 Anemometer Detector = 2.1875 inches
Radius = 1.09375 inches = .0911458 feet
Detector Area = 3.1415926 x .0911458 x .0911458 = 0.0260990 (rounded)
Soooo, if I obtain a reading of say 5747 ft/min, that converts to about 150 CFM.
5747 (ft/min) x 0.026099 (area) = 149.9 CFM
I also noticed you refused to provide ANY of your lab specs after I stated mine (as expected). No pics, no vids, just false claims. Par for the course I suppose.
Lastly, you did mention a 9.5 on the Baird meter, which equates to 109 CFM. And you somehow can't manage to clean (dust) with 109 hose CFM? What world do you live in anyway? The typical hose CFM is around 80 CFM, so your Kirby has plenty of above the floor cleaning power.
Bill
I simply had to respond to such a grossly ignorant comment. While I have GREAT respect for our armed forces, if what you claim is true, you couldn't pass an 8th grade Algebra or 9th grade Geometry test. Geez, what a disappointment. I posted these calculations many years ago on Vacuumland, but here they are again.
For the GM8901 anemometer:
Diameter of GM8901 Anemometer Detector = 2.1875 inches
Radius = 1.09375 inches = .0911458 feet
Detector Area = 3.1415926 x .0911458 x .0911458 = 0.0260990 (rounded)
Soooo, if I obtain a reading of say 5747 ft/min, that converts to about 150 CFM.
5747 (ft/min) x 0.026099 (area) = 149.9 CFM
I also noticed you refused to provide ANY of your lab specs after I stated mine (as expected). No pics, no vids, just false claims. Par for the course I suppose.
Lastly, you did mention a 9.5 on the Baird meter, which equates to 109 CFM. And you somehow can't manage to clean (dust) with 109 hose CFM? What world do you live in anyway? The typical hose CFM is around 80 CFM, so your Kirby has plenty of above the floor cleaning power.
Bill
vaclab
Well-known member
Here we go again. If you had bothered to read/understand my previous posts and/or view some of my extensive YouTube videos, you would clearly see the cone adapters I use. These type of adapters have been used in the industry for decades. They adapt (without interference) diameter "A" to diameter "B" very easily. Try and make one rather than whining so much. How on Earth do you think that airflow measurements were made say, 50 years ago?
Example #1: if a hose is 1" diameter and you want to measure its flow, you can with any measuring tool that is 1" or larger. Yup, you can create a 1" to 2" cone adapter and proceed to mate it to a 2" vane.
Example #2: if you have a large 12" tube/square (say an A/C vent), you can use the same 2" vane detector to measure part of the area (say 10%), then multiply by 10.
Example #1: if a hose is 1" diameter and you want to measure its flow, you can with any measuring tool that is 1" or larger. Yup, you can create a 1" to 2" cone adapter and proceed to mate it to a 2" vane.
Example #2: if you have a large 12" tube/square (say an A/C vent), you can use the same 2" vane detector to measure part of the area (say 10%), then multiply by 10.
cheesewonton
Well-known member
You are multiplying airspeed in ft/min times 0.26099. That is the diameter of the fan. You are using the instrument incorrectly. You need to multiply airspeed by the diameter of the hose opening. The operators manuals for both anemometers ( I looked at them ) tell you to multiply airspeed by the surface area of the duct. In this case the duct is a vacuum hose. This explains your overly high airflow readings. That is also how my anemometer explains the airflow calc.
Last edited:
vaclab
Well-known member
Here we go again...and you typed 0.26099 instead of 0.0260990. Different by a factor of 10. So here's a picture of the least expensive way to measure vacuum airflow (i.e. the hose is smaller than the vane). Note: my wife isn't holding everything exactly straight.
The vane is a detector and the cone (properly sealed at both ends of course) will spin at a speed proportional to the flow at its given diameter. That same airflow enters the hose at a different diameter. The total flow of the air MUST be the same (minus about 0.25 CFM for the blade drag of the GM8901). Sooo, if 100 CFM enters the vane, 100 CFM MUST enter the hose.
One method of using a small vane to calculate airflow in a larger airduct is to first find the area of the duct (i.e. H x W). Find out the ratio of duct area divided by vane area and now you have a simple multiplier you can store in your head.
For example: if the area of the duct is 10 times the area of the vane, simply take your (calibrated CFM) measurement and multiply by 10. Say the vane reads 10 CFM, then the total airflow through the duct would be 100 CFM. Pretty easy huh?
Do you require another picture showing the vane being held up to a duct (area comparison)?
The vane is a detector and the cone (properly sealed at both ends of course) will spin at a speed proportional to the flow at its given diameter. That same airflow enters the hose at a different diameter. The total flow of the air MUST be the same (minus about 0.25 CFM for the blade drag of the GM8901). Sooo, if 100 CFM enters the vane, 100 CFM MUST enter the hose.
One method of using a small vane to calculate airflow in a larger airduct is to first find the area of the duct (i.e. H x W). Find out the ratio of duct area divided by vane area and now you have a simple multiplier you can store in your head.
For example: if the area of the duct is 10 times the area of the vane, simply take your (calibrated CFM) measurement and multiply by 10. Say the vane reads 10 CFM, then the total airflow through the duct would be 100 CFM. Pretty easy huh?
Do you require another picture showing the vane being held up to a duct (area comparison)?
cheesewonton
Well-known member
That is incorrect. The diameter that matters is the diameter of the hose opening. My anemometer is a simple probe. There is no shroud like the propeller ones. You don't use an adapter cone. Just hold the probe in front of the hose with the probe oriented for the direction of airflow ( a dot on the top of the probe gives you orientation ).
For use measuring airflow for an HVAC situation the technique is to take airspeed measurements in feet per minute at the four corners of a duct and at the center, then average those readings. If it is a round duct like my house has you would take readings at four of five points around the perimeter and at the center and calculate their average. Take the average airspeed you just calculated and multiply that by the area of the duct in square feet. For a smaller duct like a vacuum hose you do the same, but you have a smaller duct. But the salient area is the area of the duct, which is the hose opening.
When an HVAC tech takes an airflow measurement using a shrouded airflow meter they too use the surface area of the duct opening, not the smaller opening of the shroud, to calculate airflow. Look at some of the CFM figures shown at the beginning of this thread. The CFMs shown for the suction inlet of the vacuum are literally greater than the motors in them can produce based on the performance charts supplied by the manufacturers. These airflow values are literally impossible for those vacuums to achieve. The numbers I calculate are less than the maximum values for a given orifice size, which makes sense given airflow losses going from the motor to the hose end.
cheesewonton
Well-known member
Attached is the manual for my anemometer. Read page 4. It explains how to determine airflow.
vaclab
Well-known member
You're simply not grasping how measuring tools work here. You should know that your hot wire doesn't actually measure airflow directly just like a vane type. It measures airspeed and then you enter in the area calculation (and type, i.e. square, round). Hot wire anemometers also have to constantly correct for temperature and humidity since the wire has to report a temperature difference via voltage/resistance. Also, how the hot wire thermometer is used will affect the readings. For example, stuffing it straight into the flow versus a vertical position. The vane type is only used one way, which simplifies things somewhat.
The vane type only cares about the air flowing through itself, not the hose or airflow box hole, etc. That's a known calculation and is given above. Then, various cones are used translate the flow to the vane in the proper manner and thusly CFM is measured.
Let me say it another way. I have gathered and created data from many OEM's and not only compared them to my readings but also have been the actual SOURCE of verification for some of those OEM's as well. In other words, My measurements stand confirmed as accurate, even by third parties. I've even compared notes with the likes of Wirecutter (see my YouTube video).
To be used correctly, a hot wire thermometer must be calibrated with various known wind sources and I'll let you Google that for verification.
The vane type doesn't care about temperature or humidity and usually needs no extra calibration.
Bottom line, your false assumption that vane types are worse (not to be trusted) compared to hot wire types is quite disappointing.
Now onto duct measurements:
My simple example was exactly that. Something that assumes an area and approximately equal flow at all points in the space. I have no desire to type a dissertation length post. Obviously, with things like corrugations, angles, vents, splitters, turbulence is introduced.
Airflow CFM Measured with a Hot Wire Anemometer!
If you watch carefully, you see the tech perform a wide range of measurements that involve a HUGE amount of human error (speed of insertion/removal, tilting, etc. Then everything has to be averaged, yippee! While this method will certainly give a general measurement of airflow, I hope you see just how sloppy the entire procedure is. What would the error bar calculations be, plus or minus 10%? Larger? Not to mention performing measurements with several open holes, geez!
Anyway, good luck with your measurements but unless you make the attempt to fully verify them (as I have for years), your results won't gain any credibility.
Bill
The vane type only cares about the air flowing through itself, not the hose or airflow box hole, etc. That's a known calculation and is given above. Then, various cones are used translate the flow to the vane in the proper manner and thusly CFM is measured.
Let me say it another way. I have gathered and created data from many OEM's and not only compared them to my readings but also have been the actual SOURCE of verification for some of those OEM's as well. In other words, My measurements stand confirmed as accurate, even by third parties. I've even compared notes with the likes of Wirecutter (see my YouTube video).
To be used correctly, a hot wire thermometer must be calibrated with various known wind sources and I'll let you Google that for verification.
The vane type doesn't care about temperature or humidity and usually needs no extra calibration.
Bottom line, your false assumption that vane types are worse (not to be trusted) compared to hot wire types is quite disappointing.
Now onto duct measurements:
My simple example was exactly that. Something that assumes an area and approximately equal flow at all points in the space. I have no desire to type a dissertation length post. Obviously, with things like corrugations, angles, vents, splitters, turbulence is introduced.
Airflow CFM Measured with a Hot Wire Anemometer!
If you watch carefully, you see the tech perform a wide range of measurements that involve a HUGE amount of human error (speed of insertion/removal, tilting, etc. Then everything has to be averaged, yippee! While this method will certainly give a general measurement of airflow, I hope you see just how sloppy the entire procedure is. What would the error bar calculations be, plus or minus 10%? Larger? Not to mention performing measurements with several open holes, geez!
Anyway, good luck with your measurements but unless you make the attempt to fully verify them (as I have for years), your results won't gain any credibility.
Bill
cheesewonton
Well-known member
All I can say is I asked the manufacturer how to use the device to measure airflow from vacuum cleaners and use it the way the manufacturer described. I e-mailed the for advice before forking out that much money to be sure it was the right tool for the job. The meter has a temperature compensation but not one for humidity. As a long time military and civil helicopter pilot before going over to the weapons side of the Navy as an Operations Research Analyst I can tell you with absolute assurance anything with a propeller lives and dies on density altitude. What is that? Air density corrected for altitude, temperature and humidity. That vane type airflow meter is very much affected by all three.
As I said before some of the airflow numbers shown on this site are beyond the capabilities of the motors in the vacuums tested. They are simply not possible. There is no suction motor made for an old Tristar CXL that will deliver over 130 cfm at the hose opening. None. Suction motors that fit into a CXL and draw ten amps under ideal conditions will pull somewhere in the high 70s to high 80s cfm through a 1.125 inch orifice with no other restriction. That is the best anyone can expect at the hose connection of a Tristar. Expect even less at the hose end. The ten amp motor, Ametek 115923, is rated at 122 cfm max at a wide open orifice. When I see a post showing airflow in excess of 130 cfm I know with certainty there is an error. This comes from literally decades of working with numbers.
Something drilled into me since junior high math classes is to look at your solution and ask if it is reasonable. Same throughout my undergraduate and graduate classes where the math became far more complicated and all throughout my professional life. I know Vaclab is upset that I called out his technique but I stand by mine. I have been hided enough in peer reviews / murder boards of my own work to be careful what I put forth in terms of calculations and make sure my own numbers are reasonable. 50 something cfm at the end of a hose on a Tristar makes sense. Over 100 cfm from that small an orifice at the end of a hose with all the loses due to restrictions along the way does not make sense.
Vaclab, before you layer more criticism on me please familiarize yourself with the actual performance the suction motors in these vacuums are capable of. I am going to attach the Ametek performance bulletins for the OEM motor in a Tristar CXL or DXL , 116884-49, and one for the Ametek 115923, the typical ten amp two stage motor people retrofit to these old vacuums. I will also add a bulletin for the higher performance 11 amp motor used in Pro Team backpack vacuums, 119347-01, that I have used in Tristars in the past. It is slightly higher performance than 115923. The interesting thing about Tristars is that regardless of which of the three motors I use the result at the hose end is a constant, boring 52 cfm.
On these performance bulletins look at the rated airflow for a 1.125 inch orifice. If your instruments are showing significantly more than the motor is rated for you are probably doing something wrong and need to re-evaluate your procedure.
As I said before some of the airflow numbers shown on this site are beyond the capabilities of the motors in the vacuums tested. They are simply not possible. There is no suction motor made for an old Tristar CXL that will deliver over 130 cfm at the hose opening. None. Suction motors that fit into a CXL and draw ten amps under ideal conditions will pull somewhere in the high 70s to high 80s cfm through a 1.125 inch orifice with no other restriction. That is the best anyone can expect at the hose connection of a Tristar. Expect even less at the hose end. The ten amp motor, Ametek 115923, is rated at 122 cfm max at a wide open orifice. When I see a post showing airflow in excess of 130 cfm I know with certainty there is an error. This comes from literally decades of working with numbers.
Something drilled into me since junior high math classes is to look at your solution and ask if it is reasonable. Same throughout my undergraduate and graduate classes where the math became far more complicated and all throughout my professional life. I know Vaclab is upset that I called out his technique but I stand by mine. I have been hided enough in peer reviews / murder boards of my own work to be careful what I put forth in terms of calculations and make sure my own numbers are reasonable. 50 something cfm at the end of a hose on a Tristar makes sense. Over 100 cfm from that small an orifice at the end of a hose with all the loses due to restrictions along the way does not make sense.
Vaclab, before you layer more criticism on me please familiarize yourself with the actual performance the suction motors in these vacuums are capable of. I am going to attach the Ametek performance bulletins for the OEM motor in a Tristar CXL or DXL , 116884-49, and one for the Ametek 115923, the typical ten amp two stage motor people retrofit to these old vacuums. I will also add a bulletin for the higher performance 11 amp motor used in Pro Team backpack vacuums, 119347-01, that I have used in Tristars in the past. It is slightly higher performance than 115923. The interesting thing about Tristars is that regardless of which of the three motors I use the result at the hose end is a constant, boring 52 cfm.
On these performance bulletins look at the rated airflow for a 1.125 inch orifice. If your instruments are showing significantly more than the motor is rated for you are probably doing something wrong and need to re-evaluate your procedure.
cheesewonton
Well-known member
A couple of news stories with excellent videos about the place I just retired from. We used to do some really cool videos for public release but people up the chain of command came to the opinion we were sharing too much information so since 2018 no more "Greatest Hits" videos. If you want to poke around Youtube you can find a whole series of videos called "Pictures of US" that depict China Lake going back to its inception in 1943.
I highly recommend watching the videos. The one showing a parachute test was for NASA. We did the parachute descent systems for several recent Mars landers. And yes the tow vehicles pulling the trucks getting blown up are unmanned remote controlled O_O
https://www.twz.com/25281/what-its-...cretive-china-lake-weapons-development-center
https://www.twz.com/24940/weapons-t...e-everything-in-this-crazy-greatest-hits-reel
I highly recommend watching the videos. The one showing a parachute test was for NASA. We did the parachute descent systems for several recent Mars landers. And yes the tow vehicles pulling the trucks getting blown up are unmanned remote controlled O_O
https://www.twz.com/25281/what-its-...cretive-china-lake-weapons-development-center
https://www.twz.com/24940/weapons-t...e-everything-in-this-crazy-greatest-hits-reel
blackheart
Well-known member
This is like watching the two smart kids with different answers arguing....
I'm going to play Devil's advocate here and ask this question. When we place machines like Kirbys or Royals onto our airflow boxes and the opening from said airflow box is 2" does this then mean our measurements are more accurate vs measuring from a hose and does that also apply to power nozzles which have smaller openings before it.
If that doesn't apply to machines which have smaller openings before the nozzles wouldn't this then mean that the airflow of a direct air would be substantially higher than non direct air then.... but if it does apply then we would have a higher airflow number at the nozzle wouldn't we?
What Bill is telling us is we're measuring 100% of the air coming through the vane area. It's not quite like a duct where the opening is larger than the vane itself where we need to figure out the total air moving based upon a speed given to us by a gauge....we are seeing ALL of the air moving through that vane.
I suppose I could ask our HVAC guy about this sort of situation to see what his thoughts on it are.
I'm going to play Devil's advocate here and ask this question. When we place machines like Kirbys or Royals onto our airflow boxes and the opening from said airflow box is 2" does this then mean our measurements are more accurate vs measuring from a hose and does that also apply to power nozzles which have smaller openings before it.
If that doesn't apply to machines which have smaller openings before the nozzles wouldn't this then mean that the airflow of a direct air would be substantially higher than non direct air then.... but if it does apply then we would have a higher airflow number at the nozzle wouldn't we?
What Bill is telling us is we're measuring 100% of the air coming through the vane area. It's not quite like a duct where the opening is larger than the vane itself where we need to figure out the total air moving based upon a speed given to us by a gauge....we are seeing ALL of the air moving through that vane.
I suppose I could ask our HVAC guy about this sort of situation to see what his thoughts on it are.
cheesewonton
Well-known member
That is a tough question I have often asked myself watching tests of uprights on Vacuum Wars. On something like a Kirby the suction inlet from the nozzle to the fan is a good two inches or more ( I haven't measured but it is much larger diameter than the hose ). On something like a Sebo, Panasonic, my Hoover Hushtone, etc, what you get is what is available at the end of the hose where it enters the nozzle base. On a Sebo G4 or similar, pull the hose out of the wand and measure the airspeed and multiply that by the area of the hose opening. It would be analogous to measuring the airspeed at the bottom of the wand on a canister vac and multiplying it by the area of the wand opening. That is all you get at the nozzle end.
I am going to go back to your post with the airflows you claim for that Tristar CXL and calculate the airspeeds you measured. Simple algebra. Take the airflow in CFM, divide by the area of a 2 1/2 inch diameter hole and that is your airspeed in ft/mim. I want to take those airspeed numbers and multiply them by the actual diameter of the hose opening and hose end, which I have already calculated based on a measured 28 mm ( 1.1 inch ) orifice to see what kind of airflow numbers that calculation produces. Give me a few minutes to go back in this thread three pages ( ! ) and find the values to use.
cheesewonton
Well-known member
So here is the math head in me. I will use Blackheart's numbers for the Tristar CXL and divide his CFM numbers by 0.026099 to arrive at the airspeed values he measured. Then I will multiply these by the area of the hose opening for each vacuum based on a 1.1 inch diameter opening for the Tristar.
For the CXL Blackheart shows 132 cfm at the canister opening and 104 cfm at the hose end. If you divide these cfm values by 0.026099 you get an airspeed of 5057.665 ft per min at the canister opening and 3984.827 ft per min at the hose end. If you multiply these by the area of a 1.1 inch diameter opening, or 0.0066 square feet you arrive at 33.38 cfm at the canister opening and 26.30 cfm at the hose end. Huge difference.
My own numbers were based on the smallest duct area setting on my anemometer, 0.01 square feet. As I mentioned earlier using that setting means I am overestimating airflow for hoses with openings smaller than 35 mm since a 35 mm opening is closest to 0.01 square feet ( 0.0104 sq ft to be exact ). So for giggles lets take the 52 cfm number I get on my anemometer for my DXL ( and my EX-30, and my EXL, etc, Tristars are boring that way ) and divided it by 0.01 to find the airspeed my anemometer measured, or 5200 ft per minute airspeed, higher than what Blackheart's anemometer measured. Take that 5200 ft/min and mulitply it by the area of a 1.1 inch diameter hose opening ( measured inside diameter of the Tristar hoses I have ) and you get 34.32 cfm. Now you see that Blackheart and I are not so far off, and our numbers are well within the parameters of the publish performance for the motors you find in a CXL. It passes the reasonableness test. Also want to mention that an Ametek 115923 is rated for 96 cfm at a 1.125 inch orifice with no other obstructions. Pretty interesting to see how much the design of the vacuum degrades performance from the motor face to the hose opening.
For the CXL Blackheart shows 132 cfm at the canister opening and 104 cfm at the hose end. If you divide these cfm values by 0.026099 you get an airspeed of 5057.665 ft per min at the canister opening and 3984.827 ft per min at the hose end. If you multiply these by the area of a 1.1 inch diameter opening, or 0.0066 square feet you arrive at 33.38 cfm at the canister opening and 26.30 cfm at the hose end. Huge difference.
My own numbers were based on the smallest duct area setting on my anemometer, 0.01 square feet. As I mentioned earlier using that setting means I am overestimating airflow for hoses with openings smaller than 35 mm since a 35 mm opening is closest to 0.01 square feet ( 0.0104 sq ft to be exact ). So for giggles lets take the 52 cfm number I get on my anemometer for my DXL ( and my EX-30, and my EXL, etc, Tristars are boring that way ) and divided it by 0.01 to find the airspeed my anemometer measured, or 5200 ft per minute airspeed, higher than what Blackheart's anemometer measured. Take that 5200 ft/min and mulitply it by the area of a 1.1 inch diameter hose opening ( measured inside diameter of the Tristar hoses I have ) and you get 34.32 cfm. Now you see that Blackheart and I are not so far off, and our numbers are well within the parameters of the publish performance for the motors you find in a CXL. It passes the reasonableness test. Also want to mention that an Ametek 115923 is rated for 96 cfm at a 1.125 inch orifice with no other obstructions. Pretty interesting to see how much the design of the vacuum degrades performance from the motor face to the hose opening.
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