Measuring CFM?

[cheesewonton]

Ideally I would move the anemometer probe around the circumference of the hose opening to see what the velocity reading is and take a reading at the center and average these but the length of the wire in the probe is nearly the diameter of many typical vacuum hoses so the best one can do is take a reading from the center. But I can see where I might get a high velocity reading from a given vacuum where someone using a vane anemometer 2 1/2 inches diameter with a hood would get an artificially low velocity reading. With hose openings as small as 28 mm I don't have a good work around unless there is an anemometer with a smaller sensor.

Japan has a method of rating vacuum performance they call Suction Work Rate that involves measuring total volume of air moved over a period of time. They don't use an instantaneous measurement of air velocity or airflow but instead measure volume in cubic meters over a period of time and this is accomplished at the end of the hose. They multiply this by, as best I can tell from the translation, a measurement of sealed suction at the hose end in Pascals and then by a factor to arrive at a value they express in watts. Some of the best Japanese bagged canister vacuums have pretty spectacular Suction Work Rate ratings.

 

[cheesewonton]

Sorry for my late reply. As I am not so familiar with these questions, I asked our expert Mr. Narisawa. Please see below his answer.

All the best for you!

Anton

From: n.narisawa <[email protected]>
Sent: Thursday, September 16, 2021 10:19 PM
To: 'Anton Jatsch' <[email protected]>
Cc: 厚木　奥津さん <[email protected]>
Subject: RE: Suction Work Rate

Dear Jatsch-san

The suction power is a unit (W) that expresses the suction strength of a vacuum cleaner unique to Japan. Thirty years ago, it was between 150W and 400W, but as consumers began to choose a vacuum cleaner with a strong suction, it became a meaningless competition for strength. It has a 680W home vacuum cleaner like no other in the world.

Calculation method of suction power

The method of measuring the suction power is defined by the standard "JEM 1454" set by the Japan Electrical Manufacturers' Association standard. The method is to attach the attached hose and extension pipe straight to the vacuum cleaner body with a new dust collection bag or filter, attach a measuring device to the tip of the extension pipe, and operate the air volume (per minute). The volume of the wind. The unit is cubic m / min) and the degree of vacuum (unit is Pa) is measured. Then, the suction power is calculated by multiplying the measured air volume and the degree of vacuum by the specified coefficient.

The formula is as shown below.

・ Suction work rate = 0.01666 x air volume (cubic m / min) x vacuum degree (Pa)

The suction power is the value required under the method specified in the standard. There is no doubt that the higher the number, the better the suction power.

However, as introduced earlier, when calculating the suction power, it is measured with only the hose and extension pipe attached. Also, at the time of measurement, it is not actually measuring while sucking dust, it is just sucking air. The value is calculated in a situation where the tip nozzle is not attached and the dust collection bag and filter are not clogged at all, so it is far from the actual usage situation.

In other words, the suction power is a value that measures only the suction force, not a value that directly indicates the ability when actually cleaning with the vacuum cleaner. For example, even with the same vacuum cleaner, the ability to suck in dust changes significantly between using a nozzle equipped with a power brush (a brush mounted on the head and rotating by a motor) and using a nozzle without a brush. increase.

The ability to suck in dust changes due to various factors. However, the suction power does not take that into consideration at all. This is the biggest drawback of suction power.


Kind regards,

Narisawa

 

[cheesewonton]

Now you know why all those old Japanese made Panasonic vacuums were called "Jet Flo 180" or Jet Flo 240". The numbers represented their Suction Work Rate.

Btw, I have one of those 680 watt ( Suction Work Rate ) vacuums from Hitachi and the power has to be experienced to be believed. One of my daily drivers is a 650 watt Hitachi CV-KP300J. These are available occasionally in the US through Amazon and even sometimes on eBay. I bought mine through a Japanese proxy buying service called Buyee. Great service!

For comparison sake using the Japanese rating system Tristars new and old sold in Japan manage 190 watts. My Vorwerk Tiger 260, sold in Japan as the Lux Sora, is likewise rated at 190 watts. Most Lux International vacuums sold in Japan earn 220-240 watt ratings. Modern Mieles sold in Japan earn the same. But in Japan even a low powered bagless vacuum has 300 watts and up and current production Panasonic bagged canister vacuums like the MC-PJ24G boast 580 watts. Then you have these over the top Hitachi vacuums that are teeny-tiny things with unbelievable power.

 

[Vacuum Facts]

So far, my involvement has just been to explain how the amateur measurements championed are not representative, and seemingly unknowingly, often in contrast to unsupported grandiose claims of capability. Solutions are possible but require a number of physical measurements. The Japanese standard (one of many, globally), referenced in the email, describes other methods, but they’re not really within the remit of amateur bedroom testers. Some of the statements in that email aren’t quite correct and can’t just be attributed to translation—won’t go into that here though, but it just goes to show that just because someone claims they’re an ‘expert’ or works for a vacuum cleaner manufacturer, doesn’t mean they are…

If I’d have spent more time developing that video before posting, I’d have proposed more methods which could be used to measure flow rate. You could, for example, machine a very precise orifice plate in a duct and measure the pressure drop across it and then use the Bernoulli equation and discharge coefficient across it to determine flow rate using Q=C_d . A. sqrt((2 deltaP)/Rho). I suspect this is a bit too complicated for many bedroom testers who would need skills in professional experimentalism (not least to accurately calibrate), basic circuit theory, fluid dynamics, and the ability to manufacture precise parts.

You could also measure the mass flow, if you had a mass flow controller (very expensive) and do the appropriate maths to determine flow rate. There’s also the method you used, which is to attempt to determine the radial velocity profile using your hotwire probe and apply a correction factor, but this is tricky at small physical scales, time consuming, and still rich with sources of error.

The easiest method that I’m surprised none of the alleged ‘experts’ commenting have thought of, or even the ‘experts’ from Vorwerk, since it’s obvious, is to use a simple sealed-bag displacement method, which measures how fast a known volume of air is displaced by the vacuum cleaner. Perhaps it’s the complete failure to understand what airflow is, even dimensionally, from what I’ve read in this very thread, that prevented such a simple test from being recognised. You start with a deformable bag of known volume, turn on the vacuum cleaner, and time how long it takes to suck that air out until the bag collapses fully (or partially). The rate of change of volume (V/t) is your volumetric flow rate.

I’m half tempted to remake that video and demonstrate this method with my bag, since I have one, and compare the numbers you get with those from a vane anemometer. Worth me doing (even though measuring airflow is literally irrelevant)? I do have a spare evening tonight, unusually.

 

[Vacuum Facts]

Based on feedback on my original video version and your comments, I've updated the video as discussed above. It now contains a demonstration of a simple and direct way to measure airflow. This is compared against a vane anemometer under the same conditions. In short, vane anemometers can overestimate the airflow measured through a hose or 'airflow box' because they assume a flow structure not always provided. Also worth remembering that measurements of airflow as often shown have no direct relevance to cleaning performance at all, as outlined in my lecture of the associated well-understood science, which I will also link below for convenience (click to watch on YT).

Updated airflow measurement science video:


Lecture covering the science of how vacuum cleaners really work:

 

[cheesewonton]

If, as you claim, airflow is not important for cleaning then explain why the normal measure of a vacuum's cleaning power, Airwatts, is the product of suction expressed in Pascals and airflow expressed in cubic meters per second? Looking at any vacuum motor performance chart you always see maximum air watts occurs where the lines for suction and airflow for a given orifice diameter intersect. It seems to me both airflow and suction are required and the more of both the better. Too much of one and not enough of the other doesn't get your home cleaned. Suction alone won't clean your home, even with good agitation.

In the fullness of time my plan is to build a device that allows me to measure airflow and suction simultaneously at the hose end. Not sealed suction but the suction measurable from an open hose end. Assuming the measurements are accurate ( not so easy ) one could calculate the airwatts being generated at the end of the hose. That would be more informative than sealed suction and raw airflow.

Also want to mention that the way the vane anemometer was used, the vane anemometer underestimates airspeed, not overestimates it. The overestimate of airflow is the result of using the diameter of the van rather than the diameter of the hose for the surface area of the orifice used to calculate airflow. You can see that the vane anemometer underestimates airspeed from my calculations of airspeed for Blackheart's Tristar. I took his claimed airflow numbers, divided these by the surface area factor he used and came up with airpseeds for each airflow value. For the Tristar his airspeeds are lower than those I measured using a thermal probe anemometer. This was compounded by using that duct because as the diameter of the duct opens airspeed will decline from the hose opening to the anemometer vanes.

 

[Vacuum Facts]

If, as you claim, airflow is not important for cleaning then explain why the normal measure of a vacuum's cleaning power, Airwatts, is the product of suction expressed in Pascals and airflow expressed in cubic meters per second? Looking at any vacuum motor performance chart you always see maximum air watts occurs where the lines for suction and airflow for a given orifice diameter intersect. It seems to me both airflow and suction are required and the more of both the better. Too much of one and not enough of the other doesn't get your home cleaned. Suction alone won't clean your home, even with good agitation.

In the fullness of time my plan is to build a device that allows me to measure airflow and suction simultaneously at the hose end. Not sealed suction but the suction measurable from an open hose end. Assuming the measurements are accurate ( not so easy ) one could calculate the airwatts being generated at the end of the hose. That would be more informative than sealed suction and raw airflow.

Also want to mention that the way the vane anemometer was used, the vane anemometer underestimates airspeed, not overestimates it. The overestimate of airflow is the result of using the diameter of the van rather than the diameter of the hose for the surface area of the orifice used to calculate airflow. You can see that the vane anemometer underestimates airspeed from my calculations of airspeed for Blackheart's Tristar. I took his claimed airflow numbers, divided these by the surface area factor he used and came up with airpseeds for each airflow value. For the Tristar his airspeeds are lower than those I measured using a thermal probe anemometer. This was compounded by using that duct because as the diameter of the duct opens airspeed will decline from the hose opening to the anemometer vanes.

Hi. I've given full treatment to what you ask in the lecture linked to in the previous comment, which fully explains the very question you ask, including a detailed explanation from first principles of the relationship between suction, air watts, and airflow.

As for your future box, the suction at the open hose is only relevant for above floor cleaning. There will be a huge drop due to the high leakage current and greater air power will be required to sustain it and the airspeed (which is what's important for cleaning). Again, you'd do well to learn the science from the lecture. It's all there for you.

There are a few mechanisms that cause minor underestimation of airflow, but the net result in this kind of system is overestimate. This is shown from the discussion of the well-understood fluid dynamics and also empirically in the above video. The method you used (area normalisation) is likely flawed for the reasons discussed in detail in the video, although without seeing sufficient detail of the experimental setup of the source you reference, it's hard to comment further on that data or be completely confident.

 

[huskyvacs]

I vote to bring back asylums to get rid of these narcissists that exist only to endlessly yap and try and 1UP each other's egos with minsinformation. Convinced its all one person parroting themselves across multiple accounts. All have the same manner of speaking - like an NPC.

 

[centralvacguru]

Sorry I haven't posted for ages on this forum but I just have to chime in here a bit to add a few other ideas, not to argue for either side. Someone in the above string said it right that CFM and waterlift work in direct opposite of each other. And it is all dependent upon the opening size. At a “Zero” opening you have “0” CFM and the highest waterlift. As the opening gets larger, the CFM increases and the waterlift decreases. In the central vacuum world the manufacturers post specs for waterlift at the 0” opening and CFM at a 2” opening which is the maximum for each. Typically motors with more stages will produce higher waterlift and lower CFM for the same amperage of power usage.

I have used various “Baird” type meters and actually blew the fans out because it spun too fast on one of my units. But have never seen an accurate translation of their information into CFM. Most manufacturers simply post the specs provided by their motor manufacturers and this does not correlate to real life at the end of the nozzle. (See Vacuumland post by Wyaple on 5/2/2016 https://vacuumland.org/threads/baird-meter-hose-cfm.31859/ )

For our company, we produce power units that have two 3-stage motors in air-parallel (both sucking on the same tank at the same time) and we get in excess of 200 CFM but almost 140” Waterlift. We can take the same motors and run them in air-series (one sucking off the exhaust of the other) and get 100 CFM and 240” Waterlift. But these measurements are derived from box tests run by the motor manufacturer.

Back in the 1990’s ASTM came up with a measurement that combined both CFM and Waterlift by measuring the CFM and Waterlift at all the openings from 0” to 2” and drawing a curve. They then would express the “Maximum Air Watts” where the curve peaked, typically at about ¾” to 1.25” in opening. https://store.astm.org/f0558-24.html. While this is not a perfect measurement, it has given some truth to the idea that a higher number would mean better cleaning power. But it still does not answer KirbyNphone’s original question, I don’t know of any effective accurate meter that is commercially available that would provide CFM in a tangible way that we can use in the vacuum sales industry. If you guys find one, I would be very interested!!!

 

[Vacuum Facts]

Then at the risk of narcissism, yapping, and trying to 1-up ego with ‘misinformation’, aka helping those that might be interested to understand well-established and fact-checkable science on a public discussion forum intended for exactly that, I’ll elaborate why the anemometer overreads airflow through a duct or airflow box. (Edit: Someone explicitly asked me for this BTW, so I thought it was worth posting here.) For a fixed airflow, the speed of the turbine in laminar flow is lower than it would be for non-uniform flow with a radial velocity profile that is relatively lower at the edge and relatively higher in the bulk centre. This radial profile is set up because of the pressure profile that forms downstream for various fluid dynamic reasons. The higher airspeed in the centre bulk region dominates the force applied to the turbine and drives it relatively faster (see my lecture for the equation describing this drag force and its dominant relationship with air velocity). If you plot the power law function approximation that typically describes the flow profile in ducts to first order (see attached image), you can visualise the radial velocity profile to appreciate why the air turbine is driven by the bulk centre velocity (I took it out of the video at the last minute and regret that now). The precise radial functional form and ‘peakedness’ of the centre velocity stream will depend on individual setup and a myriad of other factors and would need sophisticated modelling to determine it precisely to know a more accurate correction factor. The anemometer therefore detects a higher airspeed that isn’t actually present at the edges, but it internally calculates as though it is by virtue of assuming a laminar flow. Since it calculates airflow based on airspeed, it thus overreads it by roughly the amount calculated in the video (and empirically supported to some degree in my quick test—but it’s well-established in the scientific literature from empirical studies, regardless). Upshot: using vane anemometers to measure through enclosed spaces (non-laminar flow) will give overestimates of airflow and there are better methods that rely on timing extraction of known volumes, as demonstrated in my video. (…Also, measuring large airflows that occur in the presence of very low air resistance, such an an open hose, is irrelevant to vacuum cleaner performance when sealed to flooring when air resistance is much higher…see lecture.)

 

[panasonicvac]

Sorry I haven't posted for ages on this forum but I just have to chime in here a bit to add a few other ideas, not to argue for either side. Someone in the above string said it right that CFM and waterlift work in direct opposite of each other. And it is all dependent upon the opening size. At a “Zero” opening you have “0” CFM and the highest waterlift. As the opening gets larger, the CFM increases and the waterlift decreases. In the central vacuum world the manufacturers post specs for waterlift at the 0” opening and CFM at a 2” opening which is the maximum for each. Typically motors with more stages will produce higher waterlift and lower CFM for the same amperage of power usage.

I have used various “Baird” type meters and actually blew the fans out because it spun too fast on one of my units. But have never seen an accurate translation of their information into CFM. Most manufacturers simply post the specs provided by their motor manufacturers and this does not correlate to real life at the end of the nozzle. (See Vacuumland post by Wyaple on 5/2/2016 https://vacuumland.org/threads/baird-meter-hose-cfm.31859/ )

For our company, we produce power units that have two 3-stage motors in air-parallel (both sucking on the same tank at the same time) and we get in excess of 200 CFM but almost 140” Waterlift. We can take the same motors and run them in air-series (one sucking off the exhaust of the other) and get 100 CFM and 240” Waterlift. But these measurements are derived from box tests run by the motor manufacturer.

Back in the 1990’s ASTM came up with a measurement that combined both CFM and Waterlift by measuring the CFM and Waterlift at all the openings from 0” to 2” and drawing a curve. They then would express the “Maximum Air Watts” where the curve peaked, typically at about ¾” to 1.25” in opening. https://store.astm.org/f0558-24.html. While this is not a perfect measurement, it has given some truth to the idea that a higher number would mean better cleaning power. But it still does not answer KirbyNphone’s original question, I don’t know of any effective accurate meter that is commercially available that would provide CFM in a tangible way that we can use in the vacuum sales industry. If you guys find one, I would be very interested!!!

Welcome back and thank you for making MD central vac units. I had one of the SilentMaster models before, other than not adding any inlets on the third floor up and out in the shed, it was the perfect vacuum for the cabin.

You're exactly on point. At least that's what makes more sense to me.

This will be my last post and view on this thread because the whole argument with some other users here just made it less enjoyable to continue reading on but I do have this to say. Other than my other post showing the suction meter from one vacuum shop, this other dealer confirmed that airflow matters more than suction (the penny test had me convinced). They did had a couple more videos of the Royal Everlast 8300 compared to the Dyson DC28 and red Riccar Radiance but I think they got taken down by Tacony's request because it made the Riccar look bad by the Royal having more airflow (technically it's true) which I totally understand.

 

[cheesewonton]

After pondering this for a while it dawned on me I kind of knew about the error in using the center line velocity measurement for a long time but it didn't dawn on me to correct for it. I know from fooling around with engines that intake manifolds and intake ports in the cylinder head have a "boundary layer" of dead air along the cylinder walls that effectively decreases the diameter of the port.. Dead air isn't moving. One can mostly eliminate the boundary layer by scuffing the walls of the intake manifold(s) and intake ports in the direction of flow, effectively increasing the manifold and port size and thus increasing airflow to the engine. There are other things you do like knife edging the valve guide bosses or even eliminating them ( sacrificing some durability for speed in racing engines ).

I even fooled around with this on the hose of a Sanitaire SP6952 that has huge airflow at the hose opening but hardly anything at the hose end. I cleaned up the insides of both hose ends, removed molding flash, rounded the sharp corners and scuffed the walls in the direction of flow. I doubled airflow at the hose end measured with a BAIRD Meter ( didn't have the jingle yet for a real anemometer ) from 1.5 to 3. Still pretty weak when it pulled 9.0 at the canister opening but progress.

So I did some reading along with squinting hard at what Vacuum Facts wrote and found a factor that one can use based on the diameter of the cylindrical tube air is moving through. It's based on something called a Reynolds Number ( which is different for every fluid, and air is technically a fluid ) to estimate the average velocity of the air based on the unrestricted centerline velocity, which is all I can reasonably measure using an anemometer in a duct as small as a vacuum hose. Without going through all the math an approximation used for the average airspeed of turbulent air moving through a cylindrical duct is roughly 0.8 times the unrestricted center line velocity you measure with your anemometer.

Interesting discussion. Learned a lot from it.

 

[Vacuum Facts]

Sorry I haven't posted for ages on this forum but I just have to chime in here a bit to add a few other ideas, not to argue for either side. ...

This is a really interesting post and I’m able to shed further light in case you’re interested:

>> “At a “Zero” opening you have “0” CFM and the highest waterlift. As the opening gets larger, the CFM increases and the waterlift decreases.”
This behaviour describes the relationship between suction and air current for a given air power. The air power is the product of the two; the same power is achieved with an interchange of one with the other depending on the resistance level (detail here youtu.be/_CzzDiArrrg)

>> “I have used various “Baird” type meters and actually blew the fans out because it spun too fast on one of my units…Most manufacturers simply post the specs provided by their motor manufacturers and this does not correlate to real life at the end of the nozzle.”
When installed into a central vac system, the lengthy ducting produces substantial resistance to air, leading to pressure losses. This is often why the motors have to be powerful—to compensate for the increased resistive load. So, when that’s removed by a shortened circuit flow measurement, almost all of the motor’s maximum power can be realised, leading to both high suction and air current, and blowing your fan out (maximum power transfer theorem).

>> “we produce power units that have two 3-stage motors in air-parallel (both sucking on the same tank at the same time) and we get in excess of 200 CFM but almost 140” Waterlift. We can take the same motors and run them in air-series (one sucking off the exhaust of the other) and get 100 CFM and 240” Waterlift.”
Parallel circuits are often configured to give large currents; series for large suction (analogous to voltage in electrical circuit theory). Both deliver the same power, but you’d choose the parallel setup if you had a use case where there was substantially large currents of air being drawn in during use with low air resistance (open hose use). This way you can sustain suction and air speed. The series case is more useful if you need to utilise that same power to give much stronger suction, e.g. in high resistance setups that don’t have large leakage air currents (sealed carpet cleaning).

>> “Back in the 1990’s ASTM came up with a measurement that combined both CFM and Waterlift by measuring the CFM and Waterlift at all the openings from 0” to 2” and drawing a curve. They then would express the “Maximum Air Watts” where the curve peaked, typically at about ¾” to 1.25” in opening.”
If you’re interested in where this observation comes from, you have to go to vacuum dynamics (or basic electrical circuit theory). Please see attached equations. While air power (air Watts) are a product of suction and airflow, airflow is also a function of air resistance, and so power scales with the square of suction. However, the suction is also a function of air resistance, meaning the expression for air power is non-linear and reaches a maximum at a specific value of air resistance (or opening size), and why the ‘air Watts’ curve peaks. I’ve also attached a plot showing the functional forms of airflow, suction, and resulting air power from the equations. The red peak is why you see the ‘maximum air Watts’ at a given opening size.

>> “While this is not a perfect measurement, it has given some truth to the idea that a higher number would mean better cleaning power.”
This is correct (partially). In general, more air power means more suction in high resistance situations (like a head sealed to a carpet) and less suction loss in low resistance situations with lots of leakage current (e.g. above floor cleaning). Maintaining suction is important because it determines airspeed, which is the dominant parameter that accelerates particles in a fluid flow (see this lecture for the more detailed science youtu.be/_CzzDiArrrg). The design of the cleaner head, the properties of the dirt particle, and the nature of the carpet are also important considerations. While more power is usually better, it’s also more energetically expensive of course, and so better designs of cleaner head allow the same or better levels of dirt extraction from a given carpet type without needing to use as much energy.

>> “I don’t know of any effective accurate meter that is commercially available that would provide CFM in a tangible way that we can use in the vacuum sales industry. If you guys find one, I would be very interested!!!”
You’d have to set up a professional experiment to measure various properties, such as mass flow, pressure drops, or time known volume extraction (see video youtu.be/GkcCBVmIpJI).

 

[Vacuum Facts]

...

Incidentally, that penny test demo needs to be understood carefully. The reason the penny didn’t move is because he blocked the hose completely thereby increasing the resistance to infinity, which made the air speed zero and therefore imparts no force on the penny. The air (and not necessarily a lot) has to move to impart force. Within a cleaner head sealed on carpet, there is always air moving. It’s much less than with an open hose people always measure and is the topic of this thread, but there’s always some fluid flow. The cleaner head increases the speed of the relatively lower airflow via the Venturi effect to increase cleaning performance. Notice how the penny only moved when he brought the nozzle close to his hand where the air speed is greater (the airflow was still the same before he got close but it didn't move). This is why he enclosed the penny in his hand BEFORE even turning the machine on and off, so it prevents air from moving at all, which is very sneaky if you don't know to spot the tricks of the trade. The importance of air speed is discussed in detail in this lecture.

Another thing about that first video was his claim that dirt far away from the hose under the head causes it to not be picked up. This isn’t true. He misinterpreted what he saw. The edge with the narrow gap edge-cleaned best. The edge with the belt wasn’t cleaned as well because the belt guard prevented it. If what he’d said was true, the front edge pickup he showed would have had a clear gradient, with less dirt nearer the hose end. Instead, it was completely unform all across it, completely disproving what he was saying. Ironically his direct airflow machine demo worked better because it was producing more suction than the previous model. The toilet tube and sand in the rug demos are debunked at the end of the lecture above for anyone interested in learning the tricks of the trade.

 

[Vacuum Facts]

So I did some reading along with squinting hard at what Vacuum Facts wrote and found a factor that one can use based on the diameter of the cylindrical tube air is moving through. It's based on something called a Reynolds Number ( which is different for every fluid, and air is technically a fluid ) to estimate the average velocity of the air based on the unrestricted centerline velocity, which is all I can reasonably measure using an anemometer in a duct as small as a vacuum hose. Without going through all the math an approximation used for the average airspeed of turbulent air moving through a cylindrical duct is roughly 0.8 times the unrestricted center line velocity you measure with your anemometer.

Interesting discussion. Learned a lot from it.

That number is about right; glad you came to the same conclusion. The full derivation of this value from first principles was in my video for anyone interested in seeing the maths. The precise value does vary based on the Reynolds number (indirectly) and many other fluid dynamics factors which need to be considered if identifying a correction factor precisely for a given setup (only briefly mentioned in the video). Again, for anyone who wants to learn more, this lecture meticulously works through the relevant science. Thanks for the enjoyable conversation!

 

[rivstg1]

In terms of CFM

you cannot be a direct air machine i have a baird meter the kirby G6 measures in at a 10 at the fan a 7 at the end of a hose

The most powerful canister i've measured was the Kenmore Magic Blue which also pulled a 10/10 i was shocked

I've measured some of the vacs i have if you are interested here's what i have recorded
Vita vac (airway) with the Airtech cloth bags pulls a 6 with paper 4
Dirt Devil Deluxe 3/10
Dyson DC-11 2/10
Dyson DC-17 1.5/10
Electrolux olympia 4.5/10
Hoover Celebrity II Elite 3/10
Hoover Windtunnel Plus 8/10
Lindhaus Aria Platinum (measured at a vac store 6.5/10
Miele Silver Moon 5/10
Patriot 5.5/10
Riccar 1700 5.5/10
Royal Classic Power Tank 2.5/10
Simplicity 7 series 7.5/10
Silver King Blue max 3
Thermax AF1 .5
Tristar CXL 5
Tristar CXL 5

I know i have measured others but i cannot recall their numbers

wow the Patriot ONLY pulled a 5.5? I'm amazed and disappointed a bit

 

[blackheart]

wow the Patriot ONLY pulled a 5.5? I'm amazed and disappointed a bit

Being so long ago and having no documentation of the condition of the machine it's hard to say why it pulled those numbers. It should have pulled closer to a 7/7.5 really. I'd imagine the post motor hepa filter is probably partially responsible, or maybe the cloth bag was dirtier than thought.

 

[cheesewonton]

wow the Patriot ONLY pulled a 5.5? I'm amazed and disappointed a bit

I'm weird for Tristars and their many derivatives. I have a Compact Model 1, C2, C4, CXL, DXL, EX-30 ( from Japan with Sunstorm branding - oh my ), an MG I converted to an EXL with an uprated motor from Electromotor LLC, a stock MG and another into which I finagled the Panasonic 3D Inducer Motor from a Kenmore Elite ( 600 air watt motor ). I also have an Airstorm, a Patriot P1, Miracle Mate Mk-1 and Platinum, a Haley's Comet and a Vortech XR-3000. One of the things I have noticed about Tristars is that it seems no matter what motor you put in them the only produce about 28 cfm at the hose end. The hoses are actually only 1.1 inch ( 28 mm ) inside diameter measured with my calipers and that includes the newer ones with Aerus style hose handles. Tristar exhaust ports are just as tiny. You literally cannot push more air through them even with a more powerful motor. The best I have managed from any Tristar is 30 cfm from the one with the Panasonic motor ( same motor produces 44-45 cfm in a Kenmore Elite with its 40 mm diameter hose opening ). Patriots are only marginally better. With a Stormy open top paper bag and the big Medick Aire filter my P1 produces 30 cfm. Removing the Medick Aire filter gets you 31-32 cfm. That filter is not very restrictive. If you swap the Stormy bag for the thicker closed top Hybrid bag still using the Medick Aire filter you are down to a pinche 28 cfm. Miracle Mate and Vortech have larger exhaust filter areas and not surprisingly move more air. The Miracle Mate Platinum moves about 34-35 cfm and the Vortech XR-3000, which has a larger diameter hose and normal square pleated exhaust HEPA filter manages 49-50 cfm. Best of the breed but rare and weird as all heck.

What really surprises me is my Kenmore 600 Series 81614, the Purple People Eater, produces 72 cfm at the hose end, resoundingly spanking the Elite.

 

[kenc184]

I was left thinking that Cheesewonton was right, and that the hose diameter must be a factor. But then Vac lab showed his cone adapter, and stated cfm in = cfm out. And that seems hard to argue with. Seems like if the vane has (say) twice the area of the hose, then the airflow of both must still be the same if it's a closed system. The air velocity will certainly go up as the cone reduces, but the cfm must remain the same.
Seems like lower velocity x larger area of vane = higher velocity x lower area of hose.
So is the vane anemometer somewhat accurate to first order? Or am I full of it?

 

[blackheart]

It stands up logically. I spoke to our HVAC guy who, while he told me the calculation of CFM is something he's not super comfortable with, to think of it like a funnel and hose filled with water. The hose is going to be the point with the most resistance but when they're working in a system the flow rate will be the same but as you stated the speed changes based upon the area of the orifice.
He also said it's not an exact calculation you're looking for a ballpark. Which when a most of us measure vacuum airflow we use the max setting to see the maximum speed of the air but if we leave that off we'll often see an amount of fluctuation.

I've said and thought for quite a while my measurements are a ballpark not an absolute. Environmental factors will have an effect on them, but i'll continue to keep doing them because i find it interesting to see how different designs and different factors effect the performance.
Just recently I tested a "12 amp" Eureka Bravo II and while I think many of us would just assume that it's performance would be close to an equivalent hoover elite I found that it wasn't having about 102 nozzle cfm and 20" Now all but one of the elite style machines, a hard body dimension, surpassed it's airflow even the 5.5 amp runabout did just slightly better at about 103 nozzle cfm, but only the 12 amp caddy vac matched the nozzle suction. Without measuring these things how could we have known that.
I don't know about the rest of you but I find it so interesting to have a meaningful way to measure and compare the specs against each other. In the past besides a few suction gauge readings which really only tell part of the story It seems like we just relied on people's intuition which.....can be iffy. Model X is more powerful than Model J etc etc.

I'm getting off topic here....I'd assume due to tiredness. We had a pretty major storm watch up here so i've been waiting it out.
The calculation for the area of a round duct in square feet if you're starting in inches is is πr²/144
If we take that and multiply that cross section by the airpseed measured in Feet per Minute we get CFM.
I just threw this together as an example of how the area of the tube makes a different there's a massive different in the air speed to move the same volume of air but even if they were connected together and you got 100 cfm in you'd get 100 cfm out.