«You learn something (new) everyday unless you are really careful»
-- Tom Van Vleck, Multician
«Before you say something, ask yourself, "is it True?", "is it Helpful?" and "is it Kind?" and then don't say anything unless at least 2 of the 3 answers are true.»
Here's a fun tidbit: those $10 20-inch Lasko Box Fans supposedly circulate 2,500 CFM. Very low suction/pressure though, if you put it too close to a wall, it will move much *less* air. A typical forced-air furnace also moves about 2,000 CFM for a regular home and can overcome more significant "friction" because it uses a more powerful motor and it's able to generate more suction/pressure to overcome the resistance to air movement.
For vacuum cleaners specifically, pure "inches of water lift" are measured at or close to zero cubic feet/minute, which is why it's also known in the field (Transport Phenomena / Fluid Mechanics / Aerodynamics) as "sealed suction/pressure". It's only *one* datum on a (usually) curve, and the charts/graphs representing the universe of responses to that fan have way more than just one curve.
Same thing for airflow -- change the resistance even slightly, completely different airflow *and* pressure.
What people should be talking about is power, which in the case of vacuum cleaners is measured in Air Watts and, just like "horsepower", "amps", "watts", "inches of water-lift", "airflow" etc, it's another metric that can be misused and doesn't tell you much, although it's still a better metric than the previous ones, because it approximates better what people are trying to say/measure.
Remember, until a few years ago in Europe, people trying to do their housework were going to the store and picking up vacuums with the most "watts", which, in their case, was just how much the machine was *consuming* and they were paying the electric company for, but, as soon as the laws changed and limited the amount of raw power the machines could consume, a lot of manufacturers went back to the drawing board and came out with better fans that generated better airflow/suction and were better than the previous machines.
And even then, that's not always the answer either. Again, I hate to keep hitting on the same key(s), but how many times did a Hoover Convertible won contests and magazine/reviews tests? How powerful was the motor on those? How many airwatts did it develop? I seem to recall they did not develop as much airflow or suction as the Sanitaire or the Royal used in the video below.
Please keep in mind, the Dyson V8 used in the video supposedly develops up to 115 AirWatts in MAX mode (and can then run for about 6 minutes), but it can run for about 20-25 minutes in regular mode with the motorhead and develops only about 22 AirWatts then (which is what I was using and anyone that knows the machines can tell by just the sound -- I forgot to show the setting while filming, sorry). I am going to chance saying here that 22 AirWatts is *way* less than the Sanitaire or Royal develop. The Royal uses 10A and develops 1,200W which it shares with the fan *and* the brush, and I'm willing to bet the brush uses way more than 50W of power, which is exactly how much power the motorhead in the Dyson V8 uses, according to wikipedia.
It may be hard to notice in the video, but the Dyson V8 sucked up *plenty* of baking soda from the carpet, and that baking soda wasn't even brushed deep into the carpet, I just sprinkled it on top of it.
I would have preferred to have had more time to install new bags on the machines and *film* it be changed, so people wouldn't have anything to complain about, but my Director of Photography (aka my husband) wasn't in the mood to hold the phone for much longer than the 3-4 minutes in the video. I also regret that I didn't have a good enough tape to mark the area, but whatevs, it's better than nothing.
In advance of people choosing to bitch about stuff here, I will warn you that this is not the first time I run these tests. People who thought *they* could do better have in fact set the machines much closer to the carpet in an effort to make it brush more, and much higher than appropriate for the carpet in an effort to speed up the brush RPMs and *everything* in between, including what I attempted to do (set to the correct height), but there's something wonky in that the appropriate settings in my home vary, probably something to do with how well (or poorly) they installed the carpet -- it doesn't *feel* or *look* wrong, and the machines that have floating heads seem to take it in stride, but every once in a while one needs to reset the carpet height adjustment on the machines and I keep forgetting where that happens, sorry.
In any case, people who come to my home and see me run the tests or run the tests themselves will tell you it happens *exactly* like in the video and it happens even when you clean a whole area with what they think is the correct setting.
In any case, this is not the first time I end up in conversations like this one, I understand why: people want simple metrics to so as not to complicate things. And fluid dynamics is not an easy subject and it has many counterintuitive situations, just like this one. Before I started using the Dyson V8 to demonstrate this, I was using any vacuum with a suction-only carpet nozzle, and it could still pick up stuff. The last time few times I did this, we used a Dyson DC23 with a Flatout Head tool, which is not the tool with the least losses because it was designed to fit under very low furniture, and it still picked up stuff.
And I am tired of having this conversation and running the test(s) for people. Here, it's now on video. Complain all you want, but if you show up at my home and run the test yourselves, you will see exactly what I am showing in the video.
I'll be the first to admit that it's not exactly scientific, because a big part of the scientific method is being able to *reproduce* any tests at will by anyone who cares to follow the testing procedure, and in this case, I have no idea what carpet I have (and I suggest anyone to avoid buying the same thing if they can avoid it), but what I *can* tell you all is that we did this many many times, with flour, baking soda (as in this case), sand etc and the results even when not identical are in the same ballpark.
And, as one of my math professors was fond of saying, to prove a theory one needs to prove that it happens in all circumstances, but to _disprove_ a theory, all you need is one counterexample.
Here's my counterexample. Not a lot of airflow or a lot of suction or a lot of agitation. Still picks up stuff.
Thanks all for listening,
Enjoy!
;-)
