Thanks for you post, with tests!
Hutch,
Welcome to VL and thanks for posting some of your tests! It’s great to see someone else make objective measurements. Since you have quite a bit packed into your “wall-o-text”, I’d like to break it down somewhat.
“It appears in the post when you're talking about CFM and the dirty filters or bags have no bearing on it I don't believe that is quite correct.”
I’m not sure what you mean by being not correct. My tests were measuring CFM with no bags or filters. When most manufactures publish a specification for airflow (or maximum airflow), this is where they would start. Many canister makers don’t even take into consideration hose/power nozzle tube losses or even motor losses when the motor is placed in the machine body. Take Aerus for example, they claim their top-o-the-line machine has a motor which produces over 505 Airwatts. That can be very misleading because Airwatts is technically a point cherry picked from a graph. It doesn’t easily reveal CFM or water lift to the consumer. As my other posts here on VL have revealed, CFM loss is much less than what you would expect with cloth HEPA bags as the pores usually never clog all that much in regular (non-abusive) use.
“The first test that I do on vacuums is a test raw suction by putting a vacuum meter on it. Example Dyson DC41 will pull 28 kPa. Kirby Sentria will pull 14 kPa. Don't get upset with what I just said but keep in mind the Dyson does have double the amps of the Kirby so therefore it should be double the suction So Dyson's statement that the Dyson has twice the suction is correct however there's more to the equation.”
I know that outside of the U.S., many companies including Dyson post water lift in kPa, but that unit is much more easily understood if converted to inches of water (especially if graphing Airwatts). The conversion rate is 4 inches of water per 1 kPa.
Your DC41 = 28 kPa = 112”
Your Kirby Sentria = 14 kPa = 56”
Claiming a doubling of suction just because the motor draw is double the amps is a completely false statement. That would mean that all motors are essentially of the same performance “slope” and all one would have to do to decide how much power your machine would consume and would be to simply pick an engine off the shelf in the desired power category. Based on what the manufacturer wants, the very same total power usage results in widely varying CFM and water lift capabilities. Remember, motors may have more than one fan and this obviously greatly affect the CFM/water lift curves.
Incidentally, my measurements for my DC14 are 112” at the hose and 120” at the base with or without filters. CFM maxed out at 79 CFM at the hose (no filters) and 75 CFM (with filters). I still think it’s funny that Dyson keeps pushing the “never loses suction” mantra when it’s airflow that matters more. And their vacs definitely lose airflow, even the newer ones without any filters.
“I've done test to see which one actually picks up more dirt on the same pattern and path and every time the Kirby does a much better job. By the way I use a Dyson when I vacuum.”
I’m confused. You’ve seen that a Kirby does a much better job than a Dyson, but you still use a Dyson as your daily driver? While I have only a small collection of vacs and use them all (why have them if you don’t use them), I always make to sure use my Kirbys periodically if not more regularly to get all the dirt possible.
Rigid 6.5 HP shop vac:
Yes, the airflow of that shop vac is tremendous, it could filter the air in a room vary quickly at 300+ CFM!
Do you realize that those HP ratings are completely false? They are literally measured in the first few milliseconds of motor turn on. Steady state power usage of that machine is 12 Amps. 12 Amps at 120 Volts = 1440 Watts = 1.93 HP or about 2 HP. This is approximately the same current usage as the high power 12 Amp rated Dysons. So for the same power usage a Dyson produces 80 CFM-ish and the rigid produces over 300 CFM-ish. Of course, the motors are used differently, but I hope you see my point. Manufacturers pick a motor based on how they want the machine to perform, not just on a power usage slope.
Just for laughs, consider this:
Rigid @ 325 CFM using a real 12 Amps would mean an efficiency rating of 325/12=27.1 CFM per Amp at the hose, which betters just about everything out there I can think of, except maybe another shop-vac.
“And I also have to tell you I do agree 100% that for amps used the older Kirby's to include the newer Kirby's seem to perform far better then any of the newer Bagless vacuums.”
Bagless systems (and water based systems) are very inefficient by design unfortunately. Much of the motor’s CFM is lost by creating dirt tornados and jamming dirt into water. If you measure your Dyson DC41 at the motor base, you’ll find it may produce something like 120-130 CFM. My DC14 produced 128 CFM at the base (before all those 8 cyclones).
I look forward to reading more of your posts that include tests.
Bill
