Here Are Some Real World Figures
Since we never have "unlimited" current to prop up the voltage under an increasing load, the voltage will drop. Said another way, since we never have unlimited suction, the CFM will drop under an increasing load. Take a real long look at this actual motor performance chart.
At a 2" opening (low resistance), the CFM=141.5 and the suction=7.4"
At a 1" opening (medium resistance), the CFM=95.3 and the suction=56.9"
At a 0.5" opening (high resistance), the CFM=33.3 and the suction=112.7"
Same goes for current limited electrical circuits. When the resistance increases, the current increases to attempt to prop up the voltage as long as it can until it maxes out and then voltage drops.
You can witness a part of this behavior in countless videos I've made where I show the voltage drop under a 10A or 12A vacuum load (low resistance).
And don't forget that the absolute value of what CFM remains is always the key. If machine "X" loses 100 CFM and only has 50 CFM remaining, that is still quite better than a machine that loses 25 CFM and only has 25 CFM remaining.
So yes, I'm saying that a variety of dirty air machines, including Sanitaire, Royal, Kirby, classic Hoovers, etc., will have superior airflow on sealed carpets compared to low CFM bagless machines. They will not drop to something ridiculous like 10 CFM. Know how to tell? Because the vacuum would absolutely howl in protest and the motor would overheat in just a few minutes.
Have a listen to what happens when a Kirby dirt pad gets clogged and airflow drops. A properly height adjusted direct air machine won't sound like this. I just cleaned a 6000+ sq. ft. church low pile sealed commercial carpet with a Sanitaire Wide Track II and it has a boatload of usable CFM when adjusted properly.
Bill
