This may be entirely elemental to many of you, but it has been something I have wondered about for some time: what is the relationship of the suction power of a machine to its degree of air flow? Could one machine have greater suction than another but not greater air flow?

Ristenbatt Vacuum has an article (see link) on air flow that does a fairly good job of explaining airflow, suction and resistance to airlow in the vacuum cleaner system. The article includes links to other articles (see article on fan or impellor types) and a glossery of terms. So, to answer your question, yes -- when you consider the resistance to the airflow in the system. Traditional "direct air" uprights have tremendous air flow but less suction than a "clean air" canister.

...I want to emphasize (and possibly clarify) what they said about nozzle size, though.

Most household vacuum cleaners use a 1-1/4" diameter hose. If you can find two vacuums that have the same suction pressure at that 1-1/4" hose opening (or, just inside the hose opening) then they will both have the same airflow through their hose openings. Always.

However, once you change the size of the opening, all bets are off. A shop vacuum that could achieve the same suction pressure at the opening of a 2-1/2" hose would have dramatically higher airflow.

Suction is also knows as water lift. That's the pressure that the motor's fan (or fans) develops. Air-Flow is the amount of air moving through the machine. The filter (or bag) will restrict the airflow through the machine, as well as the clogging effect of dirt. SO, a vacuum that advertises good airflow ratings, can ONLY do so for a moment, when brand new. As soon as dirt is inhaled, the airflow begins to diminish. Airflow picks up dirt, suction (water lift) is the pressure to pull it quickly into the machine. Some vacs have great airflow with low water lift (Rainbow). Some have great pressure with low airflow.

The truth is: if the vacuum has good airflow and water lift, then it will clean well. IF the machine doesn't lose its airflow (Rainbow, Dyson, etc.) then it's an excellent machine at cleaning CONSISTENTLY. A vacuum with high airflow and water lift at first, but clogs quickly (Hoover Windtunnel 2 bagless) cannot continue to clean well for a long time and will, in fact, stop cleaning deeply very quickly. Hence the reason that Electrolux told us (in the model G's owners book) to change the bag before EACH USE.