Okay I'm coming in the middle here but, there is some truth in that. But
not blowing into the hose part.

Listen to the shopvac when you put totally cover the hose end. You wil
notice the rpm's increase.

The blades stalled and are no longer moving air.

Now slowley cover up the hose and you will notice the rpm's drop as load
increases. But again if you totally cover it....

Having the fan blades act like a wing and move air is a load on the
motor. But when the airflow is choked off enough the airflow ceases and
the blades spin with air swirling around them and this has actually less
resistance than when pumping air.

Related reading; compressor stall, blade stall, wing stall, how a wing
works, cavitation.

John



igor wrote:
On Sun, 19 Dec 2004 21:02:18 -0500, wrote:


Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.


Talk about counterintuitive. Hmmmm? So, if I take a house vacuum, run it,
and put my hand over the end for 30 minutes, the motor hardly works, but if
I hook up the outlet of my shopvac to blow into the vacuum's hose the motor
has to work very hard and will overload? Sorry, but I don't get that. --
Igor