"Fly-by-Night CC" wrote in message

The system can only flow as much as the smallest port in the factory
design. Take my Jet 1.5hp for example, what I'm getting at is that the
port and hose from the blower housing to the bag hanging ring is, I
believe, 5" diameter. To my thinking whatever size of the system outside
of the factory setup is limited by this 5" - in other words, one can't
fully draw 6" of main trunk air before the blower through a 5" hose
after the blower - therefore the appropriate size of the main trunk
should be no larger than 5" - or whatever the size of the smallest port
in the manufactured assembly.

Wadya think?

Has to do with velocity. I'm sure others can explain it better. Let's say
your blow has a true capacity of 1000 cfm. It will take in and blow out
1000 cubic feet every minute. If there is no duct at the entrance it will
suck air from any place in the room it can. As you get closer to the blower
you will feel the air moving. The more you restrict the opening, you will
feel the air moving faster. The blower sucks in the air and puts it into a
smaller outlet space and thus adds more force to the air and it moves faster
on the way out. Ducting allows you to concentrate and "aim" the point of
suction.

The blower can move 1000 cfm, but your compressor can make only 4 or 6 cfm,
but when you glow that amount of air through a small nozzle, it feels like a
lot more pressure than the outside of a fan or blower moving much more air.
If the blower did not have enough velocity, the dust would just fall on the
other side and not get moved into the bag. A window fan of the same
capacity with not ducting will move little dust by comparison because it h
as the cfm capacity, but at a much lower velocity.
Ed