Italian fellow name of Bernoulli, I believe, has some good words to say on
the subject.

Consider the original force per unit area I mentioned. That's where the
term PSI comes in. You can haul more air through a larger pipe, but the
pressure drops, because you're not capable of real compression through the
open sides of the impeller. This means that what's being carried along with
the air will also drop. Reverse is also pretty true. Take your 4" hose,
as I often do, and use a standard shop-vac adapter to 2", and notice you can
pick up pencils, chunks of scrap, and even the bolt you dropped, and were
looking for. Don't be frustrated and think you'll have to rummage through
the cyclone, those things are just upstream of the adapter, if they made it
that far, where there is no longer enough force/unit to carry them into the
bin. I rely on this when looking for dropped objects in my shop.

As mentioned, the "standard" unit now moves 1200/CFM at (some PSI) or in
reality, at some vacuum, measured in feet of water, inches/millimeters of
mercury or furlongs per fortnight. Now since the old 650 CFM @ 8 types were
the standard which spawned the 4" hose, I'm speculating that a 5" hose may
be best for the 1200, because the impellers are still pretty leaky, if you
read the mfrs specs. A 6" hose, as mentioned, would be 2 1/3 or so times
the area of a 4, negating the additional chip-carrying power.

Oh yes, don't ask about 2" hose and 2" sanding discs for the lathe. Makes
me veeery angry.

"Fly-by-Night CC" wrote in message
news
In article , "George" george@least
wrote:

Not an engineer, but imagine the optimum transport pipe is probably ~5".
Force/unit area calcs show 6" less than half the four.

Perhaps someone can point out the error of my thinking on this subject...

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?