OK, pretty much as advertised. Lower velocity (sqroot) lower the pull, I
guess.

"G. Lewin" wrote in message
...

If you have ONE system, with both 4" and 5" ducts connected in series,
obviously the mass flow rate is the same in each duct. Since the volume
changes little at these pressure differences, the volumetric flow rate
is nearly unchanged. Then the airspeed will go almost exactly like
1/AREA for each section of pipe. Of course, the 4" will cause greater
pressure losses; for equal sections of pipe, the narrower pipe will be
more "lossy." Geez, I wish I could say how much; off the top of my head
I think pressure loss goes like 1/RADIUS^3, but don't quote me on that.
When all my textbooks get out of "storage" (read: the moving van blew
its transmission), I can look it up.

When it comes to "chip carrying energy," if you mean kinetic energy,
well, you know how to find that. If you mean "chip carrying _ability_,"
we'll have to define ability first. Good luck on that one. The best I've
seen is a relationship between airspeed and maximum particle size, but I
can't remember where I saw it. I seem to remember 3000 ft/min. is a good
rule of thumb for wood dust, chips, and fingers.

Greg