In article ,
says...
igor wrote:

This comment is not to you so much as to a number of people here who say
that bigger is better with ducts. I can see that as a general proposition,
but at some point, relative to the size of the fan, won't velocity suffer
in a significant way? And, doesn't velocity have a role to play in an
effective DC system? After all, we are not just talking about air -- also
talking about moving solid waste. Or, as is sometimes the case, am I
missing something here? -- Igor

You are actually right on target. Most of the various schemes I've
found for plumbing a single user home shop seem to optimize around a 1
1/2 to 2 HP collector and five inch pipe. Four inch pipe is too
restrictive, six inch pipe slows the velocity too much. So I tend to
get frustrated with all the woodworking suppliers that stock only four
inch pipe, hose and fittings.

So until I can find a big enough crowbar for my wallet, I am still
dragging around the forty feet of four inch flex that came with my
Penn State collector.

But if your running a one man shop, and running only one machine at a
time, does it really matter if the main runs are 4" or 5"? I've got a
delta 1.5 HP DC in my garage shop. I use 4" PVC sewer and drain pipe for
the main runs and flex pipe to the machines. The delta has 2 4" mains
coming off it so I ran 2 runs on each side of the shop. I don't have any
problems with airflow even to the farthest machine, which is a planer.
The PVC was cheap and easy to work. I also didn't bother to ground it
although is does develop some static when I run the planer or jointer.
But I look at it as a dust filter. The suspended dust in the shop sticks
to the pipe. I just vacuum it once in a while.

Just my 2cents.