AFAIK, moving the dust depends on maintaining a air flow velocity (feet per
minute). If the airflow falls too low, the dust can settle, all you end up
with at the dust collector/shop vac end is a slow stream of clean air.

When you expand the size of the hose from the 2.5" diameter to 4" diameter
hose, the velocity of the 4" section will about 40% of the velocity of the
2.5" section. Unless you've got enough airflow from the shop vac, it would
be likely that it won't have the umph to get the dust all the way from the
tool to the vac.

NOTE: This is all theoretical, as I'm using a shop vac for dust collection,
and haven't played with larger hoses because of this. I thought about
running some PVC or metal runs, but I don't want to do it twice (once for
shop vac, once for the dust collector I know I need).

Clint

wrote in message
oups.com...
So are you saying that you had your shop vac hooked up to the 4" PVC? Or
was your shop vac hooked up directly to the machines? If it was hooked
up
to the 4" PVC, I think I can understand why that would suck (in a bad
way).

How it was:

I had a network of 4" PVC which was reduced back to 2.5 " where the vac
was attached, and at each of the machines. So even though the RAS and
table saw have 4" ports, they were connected to the network by the
smaller hose. I had blast gates at all of the machines.

How it is now:

The vac is still hooked up through it's own 2.5" hose (very short run,
hides in a cabinet) and a blast gate so it can be isolated from the
system when I run the DC. The machine hookups are now 4" DC hose with
4" blast gates, i.e. 4" all the way to the DC. The DC also has a blast
gate so I can switch in the vac for "central vac" use.

The "vac" port in the middle of the shop is still reduced to 2.5" so I
can use standard hose and attachments (it hangs from the ceiling). At
that point, there's about 20' of PVC run back to the vac. I left
another vac port near the drill press for manual cleanup after drilling
plus it can easily reach the work bench for general cleanup.

I'm not sure why you feel that the 4" PVC run would hurt the
performance of the vac?

Tom