On Sat, 20 Nov 2004 09:45:25 +0800, Old Nick
wrote:

On Fri, 19 Nov 2004 18:40:08 GMT, "Mike in Mystic"
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

I did some quick plugging in to a little programme I have that does
air flows.

IIRC the 1HP units claim around 600CFM usually? I imagine that the
figure is quoted with NO pipe on the unit. It is complicated by the
need to push the air through the filters.

These may help. I am not sure of the _absolute_ meaning, as it its' a
complex system. Other may elucidate.

But larger pipe is good.

I _think_ that needing to use 2/3 HP to shove 600CFM through 4" pipe
means that power is _lost_ in the pipe, and will represent a dramatic
drop in performance of the DC, due to the fan's being only partially
efficient etc.

If you were using dead straight pipe, then
- 4" pipe up to 45ft long would need 2/3 HP.
- 6" pipe up to 45ft long would need about 1/10 HP.

So pipe diameter is dramatic on long runs.

I plugged in a couple of elbows:
4" pipe, power went from 2/3 HP to around 1.2HP, each elbow was
about .15 HP
6" pipe, power went from 1/10 HP to around 1/6 HP, each elbow was
about .03 HP

Again bigger pipe makes a huge difference.

interesting, nick.. and it makes sense..

I guess the elbow thing is sort of a "damned if you do, damned if you
don't" kind of thing, especially when applied to a cyclone..
I wouldn't want to use my DC without it, but among other issues,
you're adding at least 2 elbows to make it work..