This article is from the Woodworking FAQ Collection 2, by multiple authors.
From: guido@twitch.UUCP ( G.Bertocci)
Date: 19 Dec 88 13:35:53 GMT
The max ratings on dust collectors are with ZERO load.
If you add almost any length of pipe the cfm drops dramatically.
I hope that you haven't committed yourself yet, however, 4 inch piping
is going to limit you to about 350 cfm almost regardless of the size of
the motor you have. (350 cfm is marginal for some applications).
Having just completed what I would almost consider a thesis in dust
collection equipment, I made a number of plots showing cfm vs static
pressure (as a function of pipe diameter). The result was rather
interesting, each pipe diameter essentially dictates the max cfm
almost entirely regardless of the motor size. The problem is that
the max static pressure on dust collectors is in the range of 5 - 10 inches
of water (shop vacs are in the 50-100 inch range).
As a result, as soon as you start to make a permanent installation with
piping you hit the limit cfm for each pipe diameter.
3 inch - ~180 (I don't have my plots in front of me so these are
4 inch - ~350 recollections. )
5 inch - ~600
I got a lot of information from Air Handling Systems in CT. who sent me
a dust collection calculator (paper slide rule gadget) and
Cincinnatti Fan Corp (they make Delta dust collectors).
One of the final conclusions that I came up with was that 5 inch pipe
is about ideal for a home shop and this was verified by an engineer
at Cincinnatti Fan. With 5 inch pipe and their 2 HP dust collector you
could run about 100 equivalent linear feet of pipe and get about 600 cfm.
* As a side note, I have not purchased anything yet, I have just
researched it to death.
For your static electricity problem, drill 2 small holes in your PVC pipe
every 4-8 feet and run the wire inside your pipe and then out and back
in the two holes and then on to the next pair of holes.
This has the effect of helping to keep the wire as close to the wall of
pipe as possible. Afterwards plug the two holes with silicone.