Michael- If you go to
Bill Pentz site I believe he has the info on computing DC/duct performance. You will note that both pipe (length and diam.), which you don't have much control over, and fittings (the number of bends and severity of the angle) are the factors that affect performance.
First, I need to add a little bit about DC performance- realistically there are two types (1) cleanliness-does the DC suck up most of the chips and dust? (2) heath- does the DC remove the majority of fine, airborne, unhealthy, dust- at the machine and does the dust reenter the air because you are using a typical (overly porous) fabric filter bag that is located in your shop? Though both aren't mutually exclusive, many woodworkers, me included, too often value (1) over (2). Bill Pentz's site is focused heavily on (2).
That being said here are some general guidelines for both types of performance for a whole-shop setup which it looks like you are installing:
- Pipe should be sized for the blower (motor hp and impeller diam.)- generally no smaller than 4", and preferably 6" (or larger), for max CFM and to meet the needs of the typical WW machine.
- Keep duct as large as possible, as long as possible, right up to the machine.
- Limit the use of flex hose
- The blower should be minimum of 2 hp w/12" impeller and preferably 3-5 hp, w/14" impeller
- Runs should be as short as possible, with minimum bends. Instead of running pipe around the perimeter of a shop- run it down the center or diagonally, have two mains instead of one long meandering run.
- Where bends are necessary, they should be gentle, sweeping, large radius bends. Use wyes (NEVER "T's"), 45's, and as few 90's as possible. Use smooth, fixed, long radius bends if available rather than adjustable radius bends due to the irregular interior. If it gets you a larger radius use two 45's vs one 90. In simple terms you want as few turns as possible.
- Seal all CFM-stealing leaks
One other suggestion- assemble your duct system so you can easily take it apart- it is not a question of
if you will reconfigure, it is
when. Don't use duct tape- goes bad and leaves residue. If you use tape, use the foil type that HVAC guys use. Silcone works very well on both metal and PVC duct. I friction-fit all my pipe-fittings, used very few screws, and once assembled added a very small bead of silicone to the
outside of the fittings. Just a tiny bit of silicone caulk applied to the
outside of pipe/fitting joints will seal well (remember, the pipe is under suction). The silicone doesn't bond very well so you can rub it off with your fingers- makes it easy to reuse the pipe and fittings.