Upsizing Dust Collector Port

Hi,
I'm about to buy a dust collector that has a 4" port. I've read some posts that suggest not using 4" ducting in the shop but to use 5" or 6" ducting and then reduce to 4" at the dust collector and at the machines.
What is the point of going from a 4" port on the dust collector to 6" pipeing? Is this more efficient?
Thanks
Alex
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snipped-for-privacy@rbc.com wrote:

It's all about friction. The friction of the air moving along the pipe walls slows the air down. The air has to move faster in the smaller pipe than it does in the larger pipe, so friction losses are greater. The air can speed up to pass through a short section of smaller pipe without much loss. The longer the section of small pipe, the greater the friction loss.
However, you must be careful not to use too large a pipe, or the air will slow down too much in it and allow the chips to fall out. See Bill Pentz's very informative web site http://billpentz.com/woodworking/cyclone/Index.cfm
DonkeyHody "If your only tool is a hammer, you tend to see every problem as a nail." - Abraham Maslow
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Doesn't it also help to prevent clogs where you won't be able to get to them? In that if it's small enough to fit through the 4" port, then it should be able to make it through the rest of the system without too much trouble?
-Nathan
DonkeyHody wrote:

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After doing a lot of research I found that going with a 5 inch pipe for the long runs and reducing to 4 inch at the collector seems to work for me in my basement shop.
len
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snipped-for-privacy@rbc.com wrote:

Yes, but...(there's always a "but" :) )
You have to be sure you have sufficent volume capacity in the collector to retain a minimum linear velocity, not just cfm. For fine dust and chips, 3000 fpm may be adequate but for a planer or jointer w/ larger chips, 4000 fpm is nearer a minimum for adequate performance. Remember area increases by square of diameter, so the linear velocity drops pretty quickly.
The basic ideas of wall friction and all in another response are ok, but note that a single reducer or elbow or wye or tee as the effective pressure drop of several feet of pipe. If this is a single-stage collector w/ a single 4" duct, I'd wager anything greater than 5" will definitely be too big.
The last issue of "Shops and Tools" from Fine Woodworking has a nice overview where they evaluated volume and linear flow rates from a variety of collectors and prepared some comparative figures showing what you can expect from various-sized single- and two-stage collectors from 1-1/2 to 3+ hp. I assume you may be able to find the article online at www.taunton.com, perhaps. If not, it would definitely be worth a trip to the library and if you're serious, probably the few bucks at the newstand.
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I got the specs for the dust collector I'm going to buy. It will only be running one machine at a time and I have a pretty small shop. The longest stretch of ducting will be 15'.
It is a 1 HP 600 cfm machine. From that is there a formula I would use to figure out the correct size of ducting?
dpb wrote:

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Is that a special issue or something? I am looking to buy a cyclone and they are sufficiently expensive to justify a little research. Thanks.
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If it only has a 4" port it is probably such low capacity that there would be little advantage to upsizing.
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