6” or 7” ducting?
#18
(09-14-2022, 07:10 AM)fredhargis Wrote: Believe what you want, nio skin off my nose. But that 8" port was put there by the same guys who claim it moves 2700+ CFM. Nuff said.

fred - you'd almost certainly be wrong
Yes

If you'd look a bit more closely at LT's marketing fluff you'd see they also state the real world , or connected airflow is 1600 cfm +/-.
So, what's more likely:  the guy in marketing coming up with the 2700cfm # or the fluid dynamic engineer that designed the cyclone with an 8" port ?

If you'd care to look at Cliff's V-3000 spex , you'll notice it has a 7" inlet - which is what their duct designers suggested he go with.  Pretty safe to assume they know he has tools with 4" (or smaller) dust ports.  If  6" were as good or better, don't you think they'd have mentioned that being that 6" pipe and fittings are much easier to source ?

Quote:I would suggest a 6" main trunk, and run 6" as far as it will go...to the point of modifying the tool's ports to take a 6" in every case possible.

This is not how good dust collection pipe networks are designed.  The main line is bigger than the branch lines, sub branches taper again if necessary.


Quote:With a 3 HP dc, 6" would be plenty anyway
Adequate or acceptable would probably be a better word choice.   Especially not knowing all the other variables in the equation.


Bottom line is that saying just use "x" inch duct and you'll be good is short sited.
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#19
Juss1, what ever you decide to do please post back and let us know how things worked out. BTW, you might find this by Wood Magazine to be of interest, maybe even useful.
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.
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#20
The proper way to go about it is to look at the velocity required and actual cfm of the DC. For 3 hp I'm pretty sure 6" mains would be the correct size for most layouts.

Do not just go by the stated cfm of the unit. You need to look at the fan curve and see what it is at the pressure drop you expect at the machines. Also, flow will drop as your filters or bags load up.

John
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#21
How do you calculate what the expected pressure drop will be at a machine for a given pipe diameter.  I have an Anemometer so I can measure the actual cfm at my DC.  Below are the specs for the current model of the PFlux.  I have an older model and am checking with Laguna but I think I read somewhere these values still hold true.

[Image: PFlux3-Performance-Chart-1.jpg]
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#22
Based on the table above and the parameters they used (8” flexible hose at 128” long) it seems like 8” provided the largest cfm and fastest velocity. Unless I’m missing something and didn’t read it properly?
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#23
The stated cfm is based on a standard test. The fan curve shows what the actual flow will be for different pipe diameters and static pressure. You calculate the expected pressure drop by looking up the values for the pipe and hose diameters you want to use, times the length of each. You add to that the pressure drop for every 45 and 90 deg elbow. It's not by guess by gosh. You just have to do the calculations. There are plenty of good online resources on how to do it.

John
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#24
Industry sources suggest Sawdust, small wood blocks, and sand blast dust, should have a velocity of on the order of 4500 FPM, or 50MPH to remain suspended in the air flow.   An 8" duct moving 2700 CFM would have a velocity on the order of 90MPH or 8100 FPm, so suspension should certainly not be a problem.   It is important that minimum velocities be maintained to avoid system problems.  
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