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Dust Collection related: square to round..loss of CFM?

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Forum topic by Holbs posted 11-08-2018 01:42 AM 490 views 0 times favorited 4 replies Add to Favorites Watch
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Holbs

1983 posts in 2202 days


11-08-2018 01:42 AM

I am in the midst of converting my 3HP dual armed Grizzly DC to blower on top of SSD XL. The dual arm DC is square’ish (4 5/8” x 4 7/8” or something like that). I am having a HVAC friend make me a square to round connector so I can continue the exhaust into dual wynn filters via round ducting.
Watching some forum topics across the web, one person brings up of a CFM loss when going square to round. This is, of course, related to HVAC cfm (which I have no idea what CFM for a/c or furnaces push out). Is there any concerns of drastic loss when it comes to dust collection CFM numbers?

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"


4 replies so far

View Fred Hargis's profile

Fred Hargis

5142 posts in 2666 days


#1 posted 11-08-2018 11:43 AM

Man, it would take some serious lab testing to verify that one way or another. I think you have no problem…but even if it caused some loss there’s not much you can do. Filters are round and your outlet isn’t, I think you’ll have to judge whether you have adequate performance after you’re set up. I’ll say this: there are a lot of DCs that go from square to round on one side or the other (mine does that on both the inlet and the outlet) so I wouldn’t think it’s a big problem or that might not be so common.

-- Our village hasn't lost it's idiot, he was elected to congress.

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Scap

44 posts in 100 days


#2 posted 11-08-2018 12:47 PM

As long as the cross section area is similar, and you’re not introducing a rough or corrugated round pipe to the system, they should flow similarly.

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Manitario

2653 posts in 3056 days


#3 posted 11-08-2018 07:51 PM

It appears that round ducting is actually a bit more efficient, ie. you have to have slightly larger square ducting area to get the same CFM:
https://www.engineeringtoolbox.com/equivalent-diameter-d_443.html

-- Sometimes the creative process requires foul language. -- Charles Neil

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Holbs

1983 posts in 2202 days


#4 posted 11-09-2018 02:49 AM

I talked to a HVAC guy today about this. He said yes, for home HVAC purposes, there is 50-70 CFM loss from going square to round due to the initial turbulence of the transition (if taken from a snaplock 6” duct and making one end square while leaving other end round). But he said for dust collection purposes of high CFM, not to worry about it.
Either way..as Fred says above, gotta do what we gotta do with it, as is.

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

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