which 6" elbow for dust collector piping

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Forum topic by mickeyh posted 01-10-2014 05:23 AM 2550 views 0 times favorited 6 replies Add to Favorites Watch
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22 posts in 2042 days

01-10-2014 05:23 AM

Should I use two 45 degree elbows for a 90 degree turn or one long sweep 90 degree elbow? Has anyone experience with both and notice any different? I looked up SMACNA (fitting pressure drop charts) and the difference is negligible.


6 replies so far

View FirehouseWoodworking's profile


706 posts in 3272 days

#1 posted 01-10-2014 08:01 AM

IMHO, long sweep 90 is the way to go. The fewer the joints, the less chance of something getting snagged inside the ductwork. Good luck.


-- Dave; Lansing, Kansas

View Fred Hargis's profile

Fred Hargis

4986 posts in 2492 days

#2 posted 01-10-2014 12:41 PM

The reason most folks advocate the 2-45’s is that long sweeps aren’t that easy to find. But if you can get them, that would be preferable. Your comment about pressure drop is interesting. I had a cyber buddy with measuring equipment, and he said in measuring the difference between a regular 90º el and the 2-45º els he also observed only a minor difference. I guess if you have several 90’s in a run it can add up, though.

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

View danoaz's profile


222 posts in 2169 days

#3 posted 01-10-2014 01:09 PM

Not a fluid dynamics engineer here, but I wonder if the confusion comes from water association. Water in a pipe turning 90 degrees can create the “bang” you hear from the pressure causing a sudden drop at first but not so much with air because it is a gas and not a liquid. Being a light liquid as apposed to a heavy liquid like propane, it can turn corners more easily. Class dismissed.

-- "Simplicity and repose are the qualities that measure the true value of any work of art." Frank LLoyd Wright

View mickeyh's profile


22 posts in 2042 days

#4 posted 01-10-2014 04:52 PM

Here’s what I found on SMACNA. The pressure drop for a 45 degree elbow is 0.6 that of a 90 degree elbow. Since we need two 45s for every one 90, the pressure drop is 1.2 times that of a 90. I guess I’ll be using 90 elbows instead. A little more expensive but hopefully will be worth it.

If anyone is interested, the site for 6” fittings is under sewer and drain fittings. It’s the cheapest place I can find.

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22 posts in 2042 days

#5 posted 01-10-2014 05:00 PM

Here’s a better image of the SMACNA table:

View KMT's profile


603 posts in 2661 days

#6 posted 01-10-2014 06:19 PM

Great charts mickeyh

-- - Martin

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