Need some expert opinions on wye angle

[John Donofrio]

Got home tonight to find the shipment of 6x6x6 flue wye's from HD on my front porch. The price was right and the quality of construction is good. I read in another post where someone used them and said the branch angle was closer to 60 degrees as opposed to 45. I find them to actually be closer to 70 degrees which brings me to the question... Is this too sharp an angle? I don't want to go through installing all this ducting only to find I have destroyed the performance using bad fittings.

I'm pretty bummed right about now. Hopefully there's good news, but I doubt it.

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[Mike Henderson]

I'm no expert but that looks okay to me for dust collection.

Mike

[Michael W. Clark]

You are probably looking at about another 0.2"wg of SP loss per fitting as opposed to a 45 (assuming 4000 FPM duct velocity). Maybe not "perfect" (what system is?), but certainly not a deal breaker assuming you don't have several of these connected together for running one machine/branch.

Clarifiaction: This loss is only seen when you are pulling through the "branch" of this fitting. If you are running "through" the fitting, the loss doesn't apply.

Mike

[Morey St. Denis]

"the loss doesn't apply"?.. I'd be quite interested to learn when the Bernoulli equation does not apply along the streamline to that mass portion of a moving fluid undergoing the diversion. A partial loss in kinetic energy due to inconvenient geometry is an unrecoverable loss of energy to the system as a whole, without a substantial change in altitude or any added input of energy to compensate.

[Mike Heidrick]

Didn't you make design decisions based on cost anyway in your last thread? Id not worry about a few degree diff in a wye when you sacrificed your mainline dia for cost. Perf is not your main concern.

[John Donofrio]

Didn't you make design decisions based on cost anyway in your last thread? Id not worry about a few degree diff in a wye when you sacrificed your mainline dia for cost. Perf is not your main concern.

Yeah, that's about right but I don't want to totally kill performance. I will spend if I have to. As usual I'm trying to walk the line of price/performance. Initially these wye's felt to me like the performance hit might be too great but after these responses I feel a bit better. The shop is only 22x22 and the two drops that run to the other side of the room are floor sweeps (and/or vac connections) so the system should have a little head room where it matter most. On the plus side too is the fact that no one run length from tool to cyclone is more than about 25 feet in total length.

You are probably looking at about another 0.2"wg of SP loss per fitting as opposed to a 45 (assuming 4000 FPM duct velocity). Maybe not "perfect" (what system is?), but certainly not a deal breaker assuming you don't have several of these connected together for running one machine/branch.

Clarifiaction: This loss is only seen when you are pulling through the "branch" of this fitting. If you are running "through" the fitting, the loss doesn't apply.

Mike

As the plan stands now there will only be a couple places where a run goes through more than one of these 6x6x6 wye branches but never more than two. Unfortunately one of them is at the table saw but I may be able to change that. In any case there will always be at least one wye branch involved since these are the branches for the drops. I'll wait to see how many CFM I am getting there once it's hooked up and adjust if I can.

[Bill Adamsen]

John:

I've attached photos of 7" x 6" x 6" wye I purchased from Spiral, and the difference in manufacturing is worlds apart. Cost probably too. I'm happy I spent the difference.

Wouldn't worry about the angle ... just put the system together and use something to minimize air leaks.

[Michael W. Clark]

"the loss doesn't apply"?.. I'd be quite interested to learn when the Bernoulli equation does not apply along the streamline to that mass portion of a moving fluid undergoing the diversion. A partial loss in kinetic energy due to inconvenient geometry is an unrecoverable loss of energy to the system as a whole, without a substantial change in altitude or any added input of energy to compensate.

Morey, The losses are the difference in dynamic losses (not frictional) for turning the airstream. If you are not pulling through the "branch" side, and are pulling through the "run" side, then there is no difference between this fitting and one with a 45 take-off or a straight piece of duct, so these losses would not apply. You still have straight duct frictional (Bernoulli/Moody factor) losses through the straight duct. Frictional losses are calculated on the duct CL through all fittings.

I wrote the clarification to my post because the OP may have several of these that branch off to different tools. The dynamic loss will only count in the fittings where air is being pulled through the branch side of the fitting.

You can also look at this as a mitered elbow and may be the more correct way to do it. In this case, you have about 0.35"wg more loss than a 45 mitered elbow (@ 4000 FPM). Either way, its fractions of an inch, and would be considerably more trouble to change vs the potential benefit in my opinion.

FYI, a 30 degree tee-on-taper is standard for true dust collection fittings. As has been stated before, we are all trying to adapt ducting and piping designed for another purpose to this application, so there will be inherent compromises.

Mike