# One More Static Pressure Question

 Forum topic by mrramsey posted 10-31-2016 10:57 PM 681 views 0 times favorited 3 replies
 mrramsey33 posts in 1398 days 10-31-2016 10:57 PM I haven’t found a clear answer to this but I questioned myself as I was totaling up the SP for my DC ducting. When do you take a deduction for a Wye? For example my main actually ends up running straight through two two pickups. off of that main are two additional branch lines. Logic tells me that the Wye is calculated on the branch and not the main. In other words on the main I just count the wye as straight pipe since I am not making any turns. -- Mike ~~~ Experience is what you get right after you needed it. ~~~

## 3 replies so far

 Manitario2816 posts in 3685 days #1 posted 10-31-2016 11:04 PM Good question. I calculated all my wyes that come off my main branch even if the air just goes past rather than through. Not sure if this is correct but I reason that the turbulence of the air going past the wye adds to the static pressure even if the air doesn’t directly go through. -- Sometimes the creative process requires foul language. -- Charles Neil mrramsey33 posts in 1398 days #2 posted 10-31-2016 11:24 PM Good question. I calculated all my wyes that come off my main branch even if the air just goes past rather than through. Not sure if this is correct but I reason that the turbulence of the air going past the wye adds to the static pressure even if the air doesn’t directly go through. - Manitario I would agree with that logic but have to think they are not equal. I believe you would only take it on the branch. Take a 6×6x5 wye 5” being the branch. seems to me you would take the 5” wye and add it to the branch. I’m no expert but I have to think on the 6” side the path of least resistance would just get calculated as LF of pipe. . -- Mike ~~~ Experience is what you get right after you needed it. ~~~ crank494032 posts in 3773 days #3 posted 11-01-2016 02:21 AM Well, it can get even more complicated than that. It depends on whether the branch is open and flowing or shut off at a gate farther down the branch. In th latter case, the branch is shut off, if the straight thru flow has a change in diameters to keep it balanced when both lines are open, you actually have some static gain along with a reduction in velocity. Duct systems get pretty hairy to calculate when they have to accomodate multiple branches that can be either open or closed.

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