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Friction loss for reducer in sprinkler calculation

morgan.z

Civil/Environmental
Aug 3, 2018
28
Can somebody please shed light on me about friction loss calculation for reducer in sprinkler calculation: NFPA 13 mentions elbow reducer in hydraulic calculation, but miss out on the equivalent length for reducer.It is common to use reducer after a tee in the branches. it is said equivalent length is not fit for reducer in some case . Do we need to calculate the friction loss for reducer in sprinkler pipe?
I look up other handbooks, a 3"/2" reducer is about 3 feet equivalent length , seems too big too ignore.
Really appreciate your help!
 
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Hydraulics for fire sprinklers are not like other hydraulics. For example, the turn of sprinklers directly screwed to tees or elbows is already accounted in the sprinkler K factor and therefore ignored. That typically includes the reducer as well. An other reason for such allowance is the hazen-williams equation which introduces error always on the safe side.
 
Thanks for your explanation.
i have not seen software like Elite fire has a equivalent length for reducer, not sure if to put in added equivalent length to the pipe. the NFPA 13 has mentioned the sprinkler nozzle directly screwed fittings to tees or elbows, reducer, but it says nothing about reducer in other places.
So i can interpret it that even the reducers after a tee in the branches DIRECTION can be ignored?
 
Fittings like reducers incur hydraulic losses called minor losses. Typically, NFPA 13 does not require the designer to include minor losses in the calculation process. As UFT12 said, any fitting the sprinkler is installed in has the loss accounted for in the K-factor. Otherwise, we do not figure these losses in our calculations. Typically, I will include a hydraulic node at the point where pipe sizes change in the case of a reducing grooved coupling on a main and carry the calculation forward with the different pipe size. If you have a reducing fitting like a reducing tee, NFPA 13 says to use the equivalent length associated with the smaller pipe size.
 
I got it: for pipe sizes change in the main using such like a reducing grooved coupling, a node is made, but not necessarily to calculate the friction loss of this node.
With your extra explanation, it is well understood!
Thanks!
 
So NFPA 13 does say to include the loss through fittings, but does not include any reducing fittings to include where water does not change directions to figure friction loss. It says if you have the loss to include it. So, I'd say if you have manufacturer data, then including that in your calculations is a good idea.
 
I sometime use AFT phantom software to do both sprinkler and other hydraulic system calculation - it may not be a typical fire water spray calculation software, it has reducer model built in, that is why i have above thoughts .
Thanks for the further clarification.
 

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