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Hydrant Orifice Coefficient

Hydrant Orifice Coefficient

Hydrant Orifice Coefficient

(OP)
When doing flow tests, I was always taught to feel the inside of the hydrant butt, record the shape, and apply the correct coefficient in my flow calc - 0.7 for protruding edge, 0.8 for square corners, and 0.9 for rounded corners.  When referring to my "quick convert" pitot charts, a discharge coeffiecient of 1 is always used.  

My question is, am I seriously shortchanging myself when subtracting 20% (i.e  0.8 for square corners)in the flow calc?  

Any insight would be greatly appreciated.

...using Q=29.83cd^2p^.5 where c is the variable in question...

RE: Hydrant Orifice Coefficient

I always use the formula.

I've never seen a hydrant with square corners.  I am aware of the .80 for square corners but I've never run across any.

 

RE: Hydrant Orifice Coefficient

Ditto to SD2 comment. I have never seen a hydrant orifice with square corners.

RE: Hydrant Orifice Coefficient

Your quick convert charts are likely giving you "theoretical" numbers.  You are then to make the conversion based on your flowing outlet.  Also, don't forget that if you flow the pumper outlet, you have to made additional modifications per NFPA 291.

Travis Mack
MFP Design, LLC
www.mfpdesign.com
 

RE: Hydrant Orifice Coefficient

(OP)
SD2 et al...

as usual, I leave this forum smarter than when I came.

Thanks for the responses.

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