Hydrant Orifice Coefficient

[skdesigner]

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...

 

[SprinklerDesigner2]

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.

 

[stookeyfpe]

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

 

[TravisMack]

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

http://www.mfpdesign.com

 

[skdesigner]

SD2 et al...

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

Thanks for the responses.