Standpipe Hose Valves - Hydraulic Calculation Procedure

[MGXFP]

Hello all.

I've very little experience with standpipes and NFPA14 and would like some help.

The subject is a Class I standpipe. The requirement for calculations are two 2 1/2" hose valves flowing 250 GPM each at a pressure of 100 PSI along with, of course, the top hose valve on all other standpipes flowing the same.

In my calculations I'm not certain whether or not to derive a K factor of 25 for the valve and flow it like a fire sprinkler on the standpipe or to model a short 2 1/2" length of pipe with a friction loss for a mechanical tee.

The difference in pressure isn't great between both methods so I have no concern of not meeting the safety factor but I would like some input from more experienced designers and engineers as to what would be most correct.

Thanks!

 

[TravisMack]

The 100 psi is at the outlet of the valve. Some of the valves have 3-5 psi or more loss across a standard angle pattern hose valve. If you have a pressure reducing hose valve it is a lot more.

Put your 100 psi and 250 at the hose valve, then include the loss through the valve, short nipple and mechanical tee or welded outlet.

That is how I have always done it. Better to be safe than sorry

Have a good weekend.

Travis Mack
MFP Design, LLC

 

[MGXFP]

D'oh. I think I figured it out. Its entirely too simple and therefore confusing.

So 250 GPM are flowing from the valve at 100 PSI, 31 equivalent feet of friction loss through the valve (per NFPA 14), a short length of 2 1/2" pipe and the loss for a mechanical tee.

Thanks for your help!