The requirements of NFPA-14 for the standpipe hose valves are maximum 175-psi static outlet pressure and minimum 100-psi residual outlet pressure while flowing 250-gpm through the hose valve. If your pump source is from the city mains, then make it easy on yourself and select a PRV hose valve that will provide maximum 165-psi static outlet pressure. This should allow you to use whatever residual inlet pressure while flowing the 750-gpm total standpipe demand and still provide the minimum 100-psi residual outlet pressure.
I used the 165-psi static outlet pressure cause the pump inlet pressure may vary up/down which will vary the pump static outlet pressure which may raise the static outlet pressure over 175-psi. If the pump source has a constant pressure like an elevated tank, then select a PRV that will provide a maximum 175-psi outlet pressure. Just my opinion but if you select a PRV based on the maximum static outlet pressure then this should allow a bit more than the 100-psi minimum outlet pressure. Check the charts to verify this. Don’t select a PRV based on providing just the minimum outlet pressure. I think that the fire department will appreciate any extra pressure to offset the friction loss through their fire hoses. Rick Matsuda > On Oct 31, 2023, at 7:24 AM, Eric Rieve <[email protected]> wrote: > > > Micah, > > Looking at the spec sheet from Zurn I agree with Travis that you use your > expected residual pressure while flowing the full system demand of 750gpm. I > haven’t installed this valve myself, but you’ll notice on the residual > pressure charts that the bonnet type curve lines stop well below 175psi. So, > while you may pick a 120psi outlet pressure while flowing 750gpm, the extra > play in the curve should allow the valve to maintain an outlet pressure below > 175psi when being tested individually at 250gpm. > > Hope this helps! > Eric Rieve, SET > Rieve Fire Protection > > From: Micah Davis <[email protected]> > Sent: Tuesday, October 31, 2023 6:53 AM > To: SprinklerForum <[email protected]> > Subject: [Sprinklerforum] Pressure Regulating Valves Residual Pressures > > Good morning, Forum! I hope everyone is having a great week!! > > I think I got this right, but someone is questioning me. I have an automatic > standpipe with factory pressure-regulating valves (i.e., Zurn 4000). When > calculating residual pressures at the inlet of the PRV to be used in the > sizing charts, the question is, how much water should I be flowing in the > system? One suggestion is only flowing 250 gpm at the hose valve you are > sizing. The other suggestion is flowing the system demand flow per NFPA 14. > In this case, that would be 750 gpm (250 gpm at each of the two most remote > hose valves plus 250 gpm at the top of the only other standpipe). We are in > agreement that the calculation should be a source calc to determine the > actual pressure provided by the system. > > Thank you, > Micah Davis > Ferguson Fire Design > > _________________________________________________________ > SprinklerForum mailing list: > https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org > To unsubscribe send an email to [email protected]
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