With all due respect Rick, I have had Fire Departments very concerned about the residual pressure being greater than 100 psi for safety.
Sizing PRV's is not the easiest part of a standpipe design. If you are in a jurisdiction that requires flow testing and recording the pressures prior to the final inspection (as it should be per NFPA 14), guessing could cost a lot of money to correct. On Tue, Oct 31, 2023 at 10:49 AM Rick Matsuda <rick26...@gmail.com> wrote: > 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 <e...@rievefire.com> 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 <micah...@gmail.com> > *Sent:* Tuesday, October 31, 2023 6:53 AM > *To:* SprinklerForum <sprinklerforum@lists.firesprinkler.org> > *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 > sprinklerforum-le...@lists.firesprinkler.org > > > _________________________________________________________ > SprinklerForum mailing list: > https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org > To unsubscribe send an email to > sprinklerforum-le...@lists.firesprinkler.org -- Greg McGahan *Genesis Fire Services, LLC* *4912 Glover Lane. Milton, FL **32570* *P- 850-637-8535* *C- 850-712-9555*
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