Asking for a friend. If I had a field adjustable PRV hose valve and adjusting, would I be flowing 750gpm at the roof and then open the hose valve and flow another 250gpm?
Sent from my Verizon, Samsung Galaxy smartphone Get Outlook for Android<https://aka.ms/AAb9ysg> ________________________________ From: Rick Matsuda <[email protected]> Sent: Tuesday, October 31, 2023 5:48:25 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: Pressure Regulating Valves Residual Pressures EXTERNAL UNKNOWN EMAIL 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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