What I think you should do is adjust/select the PRV to provide a maximum static outlet pressure of 175-psi based on whatever the maximum static inlet pressure is. See the Zurn static pressure chart.
This is correct. Setting should be based on maximum static condition. Then use the 250-gpm flow rate chart to determine what your outlet pressure will be at that flow rate. Also correct. The 175-psi static outlet pressure should give you enough safety to meet the 100-psi minimum residual while flowing 250-gpm even if you open all four hose valves. Probably, but not necessarily. There can be a very large difference between the maximum static pressure (city static plus pump churn, minus elevation) available versus the pressure available with 1,000 GPM flowing (city residual plus pump residual, minus elevation and minus friction loss). A steep city flow test that drops off quickly can exacerbate the issue. Also, you may be required to subtract a safety margin (10% or 10 psi or something) from the flowing pressure. You can run into a scenario where the topmost PRV can’t produce 100 psi without increasing pump pressure, but then increasing pump pressure requires another level of PRVs, and you just need someone with some common sense to intervene on your behalf. I’m not an Autosprink user, but when I run these calcs I look at the 250-GPM flow chart as mentioned, and look at the curve for the setting that was dictated by the static chart. Then I look at what inlet pressure is required in order to get the required outlet pressure of 100 psi, then use the difference as a fixed loss at the hose valve. Then I set the hose valve(s) to require a flow of 250 GPM at a pressure of 100 psi and run the calc. -Kyle M From: Rick Matsuda <[email protected]> Sent: Tuesday, May 2, 2023 11:11 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [EXTERNAL] [Sprinklerforum] Re: help August, I’m not familiar with the ZurnW5000 model PRV. As best as I can remember, Zurn made a field-adjustable and a factory-set PRV. What I think you should do is adjust/select the PRV to provide a maximum static outlet pressure of 175-psi based on whatever the maximum static inlet pressure is. See the Zurn static pressure chart. Then use the 250-gpm flow rate chart to determine what your outlet pressure will be at that flow rate. Yes, the residual pressure will change based on the number of hose valves that you open but at that point the fire dept should already be hooked up to the FDC to pump additional pressure if required. The 175-psi static outlet pressure should give you enough safety to meet the 100-psi minimum residual while flowing 250-gpm even if you open all four hose valves. Regarding you second question, I don’t know of any hydraulic calc program that will calculate through the PRV. The outlet of your the PRV for sprinklers is a new “hydrant test” with a new static pressure (max 175) and residual outlet pressure from the charts while flowing 250-gpm. A good rough guess would be to use static 175 and residual 100 while flowing 250-gpm as your new supply point which is what the hose valve requires. Rick Matsuda On May 2, 2023, at 12:34 PM, August Hoffman <[email protected]<mailto:[email protected]>> wrote: Hello, I am a little confused on calculating PRV hose valves and could use some help getting an answer. I have a standpipe system with two standpipes fed by a pump; the lower floors require PRV hose valves due to higher pressure on the lower floors. We are using the ZurnW5000 PRV hose valves for reference. We need to add a new hose valve on one of the lower floors that require a PRV hose valve. For this we are required to flow 750pgm off that standpipe as well as 250 off the other standpipe. The 750gpm will include the new hose valve. 4 Hose valves all flowing at 250gpm total. So far all good, no confusion. Now the PRV setting is dependent on available pressure, if I were to determine the setting based on just one hose flowing it would be different than if I were to have 4 hose valves flowing. My question is - What do I do to determine the setting? Do I flow one hose at 250gpm to get the setting, then calc all 4 with their individual settings to make sure the system works? Or do I flow 4 hose valves to determine the settings accordingly? My issue is - If I use the setting for just one hose flowing and in the field they need to flow 4 then they will not have enough pressure at that hose. If I use the setting from 4 hoses being flowed and in the field they end up flowing just one hose then there will be too much pressure flowing from that hose. Second question - This mostly is for any AutoSprink users, how would you input these settings? I have tried it 2 ways getting very different results. The first test was setting the minimum pressure @ the PRVs residual pressure (say setting 14 takes my 194psi RES. down to 154psi RES so I set my min. pressure to 154). The second test was to keep my minimum pressure @ 125psi but subtract 154 from 194 and adding 40psi loss to my hose valve. The second test seems to make the most sense to me but I heard to do it both ways from different people. I appreciate any advice. Thank you, August Designer NICET WBS 153613 _________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]<mailto:[email protected]>
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