I know this is an old post but.... Look at NFPA 13 -2019 edition:
19.3.2 Water Demand Requirements — Pipe Schedule Method. 19.3.2.6* Residual Pressure. 19.3.2.6.1 The residual pressure requirement of Table 19.3.2.1 shall be met at the elevation of the highest sprinkler. 19.3.2.6.2 Friction Loss Due to Backflow Prevention Valves. 19.3.2.6.2.1 When backflow prevention valves are installed on pipe schedule systems, the friction losses of the device shall be accounted for when determining acceptable residual pressure at the top level of sprinklers. This requirement has been in the standard for many years. *The above is my opinion and has not been processed as a formal interpretation in accordance with the NFPA Regulations Governing Committee Projects. This is provided with the understanding that the AFSA assumes no liability for this opinion or actions taken on it and they are not to be considered the official position of the **AFSA, and/or NFPA or its technical committees.**AFSA cannot provide design or consulting engineering services, and this opinion should therefore not be considered, nor relied upon, as such.* Thanks, John John August Denhardt, PE *Vice President, Engineering and Technical Services* *American Fire Sprinkler Association* m: p: 301-343-1457 214-349-5965 ext 121 w: firesprinkler.org <https://www.facebook.com/firesprinkler.org/> <https://twitter.com/afsa/status/1039528345367732224> <https://www.linkedin.com/company/american-fire-sprinkler-association-afsa-/> <https://www.instagram.com/firesprinklerorg/> *Our members are at the heart of everything we do* *Train a safer, more efficient workforce.* By enrolling your employees in the AFSA Apprenticeship Training Series for Sprinkler Fitters <https://www.firesprinkler.org/WWW/Education/Apprentice_Training/WWW/Education/Apprenticeship_Training.aspx?hkey=e88ef09e-d74c-407f-abcd-995aff866149>, you will reap the benefits of a qualified, professional installation crew. Well-trained employees will work smarter, increasing your company's productivity and, in turn, its profits. Learn more <https://www.firesprinkler.org/WWW/Education/Apprentice_Training/WWW/Education/Apprenticeship_Training.aspx?hkey=e88ef09e-d74c-407f-abcd-995aff866149> . On Mon, Apr 19, 2021 at 11:56 AM J H via Sprinklerforum < [email protected]> wrote: > Yeah, I've done it before but wanted to see if I had been doing it > correctly. I don't like to hydraulically calculate a pipe scheduled system > as I've often seen the calcs bust causing even more headache for everyone > when it's not necessary if the pipe scheduled 'hand calc' method works - > not to mention they're two totally different sizing methods. As it turns > out this particular project is busted by both the pipe scheduled 'hand > calc' method and hydraulic calculation method so it's become a non issue - > the owner will have to modify his system in order to reduce friction loss > to the point where it can be retrofitted with a backflow preventor. > > < > https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon > > > Virus-free. > www.avast.com > < > https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link > > > <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > > On Wed, Apr 14, 2021 at 12:36 AM Fpdcdesign via Sprinklerforum < > [email protected]> wrote: > > > > > > > > > I have done a few of these. I am not sure about 2019, but 2016 main and > > appendix describe how to do this. You are pretty much in the right track > > > > > > > > > > > > > > > > > > > > > > On Apr 13, 2021 at 6:51 PM, <J H via Sprinklerforum (mailto: > > [email protected])> wrote: > > > > > > > > > > > > Any takers? Does anyone retrofit backflows onto pipe scheduled > systems? > > On Mon, Apr 12, 2021 at 2:43 PM J H <[email protected] > (mailto: > > [email protected])> wrote: > Hello All, > We're > > retrofitting a double check into an existing pipe scheduled system. > > In > > looking at NFPA 13 (2019) edition 19.3.2.1 in order to do this we just > > > need a hydrant flow test and then subtract the friction losses of the > > > double check and the friction loss due to elevation of the highest > > > sprinkler from the flow test and make sure the leftover pressure is > > greater > than the value of 19.3.2.1. Is that correct? > > JH > > > > > _______________________________________________ Sprinklerforum mailing > > list [email protected] (mailto: > > [email protected]) > > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > > > > > > > > > > > > > > > > _______________________________________________ > > Sprinklerforum mailing list > > [email protected] > > > > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
