NFPA 13 makes provisions for the addition of a backflow preventer to a pipe schedule system (i.e., device pressure loss must be taken into account for minimum residual pressure available, per Section 184.108.40.206.2 of the 2019 Edition).
When adding flexible sprinkler drops to a pipe schedule system (1 for 1), is a recalculation necessary, or wouldn't the basic addition of that extra pressure loss to the residual pressure for the pipe schedule system be all that's needed?
The AHJ is requiring a recalculation rather than simply adding the pressure loss to the residual pressure as we would do for adding a backflow preventer.
Thanks in advance.
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7/7/2022 07:30:26 am
We're in MA. Typically, recalculation is required. We use a specific flexible braided hose manufacturer and calculate it at 55 equivalent feet to be conservative. Max length & number of bends.
7/7/2022 08:10:16 am
There is a limit to the amount of modifications made to an old pipe schedule system as still be considered viable. You might have found this AHJ's limits.
I <3 Sprinklers
7/7/2022 08:16:10 am
We would definitely require a recalculation for adding flex drops to a pipe scheduled system in our area outside of very specific circumstances (matching another floor of an existing building that was previously calculated or something like that).
7/7/2022 08:35:26 am
So (spit-balling here, I've worked on about 5 pipe schedule systems in my career), tricky subject as this isn't specifically mentioned in the "Revamping" section and how would you justify pressure loss differences between a hard pipe and a flex hose? If using the SxL x Density to get PSI loss though 1" hard pipe/fittings then applying that to the EQ length of a flex hose, you're effectively applying hydraulic calculation procedures to justify not using hydraulic procedures....
7/7/2022 09:00:49 am
I agree with the AHJ on the need for a calc in this situation (being an old pipe schedule system means it's possibly never had a calculation performed on the system). Water supplies can change a lot over that many years.
7/7/2022 10:18:24 am
I would require full recalc.
7/7/2022 03:09:17 pm
Pipe schedule systems came before flex drops. There's no prevision to using them or not using them per code. That being said I would require a calc as it is not "like for like" replacement or repair. Especially if corrugated hoses was used as those have a higher tendency to crimp and restrict flow as compared to a braded hose.
7/8/2022 07:37:42 am
Every AHJ we deal with would require a full calc. Even if they didn't, I would require my designers to hydraulically prove adequacy before I sealed it.
7/9/2022 09:48:17 pm
7/11/2022 06:28:53 am
you cant mix and match calculation methods either pipe schedule or hydraulic.
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