Just a quick word of caution...those RPZs are killers on Light Hazard Systems
with low flows. I have to use them here in the Florida Keys due to the
vulnerability of our water system, but if I had a choice I would be using DDCAs.
I just automatically plug in a 12 PSI loss when I'm moving 300 Gallons or less.
John Farabee | Certified Lower Keys Plumbing and Fire | C: 561-707-5150 | F:
305-294-2462
John W. Farabee
561-707-5150
On Friday, June 4, 2021, 04:55:34 PM EDT, Matthew J Willis via
Sprinklerforum <[email protected]> wrote:
That seems correct.
The annex speaks to this.
Elevation above water supply, plus the backflow loss.
There is no other mention of pipe, fittings, etc.
R/
Matt
-----Original Message-----
From: Sprinklerforum <[email protected]> On Behalf
Of Jamie Seidl via Sprinklerforum
Sent: Friday, June 4, 2021 2:14 PM
To: Sprinklerforum <[email protected]>
Cc: Jamie Seidl <[email protected]>
Subject: pipe schedule/residual pressure
I am looking at a project where we are renovating an existing building with a
new system. There are other buildings on the site (1930's vintage) that share
the underground lines. To bring the site into compliance with current codes,
RPZ backflows are being added at the entrance to the site.
The existing buildings are occupied, and the fire department is looking for
some assurance that the systems will work with the addition of the backflow
preventer. I remembered (though have never applied it) section 11.2.2.8 allows
for the calculation of the residual pressure at the highest sprinkler, and
deducting elevation, BFP losses ect... The buildings in question are over 5000
sqft, so the minimum 50 psi will apply.
So my question is, do I just utilize the residual pressure from the closest
hydrant, deduct the elevation and backflow losses from the residual and call it
a day? Or do I need to account for additional friction through the system
piping? Both 13 and the handbook seem to be mute on this.
Thanks again, Forumites.
Jamie Seidl
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