Set Standpipe PRV by Flowing One or All Valves?

1/9/2023

We are working on a new (750 gpm) standpipe system.

When testing and setting the field adjustable 2-1/2" PRV hose valves, do you set each one flowing 250 gpm while also flowing 500 gpm elsewhere, to account for the hydraulically calculated design (i.e. lower inlet pressure per NFPA 14-11.5.5.1)?

Or do you just set each one only flowing 250 GPM by itself?

Thanks in advance.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

7 Comments

Dan Wilder

1/9/2023 08:02:11 am

Our testing/Cx went as follows:

Calculations were 2 fold...

Calculation at full flow (750 GPM) - Meets NFPA 14-19 11.5.1.2 & 25-20 6.3.1.1
Calculation at single flow (250 GPM) - Meets NFPA 14-19 11.5.5.1 & NFPA 25-20' 13.5.2.2

Generally the top of the standpipe(s) were standard hose valves so we performed two full flow tests, one at the top and one at the highest level were the PRV's ended.

Generally, those two settings were the same but when they differed, it was a matter of picking a setting that does match both or getting one that met the full flow calculation. We would rather over-discharge a single hose valve than short one but we got the AHJ buy off in writing (the AHJ would rather see a static condition on a hose at 180 PSI vs a residual flowing at 95 PSI).

Fun note, upsize the gang drain at the base and don't use the plastic hoses & clamps on the sprinkler risers - always hard pipe, braided hoses, or copper.....plastic blow off.

Casey Milhorn

1/9/2023 08:11:59 am

I like Dan's method. Very comprehensive. We typically just set ours based on 250 gpm of flow. I think the conversation that Dan had with the fire department becomes even more important when you are outside of the responding departments pumping capacity/elevation. Great question.

sean

1/9/2023 08:31:30 am

it needs to be set by the flow expected downstream of the device

Jesse

1/9/2023 09:00:15 am

I second Dan's approach.

And I very emphatically agree with upsizing the drain.

Bobby Suarez

1/11/2023 01:15:51 pm

NFPA 14 requires automatic class 1 standpipes to provide 100 psi during the full system demand flow not just 250gpm. It clearly states that the hose valve manufactures friction loss should be used in determining the loss through the valve. The PRV manufacturer selection spreadsheet should use the highest anticipated static pressure (static pressure during pump churn) and the lowest anticipated residual pressure ( full NFPA 14 system flow plus friction loss) . In other words the PRV setting should be chosen based on that valve being the last 250gpm of the total system flow. If you dont choose your PRV setting using a similar method you will create a lower floor with a hydraulically more remote demand. Ken Isman's Standpipe Handbook explains this dilemma well.

If you choose your PRV setting in this manner you should have no problem meeting flow requirements in any require scenario.

When we have found this not to be done correctly we found a 30 floor building with more pressure available at the roof hose valves then at the discharge of the ground floor hose valves during the full 750 or 1000 gpm flow.

The same would not be true with a pilot operated PRV but nearly all Hose valve PRV are direct acting and therefore reduce by a fixed percentage and are oblivious to lower than expected inlet pressures. You must choose the setting using the NFPA 14 lowest anticipated residual pressure.

Brian Lukus

1/12/2023 03:48:02 pm

Bobby, In practice to account for the NFPA 14 lowest anticipated residual pressure, do you flow the extra 500gpm when setting the PRV for acceptance testing to drop inlet pressure on the tested PRV? Or do you set the PRV based on the manufacturer curve using the hydraulic calc info, and then just flow test the PRV at 250gpm for acceptance testing?

Bobby Suarez

1/19/2023 10:35:16 am

Brian we require the calculation and valve selection proving that the valve works during full system flow and then we do the acceptance test at 250gpm unless that PRV is one of the hydraulically most remote valves in the portion of the building where the standpipe acceptance flow test will occur. In which case the PRV is flowed as part of the full 750/1000 . For example a few days ago we were acceptance testing a high rise building that has only 2 risers in the upper floors but 3 risers in the lower floors. The lower floors with 3 stairwells have PRVs so those floors flowed their highest PRVs at 4 valves at 1000 gpm and then the roof without PRVs flowed 750 through standard valves.
Rsuarez AT miamiGov dot com

Leave a Reply.

Home
Our Cause

The Blog
The Forum

PE Exam Prep
The Toolkit
MeyerFire University

Pricing
Login
Support
Contact Us

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

MeyerFire, LLC is a NICET Recognized Training Provider and International Code Council Preferred Education Provider.
All text, images, and media Copyright © 2016-2024 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

Set Standpipe PRV by Flowing One or All Valves?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES