The first thing to do is look at the RPZ’s flow rate/pressure loss chart to see if it is operating as the manufacturer says it would based on what the supply test indicated. The RPZ might be undersized. If there still appears to be more pressure loss than expected, test the inlet and outlet at flow. That will tell you if there is something upstream that is unaccounted for, like a valve not fully open or a water company device or if the RPZ is at fault. Things happen. For example the site underground main installer might have done work on the underground supply subsequent to the initial flushing and testing that others are not aware of. In which case there might be rocks in the RPZ. Sometimes an underground valve is simply operated without counting the turns to know it appears to operate like it ought to.
> On Jun 24, 2025, at 11:54 AM, Fpdcdesign <[email protected]> wrote: > > Interesting point. You would need to monitor the inlet pressure to the BFP as > well as the “suction” pressure. > > However, according to the purveyor’s flow test, there should be approximately > 38 psi with a relatively flat curve. If you are losing 23 psi through a > backflow preventer flowing a few hundred gallons, there is a problem. > > Caveat: I was asked my opinion because my client was questioning some else’s > recommendations. Not formally a job to solve. > > Todd Williams > Fire Protection Design/Consulting > Stonington, CT > 860-608-4559 > > >> On Jun 24, 2025 at 12:39 PM, <Rick Matsuda <mailto:[email protected]>> >> wrote: >> >> Where are you reading 15-psi? >> >> If it’s before the RPZ backflow preventer, then check with the local water >> utilities to see what they recommend. Creating pressure below 20-psi in the >> city supply is not a good condition. >> >> If it’s after the backflow preventer at the pump suction flange, then I >> don’t think it’s a problem as long as you don’t drop below 0-psi. >> >> Just my honest opinion >> Rick Matsuda >> >>> On Jun 24, 2025, at 11:20 AM, Christopher S. Wilson <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>> Does this only happen when you take the pump to 150%? >>> >>> >>> >>> >>> Christopher S. Wilson >>> Project Design Manager, SET >>> >>> <treasure-valley-pb-350-1.0_43d4236b-9650-46f6-b30d-8de3f28cb36e.png> >>> (208) 872 1128 <tel:(208) 872 1128> >>> [email protected] <mailto:[email protected]> >>> >>> Treasure Valley Fire Protection >>> A Pye-Barker Fire & Safety Company >>> 2731 Saturn Way >>> Boise, ID 83709 >>> >>> >>> <036_sm_in_468e365e-e301-4c97-a0b4-805cb9a8926e.png> >>> <https://www.linkedin.com/company/pye-barker-fire-&-safety> >>> pyebarkerfs.com <http://www.pyebarkerfs.com/> >>> >>> >>> From: Fpdcdesign <[email protected] <mailto:[email protected]>> >>> Sent: Tuesday, June 24, 2025 10:17 AM >>> To: Discussion list on issues relating to automatic fire sprinklers >>> <[email protected] >>> <mailto:[email protected]>> >>> Subject: [Sprinklerforum] Re: [EXTERNAL] Backflow turbulence >>> >>> The water supply tested in the street to 38 psi with less than 5 ft >>> elevation to the pump room. The suction pressure they are getting during >>> the pump test is 15 >>> >>> Todd Williams >>> Fire Protection Design/Consulting >>> Stonington, CT >>> 860-608-4559 >>> >>> >>> >>> On Jun 24, 2025 at 11:39 AM, <Craig Prahl <mailto:[email protected]>> >>> wrote: >>> >>> Are suction pressures low due to the water supply? Since there is a BFP, I >>> assume you’re drawing from a city service, correct? Got any data on that >>> system? >>> >>> Craig Prahl | Jacobs | Fire Protection SME – EV, AM, DC, Special Hazards >>> [email protected] <mailto:[email protected]> | www.jacobs.com >>> <https://urldefense.com/v3/__http:/www.jacobs.com/__;!!KZTdOCjhgt4hgw!-_khxU8gU0_6jc895I7kRbnU8JghRDsWgqOblZ4jr7Qp2IVbR30VYw_hWvNFtphnl0uWpB9KIvbYi1pvZz4$> >>> 1041 East Butler Road Greenville, South Carolina 29606 >>> CONTACT BY: Phone 1-864-676-5252, Email or MS TEAMS >>> >>> >>> From: Fpdcdesign <[email protected] <mailto:[email protected]>> >>> Sent: Tuesday, June 24, 2025 10:45 AM >>> To: Sprinklerforum <[email protected] >>> <mailto:[email protected]>> >>> Subject: [EXTERNAL] [Sprinklerforum] Backflow turbulence >>> >>> I am working on an untestable fire pump with an “N” shaped RPZ in the >>> suction line. They (just) have the 10X diameter distance on the feed, but >>> the suction pressures are very low (15 psi). It seems that an “N” shaped >>> device would create a lost >>> I am working on an untestable fire pump with an “N” shaped RPZ in the >>> suction line. They (just) have the 10X diameter distance on the feed, but >>> the suction pressures are very low (15 psi). It seems that an “N” shaped >>> device would create a lost more turbulence than a standard straight one. >>> Consequently, should the distance of straight pipe requirement be greater >>> for this arrangement? >>> >>> Todd G Williams, PE >>> Fire Protection Design/Consulting >>> Stonington, CT >>> 860-535-2080 <tel:860-535-2080> (ofc) >>> 860-554-7054 <tel:860-554-7054> (fax) >>> 860-608-4559 <tel:860-608-4559> (cell) >>> >>> >>> NOTICE - This communication may contain confidential and privileged >>> information that is for the sole use of the intended recipient. Any >>> viewing, copying or distribution of, or reliance on this message by >>> unintended recipients is strictly prohibited. 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