Put a gauge on the closest hydrant (or two) and have someone monitor that while you flow the pump. If the gauge on the hydrant stays above 20 psi, then you know that most of the loss is coming between the city main and the fire pump. That could help narrow down your search for partially-closed valves and/or obstructions in the pipe.
-Kyle M @ Aero From: Fpdcdesign <[email protected]> Sent: Wednesday, June 25, 2025 11:53 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: [EXTERNAL] Backflow turbulence The 38 psi is the static pressure from a recent flow test taken at elevation 302. The ground at the entrance to the building is approximately 305. The flow was about 1100 gpm at 28. The backflow is a 6" Febco. The fire pump is a vertical in-line, so my guess is that the maximum rated is about 500 gpm. Even at 150%, the friction loss should only be 3.5 psi, per the literature. They can't get to rated without the suction pressure below 20 psi 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) On Jun 24, 2025 at 12:31 PM, <Mike Morey<mailto:[email protected]>> wrote: What size/model backflow and flow rate? Many N shaped RPZs are up around 15 psi loss when you're running them at the kind of flows a 150% test would see for a given suction size pump. Also the larger units never drop below about a 10 psi loss no matter what. If you're losing that much at or near churn I'd suspect a problem with the backflow itself. Mike Morey 2025 NFSA Top Tech Champion * NICET IV * CFPS Project Estimator * Fire Protection Group Shambaugh & Son, LP an EMCOR Company 7614 Opportunity Drive * Fort Wayne, IN * 46825 direct 260.487.7824 / cell 260.417.0625 email [email protected]<mailto:[email protected]> 24/7<outlook-data-detector://2/> SERVICE LINE 888.217.7055<tel:888.217.7055> [cid:[email protected]] From: Fpdcdesign <[email protected]<mailto:[email protected]>> Sent: Tuesday, June 24, 2025 12:17 PM 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 ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message originated outside your organization. ZjQcmQRYFpfptBannerEnd 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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