Questions 1. If testing confirms the standpipe cannot achieve 65 psi at 750 GPM, what is the recommended course of action? Install a higher pressure fire pump. 150% is not a requirement. 65psi definitely is though. Fire pumps make pressure, not water. 2. How should we address the requirement for a backflow preventer when pump suction is already low at 150% flow? Again not a requirement.
1. Are there alternative design approaches to meet the water authority’s requirement while maintaining proper pump operation? The water purveyor is protecting their system from a backflow situation. They are not going to let this go. 1. Water authority wants the backflow detector assembly on the suction side of the pump. Find the lowest pressure loss backflow device and go with it. Just my opinion. Chris From: Brett Barrall <[email protected]> Sent: Friday, March 6, 2026 9:55 AM To: [email protected] Subject: [Sprinklerforum] Backflow Preventer on Fire Pump Suction Hello! This is my first time posting, I’ll try to keep it short. We have a project with a new customer where the water authority is requiring a backflow preventer on the suction side of an existing fire pump. We want to confirm the proper approach due to potential hydraulic concerns. * Building height: 130 ft * System type: Wet pipe sprinkler and standpipe * Stair Tower 1: Class III combined automatic standpipe * Stair Tower 2: Automatic Class III standpipe * Standpipe flow requirements - 65 psi at 750 gpm (System installed 1975) * Fire pump: 70 psi at 750 GPM, city main supply * Hydrant flow test not performed, assuming static pressure at street around 75 psi. * No standpipe flow information. I recommended a standpipe flow test to be performed for documentation purposes. Existing Suction Piping * 4” × 6” concentric reducer at pump suction flange, recommended replacement with 4” × 6” eccentric reducer * 1975 water meter to be removed during backflow installation. Couldn’t find data sheets on this water meter to determine friction loss at system demand. Pump Test Data Flow Suction Pressure Discharge Pressure Churn 75 psi 155 psi 100% (750 GPM) 45 psi 110 psi 150% (1125 GPM) 5 psi 50 psi Sprinkler system demand: 268 GPM at 68 psi * Light Hazard * Apartments Concern * At 150% flow, suction is already 5 psi without a backflow preventer. * Adding a backflow preventer with additional fittings will introduce friction loss and will pull city main below zero during high demand. * Preliminary calculations indicate the standpipe may not achieve 65 psi residual at 750 GPM; (System installed 1975), verification pending a standpipe flow test. Questions 1. If testing confirms the standpipe cannot achieve 65 psi at 750 GPM, what is the recommended course of action? 2. How should we address the requirement for a backflow preventer when pump suction is already low at 150% flow? 3. Are there alternative design approaches to meet the water authority’s requirement while maintaining proper pump operation? 4. Water authority wants the backflow detector assembly on the suction side of the pump. Thank you for any guidance. Thank You, Brett Barrall Fire Sprinkler Designer [email protected]<mailto:[email protected]> [image004.jpg@01D445D6] 50 S. Museum Road, Reading, PA 19607<https://goo.gl/maps/A3D5Y6oTJUT2> Office: 610-775-1200 ● Toll Free: 1-800-344-4012 www.bsgi.com<https://www.berkshiresgi.com/> Satellite Offices in York & State College ● PA State Contract & Costars Participating Vendor ● ----- Email Disclaimer ----- This email and any files transmitted with it are confidential and are intended for the named recipient(s). If you are not the intended recipient, you are hereby notified that you have received this communication in error and that any copying, disclosure, dissemination, distribution or review of it or its contents is prohibited. If you have received this email in error, please notify the sender and immediately delete this email from your system.
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