Thank you all for the detailed responses and recommendations, I really appreciate the time and expertise here.
Our next step will be to perform a hydrant flow test during peak municipal demand hours, along with a fire pump flow test and standpipe calculation / flow test to fully understand the water supply and actual system demand. I’ll return to this thread and share the final test results, backflow and fitting pressure loss, and the final outcome. Thanks again! 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. From: [email protected] <[email protected]> Sent: Friday, March 6, 2026 1:17 PM To: 'Discussion list on issues relating to automatic fire sprinklers' <[email protected]> Subject: [Sprinklerforum] Re: Backflow Preventer on Fire Pump Suction Brett, You’re getting great feedback and very accurate technical answers to your situation, but I want to weigh in with a practical approach contribution… First, they say the “Golden Rule” is, “he who has the gold, makes the rules.” In your case, the water is the gold, and the water authority makes the rules. NFPA 20 recommends installing the backflow preventer on the discharge side of the pump, but water districts typically require it on the suction side. Todd’s point about getting a new flow test is spot on, because while you’re adding the fixed loss from the backflow, you may also have a different water supply than the one available when the system was initially built. (city supply plus fire pump output = total supply) If the current water supply plus fire pump production can meet the demand for the fire sprinklers at the highest level, I would consider discussing the matter with your fire marshal to determine whether they would accept the system as installed and with the new backflow. Standpipes are for first responders (only), and they show up with their own fire pump. The pressure needed at the nozzle depends heavily on the equipment used by any fire department, so the 65 psi original design criteria may not even deliver the pressure they currently want, not to mention the nearly 30 psi loss over 100 ft of 1-1/2 fire hose (appliance loss). Your data show you have 110 psi at 100% flow, and you need 56.29 psi just for elevation, assuming the pump is on the ground floor. If the system demand is at the top level, and the demand is 68 psi, the standpipe demand isn’t the biggest problem. Lastly, most existing fire pump rooms are not large enough to meet the 10-pipe-diameter distance from the suction flange rule, so it is very important to purchase a backflow preventer with OS&Y gate valves, NOT butterfly-type valves, which would be tempting for space-saving concerns, but are not permitted in suction piping. There are many reasons fire pump production can degrade over time, but, as Todd noted, I’d look at the incoming water supply first. Just sharing a few Friday afternoon thoughts [https://www.dropbox.com/s/g4h8r7hdtsr6154/AFSA_L.png?raw=1] Bob Caputo, CFPS President American Fire Sprinkler Association 1410 E Renner Rd., Suite 150 Richardson, TX 75082 c: 760-908-7753 p: 214-349-5965 ext124 w: firesprinkler.org<http://firesprinkler.org/> New Year, New Training! Learn design, hydraulic calculations, and ITM with AFSA’s best-in-class training! Click here<https://firesprinkler.org/education-training/> to learn more and register now for Beginning Design School, Sprinkler Hydraulics Calculations Course, NFPA 25 Essentials Workshop, and Advanced Hydraulics Calculations Course. From: Fpdcdesign <[email protected]<mailto:[email protected]>> Sent: Friday, March 6, 2026 10:24 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]<mailto:[email protected]>> Subject: [Sprinklerforum] Re: Backflow Preventer on Fire Pump Suction Brett, here is Todd’s take (having seen a lot of pumps with issues lately): 1. Make sure you have the 10X pipe diameter distance between the backflow preventer and the pump suction. 2. Based on the pump test, you have a 750 gpm pump rated at 70 psi and producing only 65 psi at 750 gpm during the test. 63 psi would be a failed test. How does that compare with previous tests? It could be an issue with the pump or the suction piping. It is a 51 year old pump. Needs investigating. 3. You need to get a hydrant flow test. I wouldn’t touch a pump project without one. 4. You need to do a standpipe calculation to see what your demand is at the pump discharge. 5. Don’t draw the public supply below 20 psi during a test. 6. There is a section in NFPA 25 that states that if a pump cannot be tested to 150%, but it can be tested to the greater of system demand or rated flow, then it can be considered acceptable. 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 Mar 6, 2026 at 10:52 AM, <Chris Dorn<mailto:[email protected]>> wrote: 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]<mailto:[email protected]>> Sent: Friday, March 6, 2026 9:55 AM To: [email protected]<mailto:[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. _________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]<mailto:[email protected]>
_________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]
