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 > > > > 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. > How should we address the requirement for a backflow preventer when pump > suction is already low at 150% flow? > > > > Again not a requirement. > > > > 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. > > > > 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 > > > > If testing confirms the standpipe cannot achieve 65 psi at 750 GPM, what is > the recommended course of action? > > How should we address the requirement for a backflow preventer when pump > suction is already low at 150% flow? > > Are there alternative design approaches to meet the water authority’s > requirement while maintaining proper pump operation? > > 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]) > > > > > > > > > > > > > > > > 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. 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