Where is the backflow device? If at the riser and that is 10 feet higher than the test hydrant as you say then the static is correct. 72 psiI less 4.33 psi for elevation equals as close to 67 psi as I can read on a gauge. I also plotted these results and got about 40 psi at 900 gpm. What size orifice are you flowing through? Is it the same as was flowed on the hydrant?
On Mon, Dec 14, 2009 at 8:45 AM, Dewayne Martinez <[email protected]> wrote: > We have a job where the residual pressure recorded during the backflow > test is lower than expected. The hydrant used for the original water > test is about 10ft lower than the system riser and has a flow test > result of 72PSI static, 62PSI residual, flowing 902GPM (off a > circulating system). I had my fitter install a pressure gauge before > the 1st check on the BFP and the we recorded a static of 67PSI but a > residual of 50PSI at a flow of 715GPM. I confirmed with the water > utility that the gate valve for the water lead in is fully open and that > no pumps or valves have been shut off for water main breaks or > maintenance. Unfortunately, they will not run a new flow test in > winter. > Any ideas as to what is causing the low residual pressure? > Thanks, > Dewayne Martinez > Design Build Fire Protection > New Berlin, WI > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > > For Technical Assistance, send an email to: [email protected] > > To Unsubscribe, send an email to:[email protected] > (Put the word unsubscribe in the subject field) > -- Ron Greenman Instructor Fire Protection Engineering Bates Technical College Tacoma, WA Member: SFPE, ASCET, NFPA, AFSA, NFSA AFAA, WSAFM _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
