Thanks, I am going to have a meeting with the inspector and water department to try and come up with a resolution to the issue. Thanks for everyone's input, as always, invaluable. Dewayne
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of J. Scott Mitchell Sent: Monday, December 14, 2009 10:52 PM To: [email protected] Subject: Re: forward flow test problem You can start whittling away at this with things you know or can determine fairly easily. Right not you're seeing a 15 psi differential at 715 gpm. A little less than 5 psi of that is attributed to elevation. There's a certain amount of the remaining 10 psi that is attributed to the friction in the pipe between the 2007 test hydrant and the gauge you installed before the backflow preventer. Probably not much, but you can calculate it and subtract it. Now, whatever you have left goes into the think tank. In two years anything could have happened. The water department could have taken segments offline thus reducing the number of flow paths. There could be valves partially closed at critical junctures in the grid thus restricting flow paths. The water department could have had the pumps set to start at a different pressure in 2007 than they do now. They could have the supplemental pumps turned off altogether since in the winter they may have sufficient elevation in the tanks to meet the demands. The water department could have installed some PVC imported from China with a new microbe that corrodes plastic. I would probably rule out high demanding neighbors since this would be reflected in a drop in "static" pressure that is really never static as mentioned in another post. J. Scott Mitchell, P.E. --- On Mon, 12/14/09, Dewayne Martinez <[email protected]> wrote: From: Dewayne Martinez <[email protected]> Subject: forward flow test problem To: [email protected] Date: Monday, December 14, 2009, 10:45 AM 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) _______________________________________________ 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) _______________________________________________ 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)
