It is an ongoing dilemma in Phoenix. The water dept. does the flow test and does not apply NFPA #291. After all they are the water dept. So the water dept. sends out a flow test graph based on a .9 C for the butt and does not apply the other, usually .83 for pitot pressure over 8 psi (I think). Now we have an official city flow test that is not reduced IAW NFPA #291. The official test usually gets submitted with the fire flow calc's to Development Services, not the fire dept., and is subsequently approved. If we submit the 4" flow test to the fire dept. with the sprinkler calc's we take the added reduction. Phx only allow a 50% reduction to Appendix B so we try to get flow tests in the neighborhood of 4000 gpm when calculating fire flow.
Because of the uncertainty of a 4" flow test we now try to use multiple 2.5" outlets with hose monsters or plain pitots so we don't have to deal with the added reduction. Ron Fletcher Aero Automatic Sprinkler 21605 N. Central Ave Phoenix, AZ 85024 P: 623.580.7836 F: 623.434.3420 C: 602.763.4160 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Travis Mack, SET Sent: Thursday, February 12, 2009 10:09 AM To: [email protected] Subject: flow tests using pumper connections How many of my colleagues out there apply the requirements of NFPA 291 when calculating the flow tests done with a pumper connection, instead of the 2½" outlet? I was taught that when using the 4", 4½" or 5", whatever your hydrant is, you have to add another coefficient. Reference is 4.8.2 For pumper outlets, the approximate discharge can be computed from Equation 4.7.3 using the pitot pressure (velocity head) at the center of the stream and multiplying the result by one of the coefficients in Table 4.8.2, depending upon the pitot pressure (velocity head). (I can't paste the table and get it to format properly) 4.8.3 These coefficients are applied in addition to the coefficient in Equation 4.7.3 and are for average-type hydrants. 4.7.3 is the standard equation: Q=29.83*c*d^2*p^.5 I have received a lot more flow tests from local water and fire departments where this modification is not being used. The funny thing is that when I try to use this modification, the authority does not want to accept my calculations because my flow is not what was provided. I have just been doing the calcs with the proper flows initially to get my sizes, then I just put in the flow test provided and show a bigger safety margin. This really only comes into play on large demand systems, such as storage. It is not an issue on most LH and OH systems. Have I been wrong all of these years, or are the local authorities I am dealing with not up to date on the calculation method? Travis _______________________________________________ Sprinklerforum mailing list http://lists.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 http://lists.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)
