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]
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