hi. i am little bit confused about fire hydrant testing.
what is the criteria to select the number of hydrants to flow during testing.
as per AHJ, the minimum acceptable residual pressure is 50 psi.
Please see NFPA 291 Chapter 4, Flow Testing.
4.1.1 For the purpose of uniform marking of fire hydrants, the ratings should be based on a residual pressure of 20 psi(1.4 bar) for all hydrants having a static pressure in excess of 40 psi (2.8 bar). <<The AHJ can of course set a higher pressure.>>
4.3.7 If the mains are small and the system weak, only one or two hydrants need to be flowed.4.3.8 If, on the other hand, the mains are large and the system strong, it may be necessary to flow as many as seven or eight hydrants.
Thanks for the reply. how do we come to a conclusion that a main is small and weak or large and strong??
NFPA 291 4.3.6
"To obtain satisfactory test results of theoretical calculation of expected flows or rated capacities, sufficient discharge should be achieved to cause a drop in pressure at the residual hydrant of at least 25%..."
4.6.6 "pitot readings of less than 10 psi and more than 30 psi should be avoided, if possible"
Flow enough water to get a 25% drop is pressure from static to residual readings. If one hydrant/opening is does not cause enough drop, continue opening and taking readings at other hydrants/openings until you achieve 25% pressure drop.
Thanks for the reply.
Check your design, what is in it. Hose allowance that is for example 100gpm (inside) and 400gpm (outside). You basicly need as many hoses to fulfill 100 gpm inside and 400 gpm outside. Hope I helped a bit
Thanks Michael. I am guessing that your statement is based on highlighted part in NFPA clause "4.3.6 - To obtain satisfactory test results of theoretical calculation of expected flows or rated capacities, sufficient discharge should be achieved to cause a drop in pressure at the residual hydrant of at least 25 percent, or to flow the total demand necessary for fire-fighting purposes".
yes NFPA 291 4.3.6
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