Fire Hydrant Flow Calculator 
Fire Hydrant Flow Test Analysis. Calculate hydrant residual flow, pressures 

Register to enable "Calculate" button in fire hydrant flow test calculator. Plan View of Portion of Pipe System Containing Fire Hydrants and Photo of a Hydrant in Athens, Ohio
Fire Hydrant Flow Calculator Equation (AWWA, 2006, p. 52) Fire Hydrant Flow and Pressure Tests After conducting the fire hydrant test, the fire hydrant flow calculator can be used to determine the flow rate Q_{d} at the desired pressure P_{d}. The fire hydrant flow calculator uses the equation shown above. The desired pressure P_{d} is typically 20 psi. For instance, if the static pressure P_{s} was measured as 68 psi, the residual pressure P_{r} was measured as 43 psi, and the flow Q_{r} at the residual pressure was measured as 1710 gpm, then the flow Q_{d} at the desired pressure of 20 psi is 2432 gpm using the calculator. The flow rate Q_{d} of 2432 gpm is higher than the measured value Q_{r} of 1710 gpm. If a fire hose with a pump is connected to hydrant #1 and the pump turned on drawing water out of the hydrant, the effect of drawing water out of the hydrant will cause the pressure at hydrant #2 to drop. If the pressure in hydrant #2 drops to P_{d} of 20 psi, then the expected flow rate out of hydrant #1 is Q_{d} of 2432 gpm. The computation of the desired flow Q_{d} is based on the equation above which is the most commonly used equation for fire hydrant flow test analysis. The equation has a coefficient of 0.54 which is based on the HazenWilliams equation (see HazenWilliams Equation or HazenWilliams Design Calculator). The HazenWilliams equation is widely used to analyze municipal water flow in pressurized pipes. For modeling pressurized pipe flow, the HazenWilliams equation includes pipe diameter, pipe length, and a pipe roughness coefficient. None of those parameters are in the fire hydrant test equation. Since the fire hydrant equation does not include those parameters, the results of a particular hydrant test cannot be expected to necessarily predict test results of other hydrants. Also, since other factors impact performance of the pipe system, tests at other times or other days will likely yield different measured values for P_{s}, P_{r}, and Q_{r}. Homes, businesses, industries, and other water users have different water demands on the piping system from one day to another and from time to time within a day. Also, a water system may get expanded, pipes may get cleaned, or pipes may get calcified. In addition to computing the flow rate Q_{r} at desired pressure P_{r}, you can solve for any of the five parameters by selection from the dropdown menu in the calculator. Fire Hydrant Flow Calculator Units Error Messages given by fire hydrant flow calculator References American Water Works Association [AWWA]. (2006). Installation, field testing, and maintenance of fire hydrants. Manual of Water Supply Practices. M17. 4th edition.
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