Whether in quiet residential neighborhoods or large commercial areas, firefighting operations rely on having the right amount of water to do their jobs. Flow testing is essential to verify that the water system works as it should.
The information collected through hydrant flow tests is also helpful in designing water systems for municipal and privately owned buildings.
Hydrant Capacity
Fire hydrant flow testing determines the rate of water available from fire hydrants for use in an emergency. It also uncovers several mechanical problems, including closed valves, heavy pipe-wall deposits, and other infrastructure issues that can reduce hydrant flow rates.
The tests involve using two formulas that require gathering critical data from a residual hydrant’s static and residual pressure readings, the inside diameter of the hydrant’s nozzle, and a few other measurements. This data is used in two sequential formulas that calculate the hydrant’s actual flow (gallons per minute) and predicted flow at the desired residual pressure of 20 psi. A hydrant’s available fire flow is then determined by adding the gallons per minute from each flow.
Hydrant Spacing
Fire flow testing provides critical information, including firefighter training, planning and marking hydrants, water system design, and mainline sizing. Accurate data helps ensure that firefighting agencies have enough water for the community’s needs and can help with sprinkler system design for commercial or residential structures.
When conducting a fire hydrant flow test, the procedure requires identifying a static/residual hydrant and a flow hydrant. The static pressure is the pressure under normal distribution system conditions, and the residual pressure is measured at the hydrant when no water is flowing. This is measured at the same time as the flow readings are taken. The difference in static and residual pressures determines the hydrant capacity.
Hydrant Pressure
Fire hydrant flow tests ensure that firefighting hose lines have the necessary water pressure to combat a residential structure fire. Fire hydrant flow test results allow firefighters to plan for the water requirements of firefighting operations and identify issues such as blockages or infrastructure problems that may affect their performance.
To conduct a fire hydrant flow test, a tester collects vital information such as the hydrant’s static and residual pressure, discharge coefficient, and more. These data points are then used to run two sequential formulas: the hydrant’s available fire flow in gallons per minute (gpm) and its predicted flow at the desired residual pressure in gpm.
NFPA recommends performing flow tests during periods of peak demand to simulate conditions during a fire best. Street pressures tend to be lower in the morning and higher later in the day, which helps to reflect a typical emergency accurately. After testing, the fire department slowly closes the hydrant.
Hydrant Maintenance
All fire hydrants must be in good condition to ensure they function correctly when called on in an emergency. Hydrant flow tests help to uncover mechanical problems such as leaking valves, plugged drain holes, and incorrect nozzle/pumper sizes. These issues can be costly if they are not addressed in time for the fire hydrant to be used.
During the hydrant flow test, the hydrant tester gathers critical information, including PSI readings from the static and residual hydrants, water main capacity, determination of discharge, and calculation results. This information is then entered into two sequential formulas to predict a fire hydrant’s available fire flow.
After recording the pressure at the hydrant in question, it is essential to take a second static pressure reading and compare it to the first. If this reading drops significantly, it could indicate a water main break that occurred while the hydrant was being tested and needs to be corrected.
