Firefighting agencies can use water data from hydrant flow tests for training, planning, and marking hydrants. Municipalities also use these data for system planning and design, as well as for the calibration of hydraulic models.
When performing a hydrant flow test, ensure the water flows freely and that at least one alarm device is functioning. That can be a water motor gong or an electrical switch.
Static Pressure
A static pressure gauge is attached to a test hydrant in fire flow testing. It will measure the static water pressure at that hydrant, which measures the normal operating pressure in a water main under distribution-system flow conditions.
The static pressure at the hydrant is a good indicator of how much pressure there will be when flowing a hose line through the hydrant, which will determine the flow rate that the hose line can produce. Friction loss, the resistance that occurs when water moves along the inside wall of a hose, hose line, pipe, or mains, also affects the flow rate.
Static pressure of 30 psi is required to achieve accredited fire hydrant performance. Still, in areas with low pressure, NFPA allows calculations based on residual pressures, which are half the static pressure. This allows a hydrant with a static pressure of 30 psi to be calculated on the basis that pulls the hydrant down to 15 psi, improving its accredited performance.
Residual Pressure
Fire hydrant residual pressure is important when performing a hydrant flow test. It accounts for the water main’s capacity to produce a water flow rate higher or lower than the hydrant’s static and pitot pressures.
Residual pressure is measured in a flow test by taking static and residual pressure readings on a hand-held pitot pressure gauge. Both readings are then recorded at a static/residual hydrant between the flow hydrants and the water supply.
Once you’ve taken the static and pitot pressure readings on the hydrants, you can close the flow hydrant slowly. This will help you get an accurate result.
Pitot Pressure
A pitot pressure gauge is a hand-held device that measures the velocity pressure of a stream of water. These are commonly used in hydrant and pump flow testing.
For a hand-held pitot, choose a unit attached to the test hydrant, hose, or nozzle for quick and easy readings. The unit should be capable of measuring static and residual pressure.
Fire departments and city planners use hydrant flow testing information to design water-based fire protection systems.
Flow Rate
Water flow tests verify the pressure and flow available at fire hydrants in a city’s water distribution system. This information is important for various purposes, including fire protection, assessing sprinkler system design, and hydrant marking.
Performing fire flow tests regularly can detect potential issues in a hydrant’s piping, valves, and connections to the main. These include closed valves, heavy pipe-wall deposits, and other problems that may reduce the water supply’s capacity to fight fires.
The process involves using a pitot gauge and measuring static (non-flowing), residual pressure, and water discharge rate in gallons per minute. This information can then be used to calculate available fire flow.
Many water utilities do not have workflows specifically for hydrant flow testing, so they develop workarounds to handle this process. These workarounds often lead to data silos and inefficient reporting.
