Which instrument is used to measure hydrant flow in the example?

Which instrument is used to measure hydrant flow in the example?

• A. Pitot gauge
• B. Flow meter
• C. Pressure gauge
• D. Anemometer

Answer: (A)

Measuring hydrant flow relies on capturing the speed of water in the hydrant discharge to calculate how much water is flowing. A Pitot gauge uses a Pitot tube to measure velocity pressure in the moving water—the difference between stagnation pressure and static pressure. That dynamic pressure directly relates to water velocity, via v ≈ sqrt(2ΔP/ρ). Once you know the velocity and the discharge area, you can compute flow as Q = v × area. This method is practical for hydrant tests because it provides a direct read of velocity in the flowing water and lets you derive flow without needing a bulky inline meter. A pressure gauge only reads static pressure, not velocity, so it can’t determine flow. An anemometer measures air flow and isn’t suitable for water in hydrants. A flow meter could measure flow, but the Pitot approach is the standard method for hydrant flow testing because it yields velocity directly in the discharge stream.

Measuring hydrant flow relies on capturing the speed of water in the hydrant discharge to calculate how much water is flowing. A Pitot gauge uses a Pitot tube to measure velocity pressure in the moving water—the difference between stagnation pressure and static pressure. That dynamic pressure directly relates to water velocity, via v ≈ sqrt(2ΔP/ρ). Once you know the velocity and the discharge area, you can compute flow as Q = v × area. This method is practical for hydrant tests because it provides a direct read of velocity in the flowing water and lets you derive flow without needing a bulky inline meter. A pressure gauge only reads static pressure, not velocity, so it can’t determine flow. An anemometer measures air flow and isn’t suitable for water in hydrants. A flow meter could measure flow, but the Pitot approach is the standard method for hydrant flow testing because it yields velocity directly in the discharge stream.