What is the difference between static and residual hydrant pressure?

• A. Static Pressure Is When Water Is Not Moving; Residual Pressure Is The Pressure During Water Flow
• B. Static Pressure Is During Flow; Residual Is When Water Is Not Moving
• C. Static Pressure Is After Operation; Residual Is During Hose Test
• D. They Are The Same

Answer: (A)

Static hydrant pressure is the pressure in the water system when no water is moving—when taps are closed and nothing is flowing. Residual hydrant pressure is the pressure you read while water is flowing from the hydrant, after you’ve opened the valve and started drawing water through hose lines. Because water moving through pipes experiences friction and elevation losses, the pressure drops from the static value, so residual pressure is usually lower and tells firefighters whether the system can sustain a needed flow. The other descriptions mix up the states—static during flow or residual when water isn’t moving aren’t accurate—so this definition best captures the difference.