Which statement correctly defines static pressure and residual pressure on a hydrant?

• A. Static pressure is the pressure when no water is flowing; residual pressure is the pressure under flow.
• B. Static pressure is the pressure under flow; residual pressure is the pressure when no water is flowing.
• C. Static pressure is the pressure when water is flowing; residual pressure is the pressure when no water is flowing.
• D. Static pressure equals residual pressure.

Answer: (A)

Static pressure is the pressure in the hydrant system when the water is at rest and no water is flowing. Residual pressure is the pressure present while water is flowing, after losses from friction, fittings, and elevation have reduced the pressure. This distinction matters because you first assess the system’s potential with static pressure, then verify there is enough pressure to maintain a steady flow during operation by checking residual pressure. The correct statement reflects that static pressure is measured with no flow and residual pressure is measured under flow; the other ideas mix up which state corresponds to each pressure or claim they’re the same, which isn’t accurate.