A sudden stoppage of water flow through a hose or pipe is known as water hammer.

• A. Water hammer
• B. Internal pressure
• C. Nozzle hammer
• D. Hydrant hammer

Answer: (A)

When water in a hose or pipe is moving and the flow stops suddenly, the moving water has momentum and tries to continue flowing. That momentum can’t stop instantly, so it creates a rapid rise in pressure inside the pipe—a hydraulic shock called water hammer. This surge travels through the system, can bang fittings, and even damage pipes if the flow is stopped abruptly. In firefighting, this is why we’re careful to close valves and nozzles smoothly rather than snapping them shut; it helps limit the pressure spike.

The term that describes this phenomenon is water hammer. The other phrases aren’t standard terms for this surge in pressure, and they don’t capture the sudden pressure spike caused by stopping flow.