Which statement best describes surge or water hammer in piping?

• A. A continuous low pressure
• B. A type of valve
• C. A method to increase flow
• D. A rapid pressure rise due to sudden valve closure or changes in flow

Answer: (D)

Surge or water hammer is a transient hydraulic phenomenon caused by the inertia of moving water. When flow is interrupted suddenly—such as a valve closing quickly or a pump stopping—the moving water can’t stop instantaneously. It pushes against the rest of the system, sending a pressure wave that travels through the pipes and creates a rapid, temporary spike in pressure. That rapid pressure rise is exactly what water hammer describes, and it can be enough to damage pipes, fittings, and valves if not controlled.

This is not about a continuous low pressure, it isn’t a valve itself, and it isn’t a method to increase flow. It’s the sudden, momentary pressure surge that results from abrupt changes in flow.