Which phenomenon results from a sudden stoppage of water flow?

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

Answer: (C)

When a stream of water is moving and the flow is suddenly stopped, the moving water wants to keep going. That momentum creates a pressure wave that travels through the piping, causing a sudden spike in pressure—this is water hammer. In fire operations, it can happen if a valve is slammed shut or a nozzle is closed quickly, or if the pump is stopped abruptly, and it can lead to banging in hoses or damage to fittings if the surge is large. To prevent it, close valves smoothly and gradually and follow proper pump discharge procedures. Hydrant hammer and nozzle hammer describe the surge as it appears at specific components, but the underlying phenomenon is water hammer. Internal pressure refers to the normal or static pressure in the system, not the sudden transient surge.