What action should be taken when opening and closing system valves to prevent water hammer?

• A. Open and close system valves slowly.
• B. Open and close system valves rapidly.
• C. Leave valves untouched during operation.
• D. Operate valves to start and stop quickly.

Answer: (A)

Water hammer happens when flow velocity in a pipe changes suddenly. If a valve is opened or closed quickly, the moving water can’t instantaneously adjust to the new flow rate, creating a pressure surge that can damage pipes, fittings, and pumps. Opening and closing slowly lets the flow rate and pressure change gradually, minimizing those transient pressures. In practice, start with the valve almost closed and advance it slowly to the desired setting, then back off slowly when stopping. This throttling approach reduces shock compared with rapid movements, which produce large pressure spikes; simply leaving valves unmoved or moving them quickly would not protect the system from water hammer.