Which valve, if closed too fast, would cause serious water hammer compared to the others listed?

• A. Gate valve
• B. Butterfly valve
• C. Ball valve
• D. Check valve

Answer: (B)

When water is flowing and a valve shuts abruptly, the moving water can’t adjust, creating a pressure surge known as water hammer. A butterfly valve can close very quickly with a simple quarter-turn motion, which can snap the flow to a stop in an instant. That abrupt closure causes a large, fast-decaying change in momentum of the water, producing a strong transient pressure spike in the system. Other valves in this list are generally operated more slowly or have designs that don’t close as abruptly, so they’re less likely to generate as severe a hammer when closed quickly. To minimize risk, closures should be performed gradually or with devices designed to dampen the surge.