To prevent water hammer, how should you close nozzle, hydrant, valves, and hose clamps?

• A. Slowly
• B. Quickly
• C. In bursts
• D. As needed

Answer: (A)

Preventing water hammer relies on controlling how quickly you stop the flow. When water is moving through hoses and fittings, a sudden shutdown forces that moving water to come to a quick halt. The momentum of the water creates a pressure surge—a shock wave known as water hammer—that can damage pumps, valves, hoses, and fittings. Closing nozzle, hydrant, valves, and hose clamps slowly lets the flow decelerate gradually, spreading the pressure change over a longer period and reducing the peak surge. In practice, ease the nozzle shut, close hydrants and valves a little at a time, and tighten hose clamps gradually. Closing quickly would produce a harmful pressure spike, while bursting or vague “as needed” closures don’t reliably control the rate of deceleration.