Which statement about water hammer prevention is true?

Which statement about water hammer prevention is true?

• A. Opening valves slowly and venting properly help prevent water hammer.
• B. Water hammer cannot be prevented under any circumstances.
• C. Only large systems experience water hammer.
• D. Water hammer is desirable to mimic system startup.

Answer: (A)

Water hammer comes from a rapid change in fluid velocity in a confined piping system, which creates a pressure surge. The speed at which the flow is started or stopped determines how big that surge can be. Opening valves slowly slows the rate of velocity change, so the momentum change ΔV is smaller and the resulting pressure rise is reduced. Venting properly helps keep the pipe fully wetted and free of trapped air or vapor pockets; when air pockets are present, they compress and can amplify or unpredictable the transient when flow changes, leading to higher or erratic pressure spikes. Together, these practices directly limit the conditions that generate water hammer, reducing risk of damage during operation and startup. The other statements miss the fact that proper operation can prevent many surges, that even small systems can experience water hammer, and that the phenomenon is not something to be desired during startup.

Water hammer comes from a rapid change in fluid velocity in a confined piping system, which creates a pressure surge. The speed at which the flow is started or stopped determines how big that surge can be. Opening valves slowly slows the rate of velocity change, so the momentum change ΔV is smaller and the resulting pressure rise is reduced. Venting properly helps keep the pipe fully wetted and free of trapped air or vapor pockets; when air pockets are present, they compress and can amplify or unpredictable the transient when flow changes, leading to higher or erratic pressure spikes. Together, these practices directly limit the conditions that generate water hammer, reducing risk of damage during operation and startup. The other statements miss the fact that proper operation can prevent many surges, that even small systems can experience water hammer, and that the phenomenon is not something to be desired during startup.