In a typical irrigation system that uses a well as the water source, which of the following is NOT a concern as a cause of water hammer?

• A. Trapped air in long pipe runs
• B. Reverse flow when the pump stops
• C. Uncontrolled flow velocity in empty pipes
• D. Valve closure

Answer: (A)

Water hammer happens when a fluid’s velocity changes suddenly, creating a pressure surge that travels through the pipes. In an irrigation system fed by a well, the most direct causes are actions that abruptly stop or drastically accelerate the water flow: closing a valve quickly creates a sudden halt; stopping the pump can cause reverse flow and a negative pressure wave; and filling an empty pipe rapidly with moving water produces a strong transient as the column gains momentum. Trapped air in long pipe runs, on the other hand, tends to cushion the surge because air is compressible and can absorb part of the energy. So it isn’t a primary driver of water hammer, unlike the other factors that actively generate the pressure spike. To reduce hammer effects, use slow-closing valves, keep lines from being left empty, and incorporate air vents, surge tanks, or soft-start pumping practices.