Which of the following can cause "water hammer"?

"Water hammer" is a phenomenon that occurs in piping systems when there is a sudden change in water flow, typically caused by the rapid closing of a valve. This sudden stop causes a pressure wave that travels through the pipe, leading to a loud banging noise and potential damage to the system.

When valves are closed quickly, the momentum of the moving water is abruptly halted. This creates high-pressure fluctuations in the system and can result in vibrations and a "hammering" sound. These effects can lead to physical issues in pipes, fittings, and valves if not managed properly.

In contrast, slowly opening valves allows water to adjust to the change in flow more gradually, reducing the risk of a pressure surge that contributes to water hammer. Constant water flow and low water pressure do not typically induce the kind of rapid pressure changes that lead to this phenomenon.