Water hammer is primarily caused by which type of action in the piping system?

• A. Rapidly starting or stopping system flow and valve actions.
• B. Steady flow with no valve movement.
• C. Constant temperature with no pressure changes.
• D. Air leaks only.

Answer: (A)

Water hammer arises from a rapid change in the velocity of the fluid inside a piping system. When a valve is closed quickly or a pump starts or stops abruptly, the moving water has inertia and resists the sudden change, creating a pressure surge that travels as a wave through the pipe. The faster the change, the larger the pressure spike, and the pipe’s stiffness and any air in the line can influence how strong the surge appears.

So the action that generates water hammer is the rapid starting or stopping of system flow and valve actions. Steady flow with no valve movement won’t produce a transient, and while air pockets can affect damping, they aren’t the primary cause.