Basic Firefighter Written Practice Exam

What is the most likely cause of water hammer?

1. Closing the nozzle quickly

2. Opening the nozzle

3. Increasing water pressure

4. Low water temperature

The correct answer is: Closing the nozzle quickly

Water hammer is a pressure surge or wave that occurs when a fluid in motion is forced to stop or change direction suddenly. The most common scenario that leads to water hammer is when a nozzle is closed quickly, which causes the moving water to abruptly decelerate. This sudden stop creates a pressure wave that travels back through the piping system, resulting in the characteristic banging or hammering noise. Closing the nozzle quickly disrupts the normal flow of water, generating a considerable change in momentum. This disruption can create shockwaves that propagate through the water and pipe system, manifesting as water hammer. Understanding this phenomenon is crucial for firefighters and those working with high-pressure water systems to prevent potential damage to equipment and ensure safety. The other options provided do not typically lead to water hammer. Opening a nozzle would not cause a sudden change in flow direction or speed, and increasing water pressure itself does not inherently lead to water hammer unless there is a sudden closure or obstruction. Low water temperature is also unrelated to the dynamics that cause water hammer, as it focuses more on fluid properties rather than flow behavior.