What causes water hammer in a plumbing system?

Water hammer occurs when there is an abrupt shut-off of high-velocity water flow in a plumbing system. This phenomenon happens because the sudden stop causes the kinetic energy of the moving water to create a high-pressure wave or shockwave. When water is flowing at a high velocity and it suddenly changes direction or comes to a halt—often due to a valve closing swiftly—the sudden deceleration leads to a rapid increase in pressure.

This pressure surge can cause pipes to vibrate and make a loud banging noise, which is characterized as a "hammer" effect. If this water hammer is not managed, it can lead to potential damage in the plumbing system, including loosening pipe fittings and causing leaks.

In contrast, a gradual increase in water pressure does not create the kind of shockwaves associated with water hammer. The absence of surge tanks may contribute to pressure fluctuations, but it is not the direct cause of the hammer effect. Similarly, low water pressure in the system generally does not lead to the violent shockwaves that define water hammer incidents.