What is the best definition of water hammer?

Water hammer is best defined as the sudden surge of pressure that occurs when a fluid in motion is forced to stop or change direction abruptly. This phenomenon typically happens when a valve is closed quickly, leading to a dramatic increase in pressure within the piping system. The rapid change can produce a loud banging noise, hence the term "water hammer." This surge can cause damage to pipes and fittings if not managed properly.

Understanding water hammer is crucial for fire fighters and those involved in maintaining water systems as it helps them recognize the potential risks associated with pressure surges and implement preventive measures accordingly. The other definitions do not accurately describe this specific hydraulic event; a leaking pipe causes pressure loss rather than a surge, while a gradual increase of pressure is not related to the immediate and explosive nature of water hammer. A constant flow of water does not involve any abrupt changes, thereby eliminating it from being a definition of water hammer.