Water Hammer in Pipes – Cause of Pressure Surge Statement: Water hammer occurs in pipelines due to a sudden change in the velocity of the flowing liquid (for example, rapid valve closure or pump trip).

Introduction:
The question explores the physical cause of water hammer, a transient pressure surge that can damage pipes and fittings. Understanding its origin helps in designing protective measures such as surge tanks and slow-closing valves.

Given Data / Assumptions:

• Pressurized pipe conveying a liquid (commonly water).
• Abrupt change in flow velocity imposed by system operation.
• Finite wave speed due to fluid compressibility and pipe wall elasticity.

Concept / Approach:

Sudden velocity changes create compression or expansion waves that travel at the elastic wave speed. The classic Joukowsky equation estimates the surge magnitude based on the instantaneous change in velocity.

Step-by-Step Solution:

Verification / Alternative check:

Field observations show peak pressures immediately after quick valve closures; measurements agree with Joukowsky predictions for many systems.

Why Other Options Are Wrong:

Disagree: Ignores the fundamental mechanism. Occurs only due to temperature change: Thermal effects cause expansion but are not the classic water-hammer trigger. Occurs only in open channels: Water hammer is characteristic of pressurized conduits.

Common Pitfalls:

Assuming incompressibility eliminates water hammer; neglecting pipe wall elasticity; ignoring air pockets that can cushion or complicate transients.

Final Answer:

Agree