What specific action is taken to prevent water hammer in a long pipeline carrying liquid, and why does it work?

The most common and effective action to prevent water hammer in a long pipeline carrying liquid is to implement slow-closing valves, or to control the valve closure rate. Water hammer is a pressure surge or wave that occurs when a fluid in motion is forced to stop or change direction suddenly. This sudden change in momentum creates a pressure wave that propagates through the pipeline, potentially causing significant damage to the pipe, valves, and other equipment. Fast valve closure is a primary cause of water hammer because it abruptly stops the flow of liquid. Slow-closing valves, or controlled valve closure rates, mitigate water hammer by gradually decelerating the fluid. This gradual deceleration reduces the magnitude of the pressure surge. For example, instead of closing a valve in one second, a slow-closing valve might take 30 seconds or more to fully close. The slower closure allows the kinetic energy of the fluid to dissipate gradually, preventing the sudden pressure spike. Other methods, such as installing surge tanks or air chambers, can also help absorb pressure surges, but controlling the valve closure rate is typically the most effective and practical approach for preventing water hammer. These devices act as accumulators to dampen the pressure waves, but are often costlier and require more space than simply using appropriately specified valves or actuators with controlled closure rates.