What causes water hammer, and how is its force calculated?

In pressurized pipes, the phenomenon of significant pressure fluctuations caused by sudden changes in liquid flow velocity. Sudden opening and closing of gates in pipeline systems, sudden shutdown of water pumps in water supply pipelines, operation of the guide vanes of turbines, and turning off faucets in indoor sanitary fixtures can all cause water hammer. Water hammer can cause severe vibrations in pipeline systems, resulting in noise and cavitation. It is the most common factor that causes pipes to rupture. Understanding the variation patterns of water hammer pressure is of great practical significance for the design of water conveyance pipelines and for reducing the destructive effects of water hammer. 　　Ideal water hammer wave process: Consider a water hammer model in which the flow velocity changes suddenly and there is no energy loss during the wave process. The pipe has a length of l, and it is connected to a reservoir upstream. When the valve downstream is suddenly closed, the flow velocity of the liquid near the valve decreases from v to zero, resulting in an increase in pressure. This decelerating and accelerating pressure wave propagates upward at the speed of elastic waves, c, and takes a time of l/c to reach the upstream end; it then propagates downward as a pressure wave whose pressure returns to its original value, taking the same time (l/c) to return to the valve. Thereafter, a decompression wave with pressure lower than the original value propagates upward, and a normal-pressure wave returns to the valve downward. To complete the entire water hammer cycle, a total time of T = 4l/c is required. The aforementioned fluctuation process will continue to repeat in the future. In fact, the valve does not close instantaneously; therefore, the actual fluctuations can be regarded as a sum of a series of small upward waves and small downward waves resulting from the valve closing over a series of short time intervals. During the fluctuation process, viscosity dissipates energy, causing the amplitude of the fluctuations to gradually diminish. 　　Water hammer pressure: The fundamental issue in water hammer is the calculation of the maximum pressure, which generally occurs at the section where the wave is generated (such as at a valve). Based on the aforementioned fluctuation process, a graph of the pressure at the valve over time during ideal water hammer can be drawn. When t = 2l/c, the pressure drops suddenly, due to the reflected wave returning to the valve. In the actual water hammer process, reflected waves still have the effect of altering the pressure at the valve. Therefore, when the valve has not been closed for 2 l/c yet, the flow velocity at the valve continues to decrease while the pressure continues to increase. When the valve is closed for more than 2 l/c, the reflected wave returns to the valve, causing the pressure to drop. Therefore, there are different calculation methods for direct water hammer and indirect water hammer. 　 http://www.hudong.com/wiki/%E6%B0%B4%E5%87%BB http://www.chinabaike.com/article/316/416/2007/20070507109924.html

It seems it can be calculated using Bernoulli’s equation: lol

Pressure change = density of the fluid medium multiplied by change in flow velocity multiplied by sound speed in the fluid medium

Calculating water hammer requires quite extensive theoretical knowledge!