water hammer effect

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Water hammer is also known as hydraulic shock. It refers to the phenomenon that during the transfer of water or other liquids, sudden changes in flow velocity and significant fluctuations in pressure occur due to reasons such as the sudden opening and closing of valves or the abrupt start-up and shutdown of water pumps. Due to the inertia of the pressurized water flow, shock waves are generated, and the impact of the water column on the pipes is what is known as water hammer. 　　Due to the inertia of the water flow against the inner wall of a smooth pipe, the hydraulic pressure reaches its maximum value very quickly; this can lead to damage such as damage to valves and pump components. This is what is known in hydraulics as the \"water hammer effect\", or positive water hammer ； Conversely, the sudden opening of a valve or water pump can also generate a water hammer effect, known as negative water hammer. Such pressure shock waves caused by severe fluctuations can easily lead to pipe rupture due to localized overpressure and equipment damage. Therefore, protection against water hammer effect is a key factor that must be considered in the design and construction of fluid pipeline engineering. 　　Conditions for the occurrence of water hammer: 1. Sudden opening or closing of valves; 2. Sudden shutdown or startup of pump units; 3. Transporting liquid upward through a single pipe (with a height difference in the water supply system exceeding 20 meters); 4. High total head (or operating pressure) of the pump; 5. Excessively high flow velocity of the fluid in the pipelines; 6. Long pipelines with significant changes in terrain. 　　7. Irregular construction poses hidden risks to pipeline projects. 　　According to the principles of hydraulics, on pipe racks and hills with significant undulations, at the highest points of the pipes, exhaust valves should be designed and installed. During transportation, gas within the pipeline escapes and accumulates in the raised areas of the pipeline, which can even lead to air blocks. When the flow rate of the medium in the pipeline fluctuates, the air bubbles formed in these raised areas keep compressing and expanding. The pressure generated by the compression of gas is dozens or even hundreds of times greater than that resulting from the compression of the medium itself. In such cases, pipelines with such issues may experience the following problems: (1) No fluid is observed downstream after the medium is pumped into the pipeline upstream, as the air bubbles inside the pipeline block the flow of water, causing a separation of the liquid column. 　　⑵The compressed gas inside the pipe, when compressed to its maximum limit, expands rapidly, causing the pipe to rupture. 　　⑶When the fluid from a source at a higher elevation is conveyed downstream at a certain speed through gravity flow, rapid closing of the valve upstream causes the liquid column in that section of the pipe to not stop moving immediately due to the effect of gravity and the inertia of the flow. It continues to flow downstream at the same speed. As a result, a vacuum is created in the pipe since no air can enter in time, leading to the pipe being crushed by negative pressure and damaged. 　　Hazards of the water hammer effect: The pressure increase caused by water hammer can reach several times, or even dozens of times, the normal operating pressure of the pipeline. Such large pressure fluctuations cause severe vibrations in the piping system, and may even lead to the separation of pipe joints.