About air hammer and water hammer

Thread Content

During the construction and testing of the pilot plant, I encountered interference from water hammer and air hammer. I would like to share this with you. The level difference between E19 and D27 is about 10 meters. D27 has an overflow pipe leading to E19 below. During operation, because the pipe is too thin and the drop is large, a siphon phenomenon occurs, causing the liquid in the pipe to be mixed with gas, resulting in an air hammer. In addition, vibration is often encountered on steam pipelines, which is actually a water hammer phenomenon. So what is air hammer or water hammer? Water hammer is also called water hammer. During the transportation of water (or other liquids), due to sudden opening or closing of valves, sudden stops of water pumps, sudden opening and closing of guide vanes, etc., the flow rate changes suddenly and the pressure fluctuates significantly. 　　The water hammer effect is a vivid term. It refers to a severe water hammer caused by the water flow hitting the pipe when the water pump is started and stopped. Because inside the water pipe, the inner wall of the pipe is smooth and the water flows freely. When the open valve is suddenly closed or the water pump is stopped, the water flow will generate a pressure on the valve and pipe wall, mainly the valve or pump. Because the pipe wall is smooth, under the action of inertia of the subsequent water flow, the hydraulic force quickly reaches the maximum and produces destructive effects. This is the "water hammer effect" in hydraulics, that is, positive water hammer. On the contrary, when a closed valve is suddenly opened or the water pump is started, water hammer will also occur, which is called negative water hammer, but it is not as big as the former. 　　The instantaneous pressure generated by water hammer can reach dozens or even hundreds of times of the normal operating pressure in the pipeline. Such large pressure fluctuations can cause strong vibrations, noise, and possible damage to valve joints in the piping system. It has a very damaging effect on the piping system. In order to prevent water hammer, the pipeline system needs to be designed correctly to prevent the flow rate from being too high. Generally, the designed flow rate of the pipe should be less than 3m/s, and the valve opening and closing speed needs to be controlled. 　　Because the pump is started, stopped, and valves are opened and closed too quickly, the speed of the water changes drastically, especially the water hammer caused by a sudden stop of the pump, which can damage pipelines, water pumps, and valves, and cause the water pump to reverse and reduce the pressure of the pipe network. Water hammer effect is extremely destructive: If the pressure is too high, it will cause the pipe to rupture. On the contrary, if the pressure is too low, it will cause the pipe to collapse and damage the valve and fixing parts. In a very short time, the water flow rate increases from zero to the rated flow rate. Since fluids have kinetic energy and a certain degree of compressibility, huge changes in flow rate in a very short period of time will cause high and low pressure impacts on the pipeline. The pressure impact will cause the pipe wall to be stressed and produce noise, just like a hammer hitting the pipe, so it is called the water hammer effect. In fact, there is another reason for the occurrence of air hammer or water hammer, which is the inclusion of gas in the pipeline carrying liquid. Since the flow rate of the gas phase and the liquid phase in the pipeline is very different, when the gas phase is introduced into the pipe, the flow rate is very high. If there is liquid in the pipe, it will advance at a high speed driven by the gas, hit the pipe wall and pipe fittings, and make a hammering sound, which is an air hammer. In the same way, when there is liquid in the gas pipeline, water hammer will occur. The danger of water hammer or air hammer is that it may damage valves or pumps, or even cause pipes to break due to resonance. The level difference between E19 and D27 is about 10 meters. During operation, because the pipeline is too thin and the drop is large, a siphon phenomenon occurs, causing the liquid in the pipeline to be mixed with gas, resulting in an air hammer.