Water hammer refers to the phenomenon of large pressure fluctuations and vibrations caused by abrupt changes in fluid flow in a closed piping system (including water pump). Its instantaneous pressure can greatly exceed normal pressure and often has devastating effects. In order to prevent or reduce the water hammer effect, corresponding elimination measures can be taken, such as delaying the opening and closing time of the pipeline or pump, installing a water hammer eliminator, and the like.
The instantaneous pressure generated by the water hammer can reach several tens of times or even hundreds of times the normal working pressure in the pipeline. This large pressure fluctuation can cause strong vibration or noise in the piping system and may damage the valve joint. It has a great destructive effect on the pipeline system. In order to prevent the water hammer from correctly designing the pipeline system and preventing the flow rate from being too high, the flow rate of the designed pipe should be less than 3m/s, and the opening and closing speed of the valve should be controlled.
Because the pump is turned on, the pump is stopped, and the switch valve is too fast, the speed of the water changes drastically. In particular, the water hammer caused by sudden pump stop can damage the pipeline, the water pump, the valve, and cause the water pump to reverse and the pressure of the pipe network to decrease. The water hammer effect is extremely destructive: if the pressure is too high, it will cause the pipe to rupture. Conversely, if the pressure is too low, it will cause the pipe to collapse and damage the valve and the fixing member. In a very short time, the flow of water is from zero to the rated flow. Due to the kinetic energy and a certain degree of compressibility of the fluid, a large change in flow in a very short period of time will cause excessive and too low pressure on the pipeline. The pressure shock will force the pipe wall to generate noise, just like a hammer hitting a pipe, so it is called the water hammer effect.
Causes
1.Cold water entry
Condensate is generated on the steam mains due to radiation heat dissipation. The high-speed flow of steam in the pipe causes the condensate to flow together to cause enthalpy. In this case, as the steam drives the condensate, it gradually forms a certain scale in the pipeline. This is similar to the formation of huge waves due to strong winds.
In this case, the water hammer phenomenon occurs when the condensate violently hits the elbow or a closed valve.
2.Steam condensation
When steam loses heat, it turns into condensate, which is 1000 times smaller than steam. Therefore, when the steam enters the condensed water which is in contact with the low temperature to cause condensation, the volume of the steam immediately changes greatly.
When the steam is in the process of condensation, the vacuum is temporarily formed due to the volume reduction, so the condensed water in the pipe is sucked into this vacuum space. In this case, a water hammer is formed, and the condensed water forms a collision with each other in the pipeline.In short, mixing low temperature condensate in the pipeline with steam is very dangerous. However, such a situation is very common, as in a condensate recovery system or a similar system, which is a very difficult form of water hammer.
It is worth noting that this type of water hammer is not only found in condensate recovery systems, but also in steam distribution piping and steam equipment.
