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How to eliminate water hammer in plastic pipes?


What is water hammer?


In the pressure pipeline, the valve opens or closes too fast or the pump suddenly stops, causing the liquid flow rate to change sharply, causing the instantaneous pressure to change significantly, repeatedly and rapidly, resulting in a strong shock wave of water flow to the pipeline and valve, and the appearance of "cavitation". "Phenomena, like a hammer beating, and accompanied by a "bang bang" sound of water, so it is called water hammer.


The occurrence of water hammer causes the pressure in the pipeline to increase sharply to several times or even ten times higher than the normal pressure, which is very harmful and affects production and life. If the pressure is too high, it will cause the rupture of the pipe. On the contrary, if the pressure is too low, it will cause the collapse of the pipe and damage the valve and fixing parts.


When the open valve is suddenly closed, the water flow will produce a pressure on the valve and the pipe wall, mainly the valve. Due to the smooth wall of the pipe, the subsequent water flow quickly reaches the maximum under the action of inertia, and has a destructive effect. This is the "water hammer effect" in hydraulics, that is, positive water hammer.

Negative water hammer.gif

After the closed valve is suddenly opened, it will also produce water hammer, called negative water hammer, which also has a certain destructive power, but it is not as large as the former.

Positive water hammer.gif

How does water hammer occur?


Water hammer is prone to occur in the following situations.

1. The valve opens or closes suddenly;

2. The water pump unit encounters a power failure and suddenly stops or automatically starts;

3. A single pipe delivers water to a high place (the height difference of the water supply terrain exceeds 20 meters);

4. The total head (or working pressure) of the pump is large;

5. The water velocity in the water pipeline is too large;

6. The water pipeline is too long and the terrain changes greatly.


The dangers of water hammer:


The pressure increase caused by water hammer can reach several times, or even dozens of times, the normal working pressure of the pipeline. Such large pressure fluctuations mainly cause harm to the pipeline system:

1. Cause the pipeline to vibrate strongly, and the pipeline joint is disconnected;

2. Destroy the valve, the serious pressure is too high, causing the pipeline to burst, and the pressure of the water supply network is reduced;

3. If the pressure is too low, it will lead to the collapse of the pipe, and also damage the valve and fixing parts;

4. Cause the pump to reverse, damage the equipment or pipelines in the pump room, cause serious flooding of the pump room, cause personal injury and other major accidents, and affect production and life.



The basic measure to prevent water hammer is to slow down the change of flow rate as much as possible during the transition period. Almost all devices used to prevent water hammer are designed for this purpose. These devices can be divided into the following three types according to their purpose of use:


(1) Slow down the change of flow rate----increase the diameter of the water pipeline and increase the project investment


(2) Prevent pressure drop ---- adjust the opening of the pump outlet valve, adjust the flow and lift


(3) Limit pressure rise ---- set pressure reducing valve


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