- When an open valve is suddenly closed, the water flow generates pressure on the valve and pipe wall. Due to the smooth pipe wall, the subsequent water flow in the role of inertia, rapid increase, and produce destructive effect, which is positive water hammer. Close the valve will also produce water hammer after a sudden open, called negative water hammer, also has a certain destructive force, but not as big as the former. Electric pumping unit sudden power failure or start, the same will also cause pressure shock and water hammer effect. This pressure shock wave spreads along the pipeline, which can easily lead to local overpressure in the pipeline and cause pipeline rupture, damage to equipment and so on.
For the delivery of saturated steam piping system, if the pipeline due to test run in the process of water storage, switching valves too fast is more likely to exceed the normal water hammer plunger flow superposition effect --- incompressible water in the high flow rate of steam to promote the production of a great deal of kinetic energy (the quality of the water and the steam of the high flow rate of the common effect), this energy is very easy to cause the cut-off valve closure parts of the burst or pipeline weld seam tearing, causing accidents.
- Conditions of water hammer
1. Sudden opening or closing of the valve;
2. Pump unit suddenly stop or open;
3. Single pipe to the high water supply (water supply terrain height difference of more than 20 metres);
4. The total head of the pump (or working pressure) is large;
5. Excessive water velocity in the water pipeline;
6. The water pipeline is too long, and the terrain changes.
7. If the gas-liquid two-phase pipeline liquid storage, then the operation of the pipeline before the valve is opened rapidly is more dangerous.
- Hazard of water hammer effect
Water hammer caused by the pressure rise, up to several times or even dozens of times the normal working pressure of the pipeline. This large-scale pressure fluctuations, the harm caused by the piping system are mainly:
1. Causing strong vibration of the pipeline, pipeline joints disconnected;
2. Destruction of valves, serious pressure is too high to cause pipe burst, water supply network pressure reduction;
3. Too low pressure leads to pipe deflation, but also damage to valves and fixtures;
4. cause pump reversal, damage to equipment or piping in the pump room, serious flooding of the pump room, resulting in personal injury and other major accidents, affecting production and life.