System-Improvement Method
This method is the most reliable, with the least operation and maintenance requirement. However, it is very expensive and usually used only as a last resort. It consists of the following measures:
- Reduce velocity—The smaller the pipe flow velocity, the less potential there is for a large rate of change in velocity (dV/dt). Normal velocities can be reduced by enlarging the pipe diameter or redistributing the flow to twin pipes.
- Pipe material—The pressure wave speed a of a flexible pipe material is less than that for rigid pipe. For a very fast stoppage of flow (< 2 L/a), the transient effect of pressure-wave speed is prominent. Changing pipe material may improve the outcome, although the surge tolerance of a more flexible pipe may be less.
- Pipeline improvement—Pipeline profiles with prominent local high points are susceptible to the occurrence of subatmospheric or even full vacuum pressure, resulting in water-column separation and vapor or air pockets in the pipeline. Very high upsurge pressures can result when water columns subsequently rejoin. Extra excavation or fill can reduce or eliminate local high points.