PVC pressure pipes are designed ont he basis of burst regression line for pipes  subjected  to constant internal pressure. This long term testing  and analysis allows nominal pressure classes to be allocated to pipes. However other factors must be considered, including the effects of dynamic loading while most gravity pressure lines normally operate under constant pressure, pumped lines frequenty frequently do not. Pressure fluctuations in pumped mains result from events such as pump start up and shut down valves opening and closing. it is essential that the effect of this type of loading be considered in the pipeline design to avoid premature failure .

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