Pressure drop in pipelines due to pump trip event

Abstract

We consider the pressure pulse or surge in a pipeline due to an unplanned sudden shutdown of a pump system in the pipeline network. This is known as water hammer. Our primary focus is the negative pressure pulse that travels downstream from the pump(s), is reflected with a sign reversal from the end, and travels back to the pump(s). As part of the preliminary design of a pipeline it is necessary to determine the minimum head envelope associated with such an event, which is used to determine where surge protection will be needed in the pipeline. Of particular interest is whether the initial head drop at the pump(s) due to a sudden drop of the flow speed to zero, as given by the Joukowski formula, gives a sufficiently accurate prediction of the minimum head at the pump(s). This minimum head is used to construct the minimum head envelope for the downstream pipeline. An examination of the relevant literature along with solution of the water hammer equations shows that, assuming the flow speed falls instantaneously to zero at the pump(s), the total drop in head at the pump(s) is given by the sum of the initial Joukowski head change and the friction loss under normal operating conditions. While the friction loss may not be significant in short pipelines, in long pipelines it cannot be neglected.