Waterhammer Caused by Intermittent Pump Failure in Pipe Systems Including Parallel Pump Groups

The use of pumps linked in parallel or series in large scale pipe systems is usually inevitable, to meet the required head and discharge. Transient flow occurs following a pump failure in a pump group as a result of variations in the flow rate. This research is an investigation about waterhammer caused by one or more pump-switch off in a pump group when they are connected in parallel. The operation of each pump in the group during steady and unsteady state is analyzed. For this purpose, the fluid flow equations as well as the pumps relations including rotational speed change and head loss are combined and simultaneously solved in the time domain by the method of characteristic. From the results one can quantitatively conceive that the intermittent shut-down compared to suddenly switching off the whole pump group produces much less waterhammer pressures. Furthermore in the intermittent shut-down with different pump characteristics, it is suggested to firstly switch off the most powerful pump, and then the rest which are weaker. Appropriate interpretation about the transition results have been included.