Numerical analysis of the hydraulic transient in a closed pipe in presence of a bypass valve

Hydraulic transients generated when sudden changes in flow rates occur in a pressurized pipeline system were and are still today a crucial technical aspect of their operation. This is a common concern of hydraulic engineers aiming to reduce pressure waves in order to limit their related effects onto the hydraulic system components. From this perspective, the presence of a bypass system is recognized as useful to reduce the maximum water hammer overpressure during a pipeline closure; however, the sizing of bypass system is usually heuristic. This paper investigates the sizing procedure for a bypass system (i.e. pipe and valve) mainly considering the overpressure reduction values as dependent on some typical parameters for such pipe systems. A numerical model is used to investigate the efficiency of a bypass system in reducing the maximum water hammer overpressure, showing that an optimally designed bypass system allows to completely close a pipe in a lower time simultaneously saving the integrity of existing devices. Results show that the optimal diameters for a bypass valve is comprised in the range of 20%–40% of the main pipe diameter. In this way, a bypass system allows an overpressure reduction higher than 70%, which is important for faster manoeuvres.