Abstract: To study the pressure diversion system of a throttled surge tank connected to a long link pipe, the influence of the pipe length on water hammer passing through the tank was examined and derive an equation for the coefficient of water hammer was derived simulating a system of a case study project. With a link pipe shorter than 10% of the diversion tunnel length, water hammer coefficient, peak pressure at the end of volute, and peak pressure in the tunnel were found to vary in the ranges of 10%, 1% and 2% respectively. If the pipe length exceeds this 10% threshold under certain layout requirement, its influence should be considered and tunnel lining requirement be modified accordingly. The coefficient decreases with the increasing diameter of the link pipe or the impedance hole, depending more on the latter. For impedance holes with small diameters, the coefficient can be significantly reduced if the pipe takes the same diameter, whereas it is smaller if the pipe has a slightly larger size than the impedance hole for large impedance holes.

Key words: hydropower station, water hammer passing through surge tank, long link pipe, throttled surge tank, maximum pressure at volute end, maximum pressure of diversion tunnel