Abstract: The water hammer effect in pipeline has become increasingly acute with the development of water-saving pipe network technology. To investigate the influence of branch pipe diameter on water hammer pressure of pipe network, the fluctuation of water hammer pressure was examined via numerical computation using Pipenet software. Two working conditions were designed. One is to close suddenly the branch pipe valve (working condition one), and the other is to close the main pipe valve (working condition two). In both conditions, there is only one branch in the pipe network. Five pipe types (DN110, DN90, DN75, DN63 and DN50) were selected in the study. Moreover, the variation law of maximum water hammer pressure under the two working conditions was analyzed by theoretical method. Results revealed that the maximum water hammer pressure at each valve and the water hammer pressure on pipe both increased with the reduction of branch pipe diameter under the two working conditions; reducing the branch pipe diameter had greater impact on working condition one in comparison. Theoretical analysis showed that the main reason for the rise of water hammer pressure along with the recession of branch pipe diameter lies in the increment of flow velocity in branch pipe in working condition one, and the reduction of the reflected buck wave in working condition two.

Key words: branch pipe diameter, branched pipe network, water hammer pressure, numerical computation, theoretical analysis