The theoretical study and parameter optimization of two-stage air valve for prevention of water hammer in the long supply pipe

The location of two-stage air valve is usually installed in accordance with the experience and the related parameters are determined through repeated trial since the commercial software of water hammer calculation does not open the background. In this paper, the long-distance water pipeline was simulated using C++ programming to analyze suddenly pump stop event and genetic algorithm was adopted to optimize the parameters of air valve. Firstly, the boundary condition of the air valve and the theoretical calculation of the installation location had been established. Then, engineering examples under three conditions were programmed, which included (1) no protective measures after stopping the pump; (2) installation of the two-stage butterfly valve; (3) the installation of a two-stage butterfly valve and air valve joint protection. Finally, the optimal close process of the two-stage butterfly valve and the best intake and exhaust coefficient of the air valve were obtained by genetic algorithm. The results showed that: a two-stage valve installed can reduce the maximum positive and reverse speed control of pumps, while reasonable installation of air valve can effectively alleviate the negative phenomena. The location of the air valve was reliable on the basis of pressure judgment method(method two)or theoretical formula(method three).The maximum pressure in the pipeline was reduced with the increase of the area ratio of air valve μ when 0.1 ≤ μ ≤ 0.3 and was firstly decreased then increased with the increase of critical pressure P_cr. The results of after optimization and optimization of pre-computed are compared to indicate that the optimized parameters can be better for protection of water hammer, overcoming the deficiencies of commercial software.