Air valves are used to suppress negative water pressures in water transmission pipelines. They also play a key role during the water filling and drainage stages in pipeline systems. However, systematic guidelines for the selection of air valve parameters are lacking. In practical engineering applications, the selection is mainly based on personal experience. If the selected parameters are not appropriate, negative pressures can occur in a pipeline due to insufficient air inflow or destructive water hammer pressures with column separation and rejoinder, which are caused by rapid air discharge. Given the subjectivity of the selection of air valve parameters in engineering applications, this paper introduces the structure and working principle of two different types of air valves. Combined with engineering examples, the one-dimensional transient flow elastic model and the characteristic method are used to conduct numerical simulations in MATLAB to investigate the influences of the air valve type, the inlet and outlet orifice diameters, and the inflow and outflow discharge coefficients on protection against water hammer with column separation and rejoinder. The inflow and outflow coefficients of the anti-slam air valve have a slight influence on preventing water hammers with column separation and rejoinder. The research results provide a theoretical basis for the rational selection of air valves in practical engineering applications.
Discharge matching of high lift conveyance cascade pumping station has great influence on safe and economic operation of the project. The main influencing factors of cascade pumping station discharge matching are water quality, performance changing of pumps during their operation, pump characteristic differences and system characteristic curve, etc. The discharge matching methods of cascade water lifting project are distributing flow regulation, throttle regulation, variable speed regulation and pump startup or shutdown regulation, etc. If the cascade water lifting project has enough regulation volume or distribution flow between pumping stations, startup or shutdown regulation can be considered. For the project that has no such conditions, variable speed regulation should be used.
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