Study on the factors influencing air valve protection against water hammer with column separation and rejoinder

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.