Based on water hammer theory and the Characteristic Method,a long-pipeline pumping station system with the pipe diameter of 2.2 m was studied under the pump shutdown operation condition.The numerical results indicated that negative pressures were existed along the pipeline under the condition,and the maximum negative pressure is-5.9 m.According to the regular arrangement principles of air valves,18 air valves were installed along the pipeline to control the negative pressure.Three different flow coefficients which are 0.95 and 0.65,0.75 and 0.45,0.62 and 0.62,and three different orifice sizes which are 0.018,0.071,0.196 m2 of air valve were analyzed and compared respectively.The maximum negative pressure are-0.69,-0.70,0.71 m under three different flow coefficient,and-0.88,-0.69,-0.67 m under three different orifice sizes.It is found that the parameters combination in which air valve size is 0.196 m2,inflow coefficient is 0.95,and outflow coefficient is 0.65,is suitable for the pumping station with pipe diameter of 2.2 m
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