Numerical calculation of air pressure changes in water filling and emptying process of pressured-pipeline with combined air valves

In order to research on the water filling and emptying process of a pressured-pipeline in long distance, according to the characteristics for the pressured-pipeline in the long distance during the filling and emptying process, the strategies of sectional treatment and water filling and emptying in succession were adopted. For each segment of the pipe, a mathematical model was established with using the ideal gas equation according to the filling principle under the low flow rate in combination with the characteristics of inlet and exhaust gas of an air valve. On the basis of the definite positions of air valves and drain pipes, calculating the air pressure changes in different pipes according to the definite water filling discharge and different water emptying discharges. The calculated results indicate that in accordance with the principles of the low flow rate of water filling, the air pressure inside the pipe is not high. The greater the water emptying discharge, the lower the corresponding air pressure and the higher pipe risk. These computation results can provide safety assessment foundations for the pressured-pipeline filling and emptying process in the long distance.