Study On Optimization Of Air Valve Parameters In Long Distance Water Supply Pipelines

As long distance water supply pipelines are limited by some external factors, suchas terrain conditions, buildings and so on, resulting in large pipeline ups and downsand unstable flow condition. It’s easy to produce complex hydraulic transients.Especially, when the pump suddenly stops running, water column separation will occuron the pipelines. What’s more serious is that it would cause pipe rupture, water supplyinterruption and equipment damage. It will produce a huge economic loss. Asnecessary water hammer protective measures, the study on the protective effect andparameter optimization of air valves have an important practical significance.First, this paper introduced the basic equation of water hammer and the method ofcharacteristics in detail, and then set up all kinds of basic boundary conditions,pumping accident boundary conditions and air valve boundary conditions. Then, itdescribed the role of air valve, the type of air valve and the operational principle of airvalve. Combined with practical engineering, this paper conducted hydraulic analysis ofsteady state conditions and pumping accident conditions, and then it carried onnumerical simulation for some working conditions, such as without any protectivemeasures, check valve after the pump two-phase closed, installing one-phase closed airvalve and installing two-phase closed air valve. It also compared the water hammerprotective effect between one-phase closed air valve and two-phase closed air valve,and used commercial software to check the results of process simulation. Finally, thispaper conducted an optimization research for these parameters, which are air valveinstallation position, air valve inlet and discharge coefficient, air valve inlet anddischarge area, critical pressure and check valve closed law, and made a sensitivityanalysis to identify these parameters’ setting rules.The study of air valve water hammer protection showed that reasonablearrangement of air valve in the long distance water supply pipelines could reduce thenegative pressure effectively, but the positive pressure would increase. Although theprotection of negative pressure was similar between one-phase closed air valve andtwo-phase closed air valve, there were obvious differences on the protection of positivepressure. By comparison, it was found that the water hammer protection of two-phase closed air valve was superior to one-phase closed air valve. Therefore, practicalengineering should choose two-phase closed air valve as the protective measures forpumping accident. The study of two-phase closed air valve parameter optimizationshowed that it should be combined with water hammer calculation to determine theposition and aperture of air valve in practical engineering, and the bigger of air valveinlet coefficient, water hammer protection was better; air valve discharge coefficientcould not be too big, also not too small; the size of two-phase closed air valve criticalpressure had little impact on positive pressure, but it had great impact on negativepressure; the longer of the check valve’ s slow closing time, the smaller maximumpressure would be, but backflow phenomenon would be more serious; the fast closingtime of check valve after pump could not be too big, also not too small; the smaller ofcheck valve’ s fast closing valve opening in a certain range, the smaller maximumpressure would be.