Optimization Of Valve Adjustment For Reducing The Closing-valve Water Hammer Damage

The water resources in our country have a lot of problems such as the unevendistribution and so on, so there are more and more long-distance water transfer projects.But due to the presence of a variety of adverse conditions, which will lead to a lot ofproblems that may affect the safety of the water transfer process, of which transientflow is an important factor, and water hammer phenomenon is the most representativeone. This paper studied the valve adjustment including single-valve adjustment andmulti-valve adjustment to reduce the hazards of the water hammer caused by the valveclosure to the piping system.Water hammer wave propagation process in the pipeline is very complex, when thewaves are produced, along with the reflection, the wave will cyclical spread in thepipeline. Reasonable closure rules when using single-valve adjustment to make themaximum water hammer pressure minimum which is caused by the wave superpositionwhen the valve closing. This paper based on the continuity equation and the motioneaqtion of water hammer, with the method of characteristics, used the correspondingprogramming to simulate the water hammer wave propagation when the boundaryconditions are obtained. After caculating, the maximum water hammer pressure can beobtained, and the best closure of the valve can also be obtained by the principle that themaximum water hammer pressure minimum, and compared with the result obtained bythe Joukowski formula, the effect of the optimization method is more pronounced.When the topography in the water transfer process is complex and the distance ofwater transfer pipeline is so long that using single-valve adjustment has some certainlimitations, another valve can be set in the feature points of the pipeline, which canartificially manufacture water hammer wave sources, according to the superpositionprinciple of the wave to use the multi-valve adjustment to optimize water hammer. Inthis paper, after the computational analysis, the boundary conditions of the two-valveadjustment can be obtained, after the study of the installation location and the beginningclosure time of the middle valve, obtained that the best installation location is in thetwo-thirds of the pipeline, and when the water hammer travelling half pipeline cycle, themiddle valve begines to close the best closing time, and according to the maximumwater hammer pressure generated by the closure of two valves when the valves closingby different ways, to determine the best closure combinations when using two-valveadjustment, which can ensure that the negative pressure won’t appear in the pipeline andin the pipeline the maximum water hammer pressure minimum.Finally, according to the above analysis method, calculation and analysis foranother example to step forward to determine whether the conclusions above and theoptimization curves are still applicable when conditions of the pipeline change. After discussion, the best installation location and the beginning closure time of the middlevalve is still applicable, and when the pipeline cycle of the water hammer wave isapproximately equal, the optimization curves of the single-valve and two-valveadjustment is still applicable, however, when the pipeling cycle varies greatly, thecurves are no longer applicable. This paper also discussed the different factors whichmay influence the two-valve adjustment, such as the closing sequence，the non-constantfriction in the pipeline and so on, to determine the nessicity of the first closing time ofthe ending valve, and the nessicity of the situation that regarding the friction as constant,to taking a step forward to improve the theory of two-valve adjustment.