The Study On Model Selection And Protective Effect Of Air Inlet And Release Valves In Long-distance Water Supply Pipelines

Water deficience, water distribution’s unevenness in time and space, serious water pollution,that’s the reality of the situation in our nation. With the rapid growth in national economy and sharp increase in water consumption, water resource shortage is aggravated constantly, and the exploitation and construction of large-scale, long-distance, cross-basin water supply project has been an emergency. Because of the long transfer distance and drastic undulating pipeline, if the exhaust system in the pipeline doesn’t work well,this water supply systems are easy to burst, which always causes huge economic loss and harms the steadiness and security of the system. The air inlet and release valve has been a common equipment in the actual water supply project, because it can suppress efficiently liquid column separation phenomenon and sudden increase of the pressure. Meanwhile, it structures simply, costs comparatively low, installs easily, and requires easy installation conditions. However, due to the lack of corresponding design standards and specifications, the air inlet and release valve is almost set up by experience. Water hammer pressure in the pipeline was changed by adding quantity or raise the specification of the valve. As a result, many projects won’t run normally or even burst after a period. For this reason, the study on air inlet and release valve’s rational model selection has become more and more important.Basing on the understandings above, the main content of this paper is as follow:(1) Basing on the structure of the common air inlet and release valve and its technical performance characteristic, a mathematical model for water hammer under the protection of air inlet and release valves was developed.(2) The study about exhaust discharge coefficient. Equations about exhaust discharge coefficient of air inlet and release valves at various pressure differentials have been built. On this basis, a numerical simulation of hydraulic transient under the protection of the air inlet and release valve had been carried out, with an expection of a numerical simulation result more close to the real state of the water supply system.(3) Improve the mathematical model of the water hammer under the protection of the air inlet and release valve. Under the hypothesis that the air in the pipeline follows the polytropic process, the mathematical model of the air inlet and release valve was improved, and a new boundary condition as well as the numerical equations were proposed.(4) A numerical simulation system of hydraulic transient under the protection of the air inlet and release valve in pump stations was developed with Visual Basic6.0, which has full functiones, simple operations, reliable performances and friendly user interfaces.(5) The study on the model selection of air inlet and release valve in the long-distance water supply pipeline. A simulation with different parameters of the air inlet and release valve in the pipeline had been carried out using the developed hydraulic transient numerical simulation system in pump station, in the purpose of studying the model selection method of the air inlet and release valve in the long-distance pipeline in the pump station.(6) This study simulated hydraulic transient in the water supply pump station of Shanxi LuAn resin co., LTD in order to determine the safety protection manner of this water supply system.According to the study, this paper (1) On the basis of the traditional mathematic model of the air inlet and release valve, proposed the best shutoff stroke of the two-stage hydraulic controlled slow closing butterfly valve in the pump outlet in the pump station of Shanxi LuAn resin co., LTD as well as the number, locations and the specifications of the air inlet and release valve needed in the pipeline.(2) Suggest that a dynamic discharge coefficient for the air inlet and release valve, which is based on the the measurements, should be used in the hydraulic transient numerical simulation under the protection of air inlet and release valve in water supply pump station. Meanwhile a methond to determine the dynamic coefficient was given in the paper so as to simulate the outflow and inflow of the air inlet and release valve more accurately.(3) Compare with the the original model, the new model is more rational, because it used the polytropic process hypothesis, considering the condensable and inflatable thermal conductivity of the air in the pipeline.(4) Basing on the water supply pump station of Shanxi LuAn resin co., LTD, propose for the first time the procedures and methods of the model selection of the air inlet and release valve in the long-distance pipelines.One promising area for further study is the common criteria of the air inlet and release valve model seletion as well as the the optimization of the mathematical model.