Study On Water Hammer And Its Protection In Water Transportation System Of Mountainous Urban

With the acceleration of urbanization in China,the construction of water supply projects in mountainous urban is an inevitable trend of social sustainable development.Requirements for municipal water supply are increasing day by day,ensure the safety of water supply is the first priority for water delivery projects.The phenomenon of water hammer is one of the major causes of safety accidents in water delivery projects.In particular,the structure of the water pipelines in mountainous towns is complex and It is more prone to occur the water hammer of cavities collapsing,which is more harmful.Therefore,water hammer protection analysis is conducted on the water pipelines to simulate and study the transient flow process under various working conditions;to put forward safety,reliable,economical and suitable water hammer protective measures;to avoid the accidents triggered by water hammer;which is meaningful and valuable to improve standards of technology,decrease projects costs and make sure the water delivery projects can work safely.Firstly,summarized the basic theory and calculation method of water hammer.Secondly,build up the mathematical model for the project example of pressurized water transportation system in mountainous urban,discussed the applicability and aperture optimization settings of different kind of air valve at pressurized water transportation system and optimization settings of pump's outlet valve two-stage closing procedure when accidental operating conditions of pumps occurred power off.And then,set up the mathematical model for the project example of gravity flow water transportation system in mountainous urban,investigated the applicability and aperture optimization settings of different kind of air valve at gravity water transportation system and optimization settings of valve two-stage closing procedure when the valve closed at the end of the system.Finally,a mathematical model was established for long-distance series pressurized water transportation project in mountainous urban,the water hammer protection measures and technical renovation plans for water transportation system were put forward against the problem of water supply safety in engineering examples.The main findings are as follows:? The water hammer protection caused by stopping pump in pressurized water transportation system and caused by closing valve in gravity water transportation system at mountainous urban,The water hammer protection with ordinary air valve is not much effective which is not suitable for water hammer protective measures in this sort of water transportation systems.It can made a positive effect on water hammer protection when chose suitable diameter ratio of orifice ? =0.02-0.10 for air valve groups,which is desirable water hammer protective measures for such water transportation systems.? The pump's outlet valve two-stage shutdown program settings should be:fast-closing time t1 = Ci ?2Li/ai,should choose1.13-1.18;fast-closing angle ? just haslittle affects to water hammer protection,? should choose 65-75°;slow-closing time t2=C2·t1,C2 should choose 10.0-10.7,when the pump stop occurred accidental power off in pressurized water transportation system at mountainous urban.? When the valve at the end of gravity water delivery system in the mountainous urban is closed,the two-stage closing procedure for the end of the pipeline valve shall be set as follows:According to the characteristics of the resistance coefficient of the butterfly valve,the valve opening at 5%of the flow coefficient is divided into two phases,namely the closing angle 66° should be selected;the slow closing time has less impact on the water hammer protection,and 1.3-2.0 should be selected for the value of C2;the optimization of the valve closing time is the inverse problem of the hydraulic transition process.The interval elimination method is used to solve the fast-closing time and thefast-closing time t1 = C1?2Li/ai,2.85-2.90 should be selected for the value of C1.? Actual project of long-distance series pressurized water transportation system in mountainous urban in southwestern China adopts comprehensive control measures of flow control valves,overpressure relief valves,and air valve groups;It can not only reasonably distribute the flow of water in high level pools with different elevations,but also effectively prevent the phenomenon of water hammer and improve the safety of water supply.This way has the characteristics of low investment and low installation requirements,and can provide reference for other long-distance series pressurized water transportation projects in similar mountainous urban.