Research On Structural Parameter Of Air-valve And Water Hammer Protection In Transmission Pipeline

There are many safety matters which caused by water hammer is particularly severe in the process of long-distance water supply.Air valves can be used to eliminate the negative pressure in the pipeline during the water hammer process,compared with other protective equipment,air valves also have the advantages of lower price,simpler design structure,and less limited installation conditions,which thus are widely used in water conveyance systems.However,due to the current arrangement of air valves in the pipeline,only the experiential reference distance and installation position can be used.The traditional air valve is designed to solve the negative pressure of pipelines,but a higher positive pressure of water hammer is caused by its feature of fast exhaust.Therefore,research on the internal structure and related characteristic parameters of air valves has very important practical and theoretical values.In the paper,the method of simulation calculation was used to conduct the following work:(1)The basic differential equation of water hammer and the characteristics method used in the calculation of water hammer were discussed,and various boundary conditions required for the calculation of water hammer caused by pump failure were established.(2)The internal structure of a traditional air valve was modified to an air valve with the characteristic of "fast intake and slow exhaust".In another word,it has the capability of fast intake during the intake phase,which helps to eliminate the negative pressure.Meanwhile,it has the capability of slow exhaust during the exhaust phase,helping to prevent the occurrence of water hammer and reduce the positive pressure of water hammer.(3)A numerical analysis was performed on the internal flow field of the two different air valves,resulting in intake and exhaust flow curves under different working conditions.The effects of the structure-improved air valve on water hammer protection were explored,and the influencing factors of water hammer protection were studied which mainly include the diameter of air valve,the orifice area ratio of air valve,and the arrangement of air valve.(4)In the engineering example,the water hammer caused by pump failure under four different pump working conditions was calculated.For the full-speed pump working condition with the most serious effect on water hammer caused by pump failure,a safe and reliable protection scheme for structure-improved air valve was proposed,based on the results of influencing factors analysis of water hammer.