Study On The Influence Of Check Valve Closing Characteristics On The Transient Hydrodynamic Parameters Of Pipes

Check valve is used to prevent the backflow of the liquid,which is an essential part of the pump system.However,due to the fast closing characteristics of the check valve,the fluid dynamics parameters in the pipeline system are changed instantaneously,then a water hammer is generated.The appearance of the water hammer will damage the equipment,and even cause serious injury or death.Therefore,it is important to study the dynamic characteristics of the check valve when it is closed momentarilyand to take measures to control the check valve closing time to prevent water hammer.This paper mainly studies the relationship between the opening and closing characteristics of the two-way switching valve in the dual-circuit pump valve system and the transient hydrodynamic parameters of the pipeline in the shipboard power system.The aim is to explore the precautions for water hammer in a dual-circuit pump valve system.In this paper,numerical simulation and experimental research are combined to simulate study the pipeline hydrodynamics.The main research work includes two parts.One is to study the existing calculation method of water hammer and seek a more accurate calculation method of water hammer.The other is to simulate the double-loop pump valve system based on the existing calculation method and propose prevention measures for the water hammer.The main work and conclusions are as following:The water hammer test bench was used to compare the commonly used characteristic line method,wave characteristic method and the accuracy of commercial Pipe Surge software.The results show that the positive maximum water hammer pressure calculated by the characteristic line method is basically consistent with the experimental test results,and the error is about 5%.However,the wave velocity and the negative pressure of the water hammer calculated by the characteristic line method are inconsistent with the experiment,which indicates that the characteristic line method cannot consider the vapor-liquid bridged water hammer generated when the water column is stretched;due to the time relationship,the wave characteristic method The research and understanding are still relatively shallow.The curve of the water hammer positive pressure can only be calculated by the wave characteristic method.The calculated maximum water hammer pressure is completely consistent with the experimental results.The commercial Pipe Surge software test shows that the software can simulate steam.The liquid water hammer was used to calculate the maximum water hammer pressure,water hammer velocity and water hammer negative pressure,which were all consistent with the experimental results.Aimed at the theoretical defect that the water hammer velocity is assumed to be fixed in the traditional research,this paper analyzes the influence of bubble content on the water hammer velocity,and verifies the conclusion that the water hammer velocity changes with the bubble content by experiments,and finds the characteristic line.The reason why the water hammer velocity obtained by the characteristic line method does not match the experimental results.Based on the research on the accuracy of the water hammer calculation method,Pipe Surge software was used to simulate the opening and closing time of the check valve and the water hammer generated during the two-way switching of the dual-circuit pump valve system.For the axial flow check valve,the simulation results show that the main road closing time is 5s,the bypass opening time is 0.9s,and the spring elastic coefficient k is 6967.5N/m,when the main circuit check valve is closed.There will be a water hammer,but there is a pump backflow of-56.4m~3/h.For the swing check valve,the research shows that when the valve closing time is 2s and the valve closing angle reaches 90~o,a negative damping spring torque is added to reduce the water hammer generated when the main circuit check valve is closed.