Analysis And Protection Of Water Hammer At The End Of Closed Valve Of Pressurized Self-flowing Pipeline With Abnormal Gas

Gravity flow pipeline is built according to the topography,undulating and easy to collect gas.Serious water hammer accidents may occur when the flow rate is adjusted and the valve is suddenly closed.In order to ensure the safe and stable operation of the transmission and distribution network,this paper uses the method of combining experimental analysis and numerical simulation calculation to explore the water hammer and its protection method of the valve closing at the end of the gravity flow pipeline in the abnormal gas-bearing state.Firstly,an experimental platform is built to solve the problem of water hammer pressure in the condition of no gas and abnormal gas.Based on the principle of water hammer calculation and the related boundary conditions,the calculation model of water hammer is constructed.The experimental results show that the maximum water hammer pressure and pressure ratio of the pipeline system with gas is 1.98 times of that of the pipeline system without gas,which indicates that the abnormal operation of the pipeline system with gas will produce greater water hammer pressure and pressure ratio.In the case of the same proportion of air bag volume,the initial flow rate is 1.24 m / s,1.59 m / s,When 1.77 m / s,the water hammer pressure is 54.49 m,64.02 m and 88.26 m respectively,which means that the water hammer pressure produced by closing the valve at the end has a positive correlation with the initial velocity of the pipeline system.At the same flow rate,the correlation curve between the ratio of water hammer pressure and the proportion of the volume of the gasbag is an open-down parabola.The volume of airbag needed for maximum water hammer pressure is different in different system flow rates.The deviation between the model validation results and the experimental data is within the controllable range,which provides a reliable experimental basis and calculation method for water hammer calculation and analysis.Secondly,the water hammer protection experiment is carried out on the pipeline system,and the water hammer protection performance of the high proportion pressure reducing valve with spray hole is explored.No matter whether the pipeline system contains gas or not,the nozzle heave type high proportion pressure reducing valve has good water hammer protection effect.When the pipeline system is in different initial pressure and different proportion of the volume of the air bag,there is no water hammer pressure rise in the process of closing the terminal valve.The simulation results are consistent with the measured data,which provides an effective protection method for water hammer calculation.Finally,the water hammer pressure of gravity flow tree pipe network under the condition of no gas and abnormal gas is simulated.The main pipe with a large flow rate can reduce the water hammer pressure when the valve at the end of the branch pipe is closed,and when the valve at the end of the main pipe is closed alone,the water hammer pressure will be increased.When the main pipe and the branch pipe near the end of the pipe close the valve at the same time,the influence of water hammer pressure on the main pipe is greater.When the valve at the end of the pipeline system is closed at the same time,the maximum water hammer pressure in the main pipe can reach 440.77 m,which is 1.78 times of that in the case of no gas,and serious water hammer accident will occur in the pipeline.The analysis of water hammer protection under the most unfavorable working conditions of the project shows that when the main pipe and each branch pipe are installed with the nozzle heave type high proportion pressure reducing valve,there is no overpressure or negative pressure phenomenon in the whole pipeline system,which meets the water hammer protection requirements of the pipeline system.