Study On Valve-closure Water Hammer And Terminal Pool Flow Control In Water Supply Network

In China’s water supply network,there are many storage facilities,such as water pools,water tanks,so the matching valves are essential for the operation of water pools and tanks.In the process of pipe network operation,various pipe network accidents are often caused by improper operation of the valve.However,in the pressurized water supply network,the previous scholars paid more attention to the water hammer hazard caused by the sudden stop of the pump.Few people have studied the water hammer caused by the sudden closing of the end valve.Therefore,based on the experiments,a simulation program for gas-liquid two-phase flow hammer is compiled.Taking a tree water supply network in a county as an example,a simulation study is carried out on the water hammer of closing valve with and without gas in pipeline.Firstly,we built a pressure flow experimental platform with branch pipe to simulate small pressurized water supply network,and in order to ensure the reliability of the simulation results,the characteristic curve of the valve was measured by the experimental system.In the experiments,the pipe flow velocity is 1.7m/s and 2.0m/s,and the gas volume is 10m~3/h,the pressure rise caused by the closing of the two valves was tested under the condition of gas and no gas respectively.The experimental results show that the maximum pressure rise caused by the closing of ordinary floating ball valve is 2 times higher than the steady-state pressure,and there’s almost no pressure rise occurs when the non-frequency valve is closed;Then,the back drain valves of the water tank were opened for 30s and 60s respectively to simulate the user’s water use process,and the flow control performance of the two valves was tested by observing the valve action times and the flow changes in the pipeline during the drainage process.In the30s of drainage process,the ordinary floating ball valve acted twice,and the non-frequency valve only acted once,the experimental results show that the non-frequency valve is effective in controlling flow and stabilizing pressure in the terminal pool.Secondly,the water hammer of closing valve at the end of branch pipe was studied in the experimental pipeline,which was realized by quickly closing the butterfly valve in front of the water tank.The valve closing experiments with and without gas are conducted with flow rate of 1.7 m/s and 2.0m/s,valve closing time of 1 s and 1.5s respectively,and gas volume of 10m~3/h.When there is no gas,the maximum pressure rise value of the experiment is 3.3times higher than the steady-state pressure,On the contrary,the maximum pressure rise is about4.8 times higher than the steady-state pressure.According to the basic theory of water hammer,reasonable assumptions and simplifications are made for the two-phase flow in the pipeline.A calculation model for the transition state process of valve-closing water hammer was established,and the pump-stopping and valve-closing water hammer of the test pipe network were simulated and calculated.After comparing with the experiment results,the maximum deviation was 5.75%.The results show that the model is relatively reliable and suitable for the calculation and analysis in this article.Finally,the simulation calculation of water hammer in different combinations is carried out for an engineering example.The results show that closing the valve at the end of the pipe will affect the branch pipe and the adjacent nodes of the pipe.When the gas content of the pipe is about 8%,the pressure oscillation caused by closing the valve is more obvious.When all the valves are closed at the same time,the water hammer wave generated in the pipe is the most obvious,and the maximum pressure rise value is about 4.2 times higher than the steady-state pressure.The overall pressure rise caused by valve closing is slightly less than that caused by water hammer when the pump stops,but its harmfulness can not be ignored.The protective measures of"exhaust valve+tank-type bidirectional regulating towers+non-frequency valve"were adopted for water hammer protection calculations,it can be obtained that the pressure increase value of the pipeline network is in the normal range,which can ensure the safe operation of the pipeline.