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| Variation of vertical soil water content at emitter in different fertilizer concentrations |
| BAI Mianmian, WANG Fujun, LEI Cheng, WANG Ling, LIU Bangchao |
| 1.Branch of Water Resources, Shaanxi Province Institute of Water Resources and Electric Power Investigation and Design, Xi′an, Shaanxi 710001,China; 2. Beijing Engineering Research Center of Safety and Energy, China Agricultural University, Beijing 100083, China |
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Abstract In order to study the role of a bypass valve during maintenance process of a long water transport pipelines with gravity flow, a computational model of bypass valve is built based on method of characteristics. In a large water transport pipeline with gravity flow, hydraulic transient processes with and without bypass valve are analyzed. It is found that the maximum pressure head decreases and the minimum pressure head increases in the pipeline with bypass valve compared with the pipeline without bypass valve. When the closure time of service valve is fixed, the longer the closure time of bypass valve, the smaller the maximum pressure head, and the milder the pressure surge. When the closure time of bypass valve is fixed, the closure time of service valve has a little effect on pressure surge but a greater effect on the initial time of pressure surge. Moreover, it is shown that the degree of protection of the bypass valve depends on section in the pipeline, and the surge protection is more significant in the starting section and ending section of the pipeline.
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Received: 20 April 2017
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