Zhu Delan1, Wu Pute1,2, Li Lanbin1, Zhang Chen1, Wang Jian1
（1.College of Resources and Environment，Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, China; 2.National Engineering Center for Irrigation Water Savings，Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, China）
In order to find design method of gravity-fed manifold subunit, the emitters discharge variation rate caused by hydraulic variation, emitter manufacturing variation and micro-topography variation were used as the criteria of irrigation uniformity. Then, the emitter discharge variation rate caused by hydraulic factor, the pressure head variation, and the maximum pressure head for different pressure sections were determined. By analyzing water pressure head relationship of different pressure units, the distribution coefficient of manifold pressure head variation for different pressure area was calculated, and the manifold subunit design was divided into independent processes for laterals and manifold. In the manifold design, a two-stage optimal design method was used. The size of each of the pressure sections was determined according to the pressure head distribution along the manifold. The different emitter types were chosen according to the nominal design pressure which best matches the available pressure at the entrance of each lateral. The design procedure can be applied in a spreadsheet application on a personal computer.
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