The distribution characteristic of emitters′ flow coefficient is analyzed. When flow coefficient complies with normal distribution, the probability of flow coefficient fluctuating at ±3 times standard deviations is 9973％ (approximating 100％). Thus, the minimum flow coefficient is average flow coefficient minus 3 times standard deviation and the maximum flow coefficient is average flow coefficient plus 3 times standard deviation. Based on the above analysis, a comprehensive flow variation rate calculation formula, taking hydraulic variation, manufacture variation and microterrain variation into consideration, is presented. Then, with emitter manufacturing variation coefficient, flow exponent, pressure difference and average field roughness height as influential factors, flow variation rate and lateral cost sensitivity were analyzed. The results show that emitter manufacturing variation coefficient is the most influential factor, followed by flow exponent and pressure difference. The lateral cost increases dramatically when manufacturing variation coefficient is larger than 004. In designing, emitters with minimal manufacture variation and minimal flow exponent should be elected. For normal drip irrigation systems, when the emitter′s waterdrop is larger than 10m, the effects of local height differences in fields on flow variation can be ignored.
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