For hydraulic design of drip irrigation lateral to be improved, the minor head loss caused from online emitters in drip irrigation laterals was explored experimentally. Based on the experimental results, the minor head loss coefficient ξ and the ratio of the minor head loss over the frictional head loss, hj/hf, were correlated to Reynolds number and emitter spacing for different types of emitter. It was shown that hj/hf is considerably dependent on type of emitter and emitter spacing. At the same emitter spacing, hj/hf caused from online labyrinth channel emitters is greater than that from pressure compensating emitters; for the same type of emitters, however, hj/hf is inversely proportional to emitter spacing. Importantly, all the hj/hf values are larger than those specified in the Technical Standard of MicroIrrigation Project (SL-103-95). According to the standard, the minor head loss is about (0.1-0.2)% of the total frictional head loss; obviously the total head loss will be underestimated by this. Further, the minor head loss coefficient ξ are related to the type of emitter, Reynolds number and emitter spacing. For labyrinth channel emitters the coefficient is higher than 0.6; however, for compensating pressure emitters, it is ranged in 0.3-0.5. The coefficient increases with decreasing emitter spacing, and declines with increasing Reynolds number. An empirical formula for the coefficient was proposed by regression.
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