Statistical Analysis of Non-Pressure-Compensating and Pressure-Compensating Drip Emitters
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abstract
Drip irrigation may need to be installed in situations in which there is not enough energy to operate the emitters under optimum performance conditions. This paper characterizes the head-discharge functional form of a pressure-compensated (PC) and non-pressurecompensating (NPC) drip emitter operating under low pressures. It also analyzes the statistical relationship between manufacturing and hydraulic variations of low-pressure operating emitters assuming that both are independent random variables. A hydraulic simulation methodology was implemented to predict the effect of emitter manufacturing and hydraulic variations on irrigation uniformity while working under a range of operating pressures. The manufacturing variation of PC and NPC emitters was evaluated with the Monte Carlo method for a single horizontal drip line with different pressure heads and different numbers of emitters evenly spaced. The coefficient of manufacturing variation (CV k ) observed in the laboratory was 9.2% for PC (Toro) emitters and 3.8% for NPC (T-tape) emitters. Laboratory test results showed that manufacturing and hydraulic factors were stochastic independent variables, and this independent relationship allowed the combination of statistics for estimating the coefficient of total variation. The manufacturing emitter variation has a considerable impact on lowquarter distribution uniformity (DU lq ), as the number of emitters in the drip line is increased. For instance, the DU lq of the PC (Toro) emitter decreased considerably from 1.0 to 0.82 compared with the NPC (T-tape) emitter, which varied from 0.943 to 0.939 when the length was increased from 60 to 200 emitters long drip line. The PC emitter started compensating at 6.16 m of hydraulic head. Therefore, this type of emitter is not recommended for low operating pressure systems. It is recommended to design low-pressure irrigation systems with the right emitter type and operating pressure to maximize performance. 2013 American Society of Civil Engineers.
