Spray Outputs from a Variable-Rate Sprayer Manipulated with PWM Solenoid Valves

Abstract

Abstract. Pressure fluctuations from air-assisted orchard sprayers can cause nozzles to discharge inaccurate flow rates during variable-rate spray applications. Variations in total flow rate discharged from 40 nozzles, each coupled with a pulse-width-modulated (PWM) solenoid valve, were determined for a variable-rate air-assisted sprayer. Variables for the total flow rate measurements were number of active nozzles ranging from 1 to 40 and PWM duty cycle ranging from 10% to 100%. Experiments were conducted under conditions with and without operating pressure adjustments. Under the no-pressure-adjustment condition, the operating pressure in the spray line was not adjusted for compensation when either the number of active nozzles or PWM duty cycle was changed. Under the pressure-adjustment condition, the operating pressure was adjusted to retain at 242 kPa. The total flow rate increased as duty cycle and/or number of active nozzles increased under both pressure conditions. However, the operating pressure in the spray line dropped considerably as either the number of active nozzles or duty cycle increased under the no-pressure-adjustment condition, resulting in significant lower total flow rates compared to the pressure-adjustment condition. The differences in total flow rates between the two pressure conditions increased as duty cycle and number of active nozzles increased. To improve future intelligent sprayer accuracy, two-variable regression equations were established to predict and control total flow rates with different duty cycles and numbers of active nozzles operated simultaneously. Keywords: Flow control, Flow rate, Hydraulic nozzle, Pesticide, Precision sprayer.