Evaluation of PWM solenoid valves to manipulate hollow cone nozzles operated at high pressures and frequencies

Abstract

<b><sc>Abstract.</sc></b> Hollow-cone nozzles coupled with pulse width modulated (PWM) solenoid valves have been used in orchard sprayers to perform variable rate applications. With current PWM valves, however, the nozzle flowrate modulation speed is limited at 10 Hz and the maximum nozzle operating pressure is at 690 kPa. In this research, twelve industrial-graded PWM valves were evaluated for their potential to achieve precision variable-rate functions with faster nozzle activation and higher operating pressure. Frequencies of PWM signals to activate the solenoid valves ranged from 5 to 50 Hz at 5 Hz intervals and duty cycles ranging from 10% to 100% with 10% intervals. A disc-core hollow cone nozzle was used to connect with each valve and operated at 1380 kPa to produce variable flow rates for the tests. Pressures at upstream and downstream solenoid valves were recorded and analyzed to determine the maximum duty cycle ranges and maximum PWM frequency. This information was then used to determine the maximum variable flow rate ranges of the nozzle manipulated with the specific PWM valve. Test results showed there were significant differences in flow rate modulations among the 12 PWM valves due to their design differences. The valves with the greatest modulation capability could manipulate nozzle flow rates at frequencies up to 30 Hz with duty cycles ranging from 20% to 70% and at frequencies up to 40 Hz with duty cycles ranging from 30% to 70%. Therefore, integrating this PWM valve into the variable-rate sprayers could increase the nozzle flowrate modulation speed by three to four times so that the variable-rate accuracy would be potentially increased by three to four times.