Assessment of pwm solenoid valves to manipulate hollow-cone nozzles with different modulation frequencies

Integration of high-speed pulse-width-modulation (PWM) solenoid valves into variable-rate orchard sprayers is needed to accurately regulate spray outputs for matching changes in plant canopy structure characteristics. Capability of 12 PWM valves to modulate hollow-cone nozzles for variable-rate applications was investigated with PWM frequencies of 5 to 50 Hz and duty cycles of 10% to 100%. The PWM valves were assembled on a laboratory spray system with a hollow -cone disc-core nozzle of 2.84 L min-1 flow capacity operated at 1380 kPa pressure. The upstream and downstream pressures on the PWM valves were recorded and analyzed to determine the maximum functional duty cycle ranges and maximum PWM frequency at which the PWM valves could manipulate the nozzle functionally. Test results showed that there were noticeable differences in the modulation capability among the 12 PWM valves due to their design differences. Two out of 12 valves were able to manipulate the hollow-cone nozzles with duty cycles ranging from 30% or 40% to 70% at the mod-ulation frequency of 40 Hz. These two PWM valves performed the highest capability among the 12 valves to manipulate the hollow-cone nozzle. As a result, these two valves would be selected for future investigations on their flow rate modulation accuracy and droplet size distributions before they could be recommended for adaptation in the variable-rate orchard sprayers.