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

Authors: CAMPOS, JAVIER - The Ohio State University; Zhu, Heping; Jeon, Hongyoung; SALCEDO, RAMON - Technical University Of Catalonia; OZKAN, ERDAL - The Ohio State University; GIL, EMILIO - Technical University Of Catalonia

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2023
Publication Date: 4/28/2023
Citation: Campos, J., Zhu, H., Jeon, H., Salcedo, R., Ozkan, E., Gil, E. 2023. Assessment of PWM solenoid valves to manipulate hollow-cone nozzles with different modulation frequencies. Applied Engineering in Agriculture. 39(2): 235-244. https://doi.org/10.13031/aea.15415.
DOI: https://doi.org/10.13031/aea.15415

Interpretive Summary: Variable-rate pulsation valves have been successfully used in intelligent orchard sprayers equipped with laser scanning sensors to control spray outputs based on the plant canopy size, shape and foliage density. However, the valve activation speed is four times slower than the laser scanning speed, and the slow speed of the valves restricts full utilization of the laser sensor capability. In this research, twelve industrial-used flow-control pulsation valves were investigated to modulate agricultural-used hollow-cone nozzles at high operating pressures. The maximum modulation frequency and maximum functional duty cycle ranges were determined for these valves to activate the nozzles performing variable-rate actions. There were noticeable differences in activation responses to pulse modulations among the 12 valves due to their differences in designs. The investigations identified two appropriate valves that could achieve the laser scanning speed to manipulate open-close pulse actions of the hollow-cone nozzles. Integrating these valves into intelligent spray application systems could potentially increase the spray output modulation accuracy by four times compared with the commonly used low speed valves.

Technical Abstract: Integration of high-speed pulse with modulation (PWM) solenoid valves into variable-rate orchard sprayers is needed to increase spray output accuracy for sudden changes in plant canopy structure characteristics. Capability of twelve 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 disc-core hollow-cone 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 properly. 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 modulation frequency of 40 Hz. These two PWM valves performed the highest capability among the 12 valves to manipulate the hollow-cone nozzle, and they would be selected for further investigations on their flow rate modulation accuracy and droplet size distributions before they could be recommended for adaptation in precision variable-rate orchard sprayers.