Air-pinch PWM valve to regulate flow rate of hollow-cone nozzles for variable-rate sprayers

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

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2023
Publication Date: 10/31/2023
Citation: Campos, J., Zhu, H., Jeon, H., Salcedo, R., Ozkan, E., Roman, C., Gil, E. 2023. Air-pinch PWM valve to regulate flow rate of hollow-cone nozzles for variable-rate sprayers. Journal of the ASABE. 66(5): 1317–1329. https://doi.org/10.13031/ja.15601.
DOI: https://doi.org/10.13031/ja.15601

Interpretive Summary: Pesticide sprayers are commonly used to achieve efficient and effective crop protection for securing high food quality and quantity. Electric pulse width modulation solenoid valves are the critical component for the sprayers to provide precision variable rate applications. However, these valves pose a potential problem that they cannot shutoff completely if sprayers are not rinsed thoroughly after applying adhesive additives or physically incompatible powder pesticides. In this research, an air-pinch valve that separated the chemical liquid from the valve chamber was investigated as an alternative to the electric valve. Tests included the modulation accuracy of flow rates and droplet size distributions discharged from various hollow-cone nozzles controlled with the air-pinch valve. A conventional electric valve was also used for comparison. Test results showed the air-pinch and electric valves performed equivalent accuracy in flow rate modulations for hollow-cone nozzles operated at different pressures. Similarly, droplet size distributions and classifications from the hollow-cone nozzles regulated with both valves were also comparable across the flow rate modulation range from 20% to 100%. Therefore, the air-pinch valve could be an alternative to conventional electric valves by isolating the valve actuation components from contacting chemicals, thus preventing the potential valve shutoff problem and further improving the accuracy and reliability of precision variable rate sprayers.

Technical Abstract: Electric pulse width modulation (PWM) solenoid valves are commonly used to regulate nozzle flow rates to achieve precision variable-rate spray applications. However, some pesticide formulations such as wettable powders and adhesive additives can potentially cause a problem that the valve cannot completely shut off during flow rate modulation if spray lines are not cleaned thoroughly after spray applications. An air-pinch PWM valve was evaluated to modulate flow rates of hollow-cone nozzles to prevent this malfunction. With this valve, spray mixtures only passed through a flexible tube to avoid chemicals directly contacting the moving components inside the valve chamber. The flow rate modulation was performed by pinching the tube back and forth with air-pilot PWM actions. Evaluations included the flow rate modulation capability along with droplet size distributions from three disc-core hollow-cone nozzles coupled with the PWM pinch valve and compared with a conventional electric PWM valve. Both air-pinch and conventional electric PWM valves performed comparably in the flow rate modulation accuracy and droplet size distribution for hollow-cone nozzles operated at 414 and 827 kPa pressures across the duty cycles (DUCs) ranging from 10% to 100%, except for the air-pinch valve that could not activate at 10% DUC. Flow rates of nozzles modulated with both PWM valves at all DUCs were 5.3% greater in average than the target flow rates while the flow rates were similar at 90% and 100% DUCs. Droplet size classifications based on the ASABE Standard S-572.3 were generally consistent across DUCs ranging from 20% to 100% for the same nozzle and pressure with the air-pinch PWM valve and from 10% to 100% with the conventional electric PWM valve. The consistency of droplet sizes across DUCs and accuracy of flow rate modulations demonstrated the potential advantage of using the air-pinch PWM solenoid valve as an alternative for precision variable-rate sprayers to accurately apply different chemicals.