Effect of agricultural sprayer flow control hardware on nozzle response

Modern rate controllers along with technologies such as automatic section control (ASC) can improve in-field input use efficiency while preventing detrimental effect of unwanted spray application in areas such as grassed waterways or other environmental structures. However, the understanding of product (liquid) dynamics within the boom plumbing on off-rate and application uniformity during rate control and ASC actuation is limited. Therefore, a study was conducted to compare nozzle flow stability and uniformity across the boom when using two boom (2-way and metered 3-way) and two flow regulating (butterfly and ball) valves combinations. Tests were conducted using a 18.3 m sprayer with boom-section control. Pressure transducers were mounted at 1) the boom manifold, 2) randomly at 12 nozzle bodies across the spray boom and, 3) upstream and downstream of the flow regulating valve. Effective system flow rate was measured using two flow meter(s), one located upstream of the boom control valves (2-way or metered 3-way) and another mounted to measure the tank return flow for the metered 3-way boom valve. Measured nozzle pressure was converted to nozzle flow using the manufacturer's pressure-flow data. Results indicated that the 2-way boom valve response was significantly different as compared to metered 3-way valve. Differences were also indicated by the damping ratios when exiting (under-damped) and reentering (over-damped) spray zones. For the metered 3-way boom valve configuration, the nozzle flow settled faster (0.1 to 4.2 s) generating negligible off-rate errors whereas the 2-way boom valve configuration took up to 34.3 s to settle with off-rate errors between 3.3% and 11.5%. The delayed nozzle flow settling times were associated with pressure settling (0.7 to 31.4 s) downstream of the regulating valve for the 2-way configuration. Ground speed and point row angle impacted nozzle flow settling times and off-rate errors. The increase in ground speed and point row angle increased nozzle flow settling time for the 2-way valve setup, except that acceleration decreased settling times when exiting spray zones. The delayed response contributed to off-rate time which decreased as the sprayer accelerated and point row angle decreased for both the 2-way (1.7 s to 19.3 s) and metered 3-way (2.1 to 4.4 s) boom valves setups. Further, the varied nozzle flow settling times using the butterfly (1.0 to 23.7 s) and fast (0.4 to 15.6 s) regulating valves indicated that one valve calibration number (VCN) may not apply to all sprayer configurations and field operations.