Design and Testing of a PLC-Controlled Pressure Stabilization System for Targeted Spraying on Heading Vegetables

In agricultural plant protection, pressure fluctuations during targeted spraying are a key factor affecting spray quality. To address the issue of pressure fluctuations in the system pipeline caused by the inconsistent opening and closing of nozzles during targeted spraying, this study proposes a pressure-stabilizing device based on programmable logic control (PLC). To verify the feasibility of the system, experimental tests were conducted to assess pressure fluctuations, spraying volume, and droplet characteristics. The tests were performed at three different pressure settings: 0.3 MPa, 0.4 MPa, and 0.5 MPa, and the effects of opening and closing between one and five nozzles on system performance were examined. The results revealed that as the Δn (defined as the change in nozzle number) increased during target application, the pressure fluctuation also increased, reaching up to −0.008 MPa. Conversely, as the number of closed nozzles increased, the pressure fluctuation grew, reaching up to +0.006 MPa. Due to the frequent opening and closing of the solenoid valve, pressure fluctuations occur in the pipeline, with the duration of these fluctuations closely matching the solenoid valve’s response time of 60 ms. A model correlating the Δn with the nozzle flow rate was developed, showing a strong fit. This indicates a significant correlation between the Δn and flow rate, while the nozzle flow rate is minimally affected by pressure fluctuations in the system. An analysis using a laser particle size analyzer revealed that the droplet characteristics of the targeted spraying exhibited good stability. In conclusion, the system demonstrated excellent spraying performance during targeted spraying operations. The results of this study offer valuable insights for the design and optimization of targeted spraying and provide support for advancements in precision spraying.