A Laboratory System for Nozzle Spray Analysis

Droplet spray spectrum is one of the most important factors affecting the biological efficacy of a phytosanitary treatment and water sensitive papers (WSP) are one of the most widely used tools to asses spray coverage. Aim of this study is to present a low cost laboratory test bench, suitably designed to analyse nozzle sprays according to the procedure established by ISO 5682-1 and to allow studying the correlation between spray features and WSP surface coverage. The test bench consists of a transportable trolley carrying a 70 L tank, a diaphragm pump driven by an electric motor, and a spray boom applied to a mobile support that moves along two slides placed above and parallel to the plane of the trolley, in such a way the distance between target and nozzle is 0.5 m. According to the procedure established by ISO 5682-1, the nozzle under test sprays a mixture with water-soluble dye (Poinceau Red) above Petri dishes containing silicon oil. The images of the drops trapped into the oil are acquired by using a high resolution (24 Mpixel) DSLR camera and then analysed with image analysis software. Moreover, spraying at the same time Petri dishes and WSPs, the data coming from the drops inside the Petri dishes can be correlated to those coming from the image analysis of WSPs. To better asses the WSP behaviour, this paper also reports the results of some simulations of WSPs when sprayed with drops of assigned drop size distribution (log-normal) and volume median diameter ranging from 125 µm (fine spray) to 475 µm (coarse spray). The simulations showed that the overlap between stains is independent from spray features and that the unitary deposit (µL cm−2) is highly correlated to the percentage of covered surface by means of second order equations whose coefficients depends on volume median diameter of drops.