## 1 Introduction  
Spraying liquid is currently a technically and technologically important process that has found application both on conventional and ecological farms as well as in industries producing food, pharmaceutical drugs, in steelworks, power plants, rolling stock, coatings, and in other sectors of the economy [1]. A flat fan spray nozzle serves the purpose of spraying onto a surface or an object moving in a transverse direction with respect to the direction of the jet, a typical example being the nozzles in a car washing tunnel. Farmers have always sought to facilitate their day-to-day labour. Already in the 19 th century, when chemical preparations had begun to be used in agriculture, one of the devices which allowed crop cultivation, gardening, and fruit growing to flourish was the sprayer. Currently, it is argued that the maintenance of rich agricultural landscape, low consumption of plant protection agents, and efficiently functioning control systems are a good foundation for the systematic and sustainable development of rural environments [2]. The effectiveness of each agrochemical treatment results primarily from the cultivation conducted and soil conditions, on top of which is the purposefulness of the treatment affecting the soil, plant, or aprophage, from the preparation and equipment employed, as well as the precision of its performance. The precision of the performance is primarily the outcome of the working pressure and speed of passage that determine the quantity of the preparation dose applied. Each of these factors determines the effectiveness of field works. Hence the heterogeneity and predictability of the distribution of sprayed liquid are the principal features of sprayers. The quality of agricultural spraying depends, to a large extent, on the uniformity of the sprayed liquid dispersal over the sprayed surface. Presently, in field cultivation, flat fan nozzles, which wear out during their operation, are used the most frequently [3; 4]. A worn-out nozzle causes the quantity of the outflowing liquid to increase, thus disrupting the uniformity of liquid distribution. The current Directive of the European Parliament and Council 2009/128 EC on the sustainable use of pesticides in agriculture contains guidelines concerning, among others, tests of spraying nozzles in agricultural sprayers [5]; the parameter being subject to tests in field sprayers regarding the uniformity of the working liquid distribution over the sprayed surface. The ISO standard regarding the examination of used agricultural sprayers stipulates that the coefficient of variation (\(CV\)) cannot exceed 10% [6]. Specialist devices with a grooved table are used for measuring the uniformity of spray distribution [2; 6; 7]. The degree of nozzle wear impacts the obtained measurement of the coefficient \(CV\)[8]. During periodic approval inspections of agricultural sprayers, the value of this coefficient determines whether a sprayer is approved for use. The technical condition of the nozzles installed on the boom of the sprayer also affects the quality of spraying and the application of liquid [9]. This uniform spraying of plants mainly determines the effectiveness and quality of agricultural spraying, reduces the quantity of pesticides used in agricultural production, and affects the safety of the environment. The development of nozzle design and the positioning on the sprayer boom significantly affect the uniformity of the sprayed liquid falling onto the sprayed surface. Flat fan nozzles were initially made of metal, but their durability was not satisfactory. A rapid development of new designs has been observed since the emergence of the possibility of manufacturing nozzles from plastic. The current standards for ground-level spraying systems in field cultivation, used for spraying the entire surface, assume that 24 single flat fan nozzles are to be placed on the linear boom of a field sprayer with an operational width of 12 m with 0.5 m spacing (Figure 1). The distance between the nozzles does not change.