# Evaluation of Different Internal Designs of Hydraulic Nozzles under an Accelerated Wear Test
## 3 Results  
To determine whether a certain nozzle is worn out, the wear rate for the nozzle must be less than 10% according to the threshold specified by ISO 16122-2 [23]. If the measured wear rate of the nozzle exceeds this threshold, then it needs to be replaced by the operator or by the sprayer inspector during periodic inspection. Table 2 shows the wear rate (%) for the three types of nozzles; they did not exceed the 10% threshold during the whole test. The highest wear rate was registered for the DG nozzle after 40 h of the accelerated wear test, and it was 9.0%. The TTj60 nozzle had a negative value of wear rate after 60 h of wear; this was because the measured flow rate at this time was less than the nominal value. The reason for this phenomenon is not yet known. The flow rates for the TT, TTj60, and DG nozzles during the wear test intervals as measured using 3.0 bar pressure, are presented in Figure 4. The TT and DG nozzles showed a progressive increase in flow rate during the first 50 h of wear, while the TTj60 nozzle showed a progressive decrease in flow rate. Regression analysis was conducted considering the hours of wear as a predictor and the flow rate as the response. Several models' orders were investigated for each nozzle type considering the coefficient of determination (R\({}^{2}\)) of the model as a criterion to determine the best model. Three models were selected to predict the flow rate based on the hours of wear--one model for each type of nozzle. A 3 rd-order model was obtained for the DG nozzle type, where R\({}^{2}\) was 0.54, and a 5 th-order model for the TT nozzle type, where R\({}^{2}\) was 0.76. A 2 nd-order model for the TTj60 nozzle type had a low R\({}^{2}\) (0.31). These models did not show significant prediction as shown in Figure 4.  
After analysis of the changes in nozzle structure with visual methods (Figure 5), it was not possible to notice changes in the dimensions of the nozzle orifice. It is worth \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Nozzle**} & \multicolumn{8}{c}{**Hours of Wear, h**} \\ \cline{2-10}  & **10** & **20** & **30** & **40** & **50** & **60** & **70** & **80** & **90** & **100** \\ \cline{2-10}  & \multicolumn{8}{c}{**Wear Rate, \%**} \\ \hline TT & 3.2 & 4.2 & 5.2 & 6.2 & 5.8 & 5.6 & 6.2 & 6.2 & 6.6 & 7.4 \\ TTj60 & 2.1 & 0.9 & 1.0 & 0.5 & 0.1 & \(-\)0.4 & 0.4 & 0.7 & 0.7 & 0.5 \\ DG & 3.7 & 4.9 & 7.1 & 9.0 & 7.8 & 6.5 & 7.8 & 6.7 & 7.3 & 8.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The wear rate (%) during the different wear periods for the three types of nozzles. Figure 4: Flow rate at different wear intervals for the TT, TTj60, and DG nozzles. menting that these photos were taken for the pre-orifice from inside the nozzle body. It was not possible to take such photos for the final orifice from outside because of the geometry of these nozzles, especially the TT and TTj60 nozzles where the final orifice from outside is almost hidden. Further investigation was done by measuring the area and diameter of the nozzle orifice by taking photos of the nozzle orifice (Table 3). The dimensions (area and diameter) of the TT and DG nozzles increased after finishing the accelerated wear test, whereas there were no changes in the area and diameter of the TTj60 nozzle orifice after finishing the accelerated wear test. The obtained results were probably caused by two factors. Firstly, the effect of the pre-orifice nozzle design may reduce the pressure inside the second chamber (between the pre-orifice and final orifice). This reduction in liquid pressure reduced the flow energy of this liquid and then could affect the wear process of the nozzle orifice. Secondly, the TTj60 nozzle has two final exits; this probably reduced the liquid pressure further and reduced its effect compared with the TT and DG nozzles, which both have  
Figure 5: Photographs of the nozzle pre-orifice (from inside the nozzle body) before (New) and after the accelerated wear test (Worn): (**a**) DG nozzle, (**b**) TT nozzle, (**c**) TTj60 nozzle.