## 4 Discussion  
During the experimental tests, a threaded drive was used to determine the position of the control piston \(h\), while the target position was determined by moving the differential tract in conjunction with the pusher (guide). The manual control of the control piston position in the experimental tests presented in the above article required an additional tension spring 17 (Figure 1), which enabled the precise control of the opening of both supply paths. Without a tension spring, the control piston was incorrectly positioned inside the valve working chamber due to friction between the seal and the valve body walls. During the experimental tests, the zero position of the valve was adjusted by observing the pressure in the measuring tank after opening the control solenoid valve. The control piston position was adjusted independently for both paths before each measurement. The adopted method of regulating the degree of opening was the least invasive, with no direct effect on the internal volume of the valve. A comparison of the static flow characteristics determined by regression lines fitted with a second- and third-degree polynomial function (Figures 15 and 16) shows small differences between the two methods used, while the determined values of MAE and MAPE provide more accurate data. Analyzing the values of these indicators for the main supply tract during braking based on Table 1 shows that the value of the relative error ranged from 1 to 11%. In the entire measurement range, this translates into a discrepancy of 5.88% between the two measurement methods. Considering the same supply tract during release of braking, these discrepancies amounted to 10-25%, which, across the entire measurement range, equated to an average discrepancy of 17.25%. For the additional tract, the relative error values during braking were in the range of 2-20%, giving an average of 9.4%, while during debraking they were in the range of 0-14%, giving an average relative error value of 5.2%. It should be noted that the geometry of the additional tract does not allow for static characteristics close to linear. This is because, with an opening greater than 2 mm, the output flux is reduced, which limits the acceleration effect. This effect was observed in both the experimental and numerical approaches. The small sample size, resulting from the limited number of repetitions of experimental tests and the large capacities of the supplying and measuring tanks, contributed to the use of MAPE and MAE indicators, which, despite their limitations, made it possible to determine the discrepancies between the experimental and numerical approaches. The adopted simplifications in numerical modelling and the lack of simplifications related to the shape of seals (radius of fillets) in the 3D model had little influence on the quality of the numerical model in Figure 10, determined by the evaluation indices in Ansys Fluent. Compared to the previous numerical studies conducted in a different environment, there are small differences between the numerical methods, while greater possibilities for model discretization; in addition, the possibility of dynamic modelling resulted in focusing on the further use of the Ansys Fluent software only. The analytical and numerical flow models used required certain simplifications, including adiabatic flow (constant value of inlet and outlet temperature), which excludes the influence of temperature on the results obtained. This is due to the static approach, in which the valve design made it impossible to record changes in the compressed air temperature and the inner wall body without significantly interfering with the structure. Further dynamic studies of the numerical model will take into account the differential (correction) effect of temperature on the valve body and the compressed air near the walls and moving elements. Further research on the presented conceptual solution of the brake valve with a correction system will focus on dynamic experimental studies.