## 3 Results and Analyses  
Figure 3 shows the formation of airflow resistance through the dust-free filter material. Using the functions indicated in the diagram, the resistance value of the clean filter material for a new bag \(\Delta\)p\({}_{0}\) was calculated based on formulas no. 1 and 2 for a specific filtration speed of 0.0405 m\(\cdot\)s\({}^{-1}\), which was used in the test filtration processes. This resistance was 41.448 Pa. On the other hand, the value of the K\({}_{0}\) coefficient, which is the slope of the equation for the appropriate working time of the bag, was read from the graph for the bag that was not used before and was 1023.4 Pa\(\cdot\)s\(\cdot\)m\({}^{-1}\), while for the load used for 382 days, it is as much as 2618.9 Pa\(\cdot\)s\(\cdot\)m\({}^{-1}\). Analyzing the above graph (Figure 3), it can be stated that with the increasing service life of the bags, the value of the resistance to the flow of clean air through the non-woven fabric increases. This is due to the growing penetration of wood dust inside the filter material. Comparing the obtained results, the resistance values \(\Delta\)p\({}_{0}\), and the K\({}_{0}\) coefficient, we note that for bags from the same production line, they are lower than those obtained when testing the nonwoven fabric made of material B, for which the results are described in a previous paper [28], which shows that the resistance values are dependent on the type of non-woven fabric used. The next test stage was to test the resistance during the filtration of air dusted with standard wood dust. As the duration of the test increased, the flow resistance increased. At the beginning of the study, there was a significant increase in resistance. After some time, the increase in resistance slowed down, showing slight increases at the end of the test process. The formation of the resistance for filter bags operating at different times in an industrial installation is shown in Figure 4.  
Figure 4: Airflow resistance through the filter fleece before the regeneration impulse for the bags used in the tests. Service life of 0, 85, 146 and 275, and 382 days. Figure 3: Pressure drop across clean filter media from narrow-surface treatment line—service life of the bags: 0, 85, 146, 275, and 382 days. When analyzing the data presented in the diagram, it is easy to note the increasing value of the filtration resistance depending on the time the bags are used in the filtering dust collector. Comparing the obtained results with previous studies [28], for a similar period of operation (272 days for material B and 275 days for material A), we can see that material A obtained filtration resistance approximately 20% higher than material B, with 123.4 Pa for material A and 101.52 Pa for material B. Similar characteristics of changes in filtration resistance were obtained by [PERSON], [PERSON], and [PERSON] [33] while examining PE and PTFE nonwovens coated with a membrane. They tested five types of nonwovens in terms of filtration resistance depending on the porosity of the nonwoven fabric and the thickness of the fiber. The values of the total resistance \(\Delta\)p\({}_{\text{C}}\) for the particular periods of use of the bags in the industrial installation after the end of the experiment covering 50 filtration cycles on the experimental stand were determined using the regression equations. The equations and the values of \(\Delta\)p\({}_{\text{C}}\) are presented in Table 5 and are compared with the values obtained in the tests of bags made of material B [28]. Based on the obtained results and using formula (6), the value of the K\({}_{2}\) dust resistance coefficient for material A was calculated. The K\({}_{2}\) coefficient for material B was calculated earlier [28]. For clarity, Table 6 also presents the results obtained in [28] for material B from the same dust extraction installation. The results shown in Figure 5 indicate different shapes of the K\({}_{2}\) coefficient under the same conditions of use, depending on the type of filter material used.