## 3 Results and Discussion
### Relationship between the Position of the Fine Inspection Port and Detection Characteristics  
This section discusses the study of the detection characteristics of the helium mass spectrometer leak detector when the fine inspection port is at different positions of the turbine stage and determines the position of the fine inspection port by integrating the actual use requirements of the leak detector. When analyzing the pumping performance of multiport hybrid molecular pumps, the model for the calculation of the turbine-stage combined blade row was used first to obtain the pumping parameters \(S_{2}\), \(S_{3}\), and \(K\) when  
Figure 6: Influence of the turbine blade structure parameters on the inspection performance: (**a**) blade inclination on \(K_{1}/K_{2}\) and \(S\), (**b**) blade number on \(K_{1}/K_{2}\) and \(S\), (**c**) blade height on \(K_{1}/K_{2}\) and \(S\). the fine inspection port was at different positions. Then, the relationship between the location of the fine inspection port and the detection characteristics was studied through the calculation model of the fine inspection condition. To analyze the influence of the position of the fine inspection port on the pumping characteristics of the multiport hybrid molecular pump, fine inspection ports were set between adjacent dynamic and static blades. The mean integral method was used to calculate the pumping parameters \(S_{2}\), \(S_{3}\), and \(K\) of the turbine blades at 11 fine inspection port positions. The calculation results are shown in Table 4.  
2.1 Relationship between the Position of the Fine Inspection Port and the Working Pressure of the Inspected Part  
Before the helium mass spectrometer leak detector starts, the tested parts must be placed under a vacuum, and the pressure in the mass spectrometer chamber must be reduced below the allowable pressure (calculated as 0.01 Pa in this paper). At this point, air is the only gas entering the vacuum system of the leak detector. The mass spectrometer chamber pressure \(p_{2}\) was calculated when the working pressure \(p_{1}\) of the tested part was 10 Pa, 5 Pa, 1 Pa, and 0.1 Pa and the fine inspection port was at different positions. The calculation results are shown in Figure 7.  
As shown in Figure 7, the pressure in the mass spectrometer chamber gradually decreased as the opening position moved from the 1 st- to the 12 th-stage blade row. According to the requirement that the allowable pressure \(p_{2}\) in the mass spectrometer room should be less than 0.01 Pa, when \(p_{1}\) = 10 Pa, the fine inspection port should be behind the 8 th-stage blade row. When the working pressure is \(p_{1}\) = 0.1 Pa, the fine inspection port can be behind the 3 rd-stage blade row. After the pressure of the mass spectrometer chamber reached the working pressure requirements, the gas entering the vacuum system was a mixture of air and helium. The model for the calculation of the inspection condition was applied to calculate the return \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Position** & **1-2** & **2-3** & **3-4** & **4-5** & **5-6** & **6-7** & **7-8** & **8-9** & **9-10** & **10-11** & **11-12** \\ \hline \(S_{2}\) (Air) & 45.53 & 50.46 & 54.08 & 54.47 & 55.13 & 55.20 & 55.11 & 55.07 & 55.06 & 55.06 & 55.05 \\ \hline \(S_{2}\) (He) & 47.84 & 49.92 & 53.28 & 56.06 & 57.66 & 57.15 & 55.34 & 54.31 & 53.71 & 53.32 & 53.10 \\ \hline \(S_{3}\) (Air) & 36.02 & 34.48 & 32.02 & 30.99 & 19.00 & 14.22 & 14.20 & 14.17 & 13.99 & 13.89 & 13.61 \\ \hline \(S_{3}\) (He) & 34.03 & 30.56 & 28.00 & 26.60 & 21.99 & 14.67 & 14.51 & 14.48 & 14.10 & 13.85 & 13.62 \\ \hline \(K\) (Air) & 47.40 & 56.20 & 64.90 & 130.50 & 138.50 & 219.60 & 447.60 & 1218.10 & 3596.30 & 10,828.20 & 33,126.60 \\ \hline \(K\) (He) & 1.31 & 1.89 & 2.36 & 3.41 & 4.32 & 6.16 & 9.50 & 14.51 & 22.24 & 34.00 & 52.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: \(S_{2}\), \(S_{3}\) and \(K\) at different inspection port positions. Figure 7: Relationship between the pressure \(p_{2}\) and fine inspection port.