## 3 Results and Discussion
### Relationship between the Position of the Fine Inspection Port and Detection Characteristics
Figure 10: Relationship between the return flow ratio and fine inspection port. the higher the detection sensitivity. This result occurred because as the opening position moved downwards, the number of turbine blades between the mass spectrometer chamber and the opening increased, the compression ratio increased, and the return flow decreased. Therefore, larger leakage holes were required to meet the detected helium return flow. In addition, this result was the reason the countercurrent leak detection method was not as direct and rapid as the downstream leak detection method [26]. Moreover, \(Q_{2}\) represented the air return flow, and this parameter first decreased rapidly and then tended to be stable as the opening position moved downwards. The leakage rate \(Q_{1}\)\({}^{\prime}\) of helium molecules from leakage holes at different positions of the fine inspection port was calculated by the fine inspection port model. As shown in Table 5, the return flow \(Q_{2}\)\({}^{\prime}\) of helium entering the mass spectrometer chamber was the minimum detectable leakage rate. When the fine inspection port was located between the 7 th- and 8 th-stage blade rows, the detectable air leakage rate \(Q_{1}\) reached 6.48 \(\times\) 10\({}^{-12}\) Pa-m\({}^{3}\)/s, and the air return flow \(Q_{2}\) was 6.36 \(\times\) 10\({}^{-14}\) Pa-m\({}^{3}\)/s. Ninety-nine percent of the air was pumped out, and the proportion of the helium reflux was 28.57%. The return flow of helium was much greater than that of air, so a higher detection sensitivity was obtained. 2.4 Overall Performance of a Helium Mass Spectrometer Leak Detector Using a Multiport Hybrid Molecular Pump  
Comprehensively considering the actual use requirements of the leak detector, such as the working pressure of the inspected part, the leak rate and the minimum detectable leak rate, it was determined the optimal position of the fine inspection port of the multiport hybrid molecular pump prototype was between the 7 th- and 8 th-stage blade rows. Figure 12 shows a photograph and schematic diagram of the prototype. The multiport hybrid molecular pump prototype was applied to the helium mass spectrometer leak detector for the overall performance test. The maximum leak detection pressure could reach 1000 Pa, and the minimum detectable rate was 2.42 \(\times\) 10\({}^{-12}\) Pa-m\({}^{3}\)/s, which indicated that after the application of a multiport hybrid molecular pump, the helium mass spectrometer leak detector combined the high detection accuracy of downstream  
Figure 7:0 Multiport hybrid molecular pump: (**a**) prototype photograph, (**b**) schematic of the structure. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Position** & **b-2** & **b-3** & **b-4** & **d-8** & **e-4** & **f-7** & **b-6** & **e-9** & **b-10** & **b-11** & **b-12** \\ \hline \(Q_{1}\)(\({}^{\prime}\)/s,m\({}^{\prime}\))/s & 9.66 \(\times\) 10\({}^{-12}\) & 1.08 \(\times\) 10\({}^{-11}\) & 11.2 \(\times\) 10\({}^{-11}\) & 1.31 \(\times\) 10\({}^{-11}\) & 1.32 \(\times\) 10\({}^{-11}\) & 1.29 \(\times\) 10\({}^{-11}\) & 1.25 \(\times\) 10\({}^{-11}\) & 2.43 \(\times\) 10\({}^{-11}\) & 3.02 \(\times\) 10\({}^{-11}\) & 49.8 \(\times\) 10\({}^{-11}\) & 7.18 \(\times\) 10\({}^{-11}\) \\ \hline \(Q_{2}\)(\({}^{\prime}\)/s,m\({}^{\prime}\))/s & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) & 5 \(\times\) 10\({}^{-12}\) \\ \hline \end{tabular}
\end{table} 
Table 5: \(Q_{1}\)\({}^{\prime}\) and \(Q_{2}\)\({}^{\prime}\) at different fine inspection port positions. detection and the high leak detection pressure of countercurrent detection to widen the detection range of the helium mass spectrometer leak detector. At this stage, there is only one prototype of the multiport hybrid molecular pump that has been completed.