## 3 Results and Discussion
### Influence of the Turbine Blade Structure Parameters on the Inspection Performance  
Single-stage dynamic blade parameters were selected to study the influence of turbine blade structure parameters on the inspection performance. The speed of the turbine blade was 72,000 r/min. The blade length \(l\), blade height \(h\), blade number \(z\), blade inclination \(\alpha\), and blade thickness t are shown in Table 3.  
The compression ratio \(K_{1}\) of the turbine blades to air and \(K_{2}\) of helium for different blade inclinations \(\alpha\), numbers of blades \(z\), and blade heights \(h\) were calculated. In addition, \(K_{1}/K_{2}\) was used to measure the variation in the helium mass spectrometer leak detector inspection sensitivity with respect to the blade parameters. A larger \(K_{1}/K_{2}\) means that more air is extracted. Thus, if the partial pressure of helium in the mass spectrometer chamber is higher, then the leak detector is more sensitive. Additionally, the variation in the maximum air pumping speed \(S\) was compared, and the parameter value of the turbine blade, which took into account the pumping performance and detection sensitivity, was discussed. The calculation results are shown in Figure 6.  
From Figure 6a, as the blade inclination angle increased, \(K_{1}/K_{2}\) gradually decreased, and \(S\) increased. The decrease in \(K_{1}/K_{2}\) indicated that the compression ratio of air decreased faster, which would cause a relative increase in air reflux and a decrease in the partial pressure of helium in the mass spectrometer chamber. Moreover, the detection sensitivity of the leak detector was reduced. Taking into account the pumping speed of the molecular pump, a blade inclination of 25\({}^{\circ}\) was selected, the pumping speed \(S\) was set to 57 L/s and \(K_{1}/K_{2}\) was 1.65. These parameters provided highly sensitive leakage detection while ensuring pumping performance.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \(l\)/mm & \(h\)/mm & \(z\) & \(\alpha\)/(\({}^{\circ}\)) & \(t\)/mm \\ \hline
7.5 & 2 & 24 & 30 & 0.8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Turbine grade single blade parameters.  
As shown in Figure 6b, \(K_{1}/K_{2}\) gradually increased and \(S\) decreased as the number of blades increased. The increase in \(K_{1}/K_{2}\) indicated that the compression ratio of air rose faster, which reduced the backflow of air, increased the partial pressure of helium in the mass spectrometer chamber, and increased the detection sensitivity of the leak detector. When the number of turbine blades was between 25 and 30, \(K_{1}/K_{2}\) was between 1.52 and 1.64, and the pumping speed \(S\) increased to more than 50 L/s, the turbine blade row provided ideal pumping performance, and the helium mass spectrometer leak detector was highly sensitive.  
As shown in Figure 6c, with an increasing blade height, \(K_{1}/K_{2}\) gradually increased, and \(S\) decreased. This result showed that increasing the height of the blade increased the detection sensitivity of the leak detector. When the blade height was 3 mm, the \(K_{1}/K_{2}\) value was 1.69, and the pumping speed \(S\) was greater than 55 L/s. The pumping performance was good, and the detection sensitivity of the leak detector was high.