## 3 Test Plan and Process  
### Test Plan  
The operating parameters of the mechanical seal are shown in Table 3. The mechanical seal is operated under low-rotational-speed and low-pressure conditions, and an effective  
Figure 2: Morphologies of triangle (**a**), ellipse (**b**) and conventional spiral groove (**c**) texture patterns. hydrodynamic pressure cannot be formed by the rotary and stationary rings [23; 24]. As a result, the friction pairs (rotating and static rings) are kept in contact. The test was divided into three stages. The first stage was for the friction pairs mated with different materials, the second stage was for the friction pairs with the single surface texture patterns, and the third stage was for friction pairs in the bi-composite surface texture configurations. The rotational speed and load were the inputs of the surface friction and wear testing apparatus used in this test. According to the actual operating and structural parameters of the mechanical seal (shown in Table 3) and the size of the specimen in this test (shown in Figure 1), the linear velocity and pressure of the actual sealing rings must be consistent with that of the seal specimens because of the difference in size between the actual sealing rings and the seal specimens. According to the data in Table 3 (medium pressure was 0.3 MPa and rotating speed was 15-35 rpm) and Figure 1 (the contact area with an inner diameter of 20 mm and an outer diameter of 34 mm), the load was determined to be 200 N (contact area and medium pressure) and the working conditions of the seal specimens were 100-300 rpm, in which 250 rpm was the cruising speed. In addition, the first stage of the test involved 100, 150, 200, 250, and 300 rpm. The surface friction and wear testing apparatus increased speed from 0 to 100 rpm, and increased by 50 rpm at regular intervals, before finally reaching 300 rpm. The above process takes 6 min. At the same time, considering the fluctuation of the speed in the surface friction and wear testing apparatus and the integrity of experimental data, the operating time was set to 480 s. The detailed description of the test groups and the test plan are shown in Table 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{Group 1 Friction Pairs of Different Materials} \\ \hline No & Friction Materials & Load \(F\) (N) & Speed \(n_{\text{r}}\) (rpm) & Time \(t\) (s) \\
1-A1 & M120D–SSiC & 200 & 100–300 & 480 \\
1-A2 & SSiC–SSiC & 200 & 100–300 & 480 \\ \hline \multicolumn{5}{c}{Group 2 Friction pairs of single surface texture patterns} \\ \hline No & Texture & Load \(F\) (N) & Speed \(n_{\text{r}}\) (rpm) & Time \(t\) (s) \\
2-B1 & Triangle & 200 & 250 & 480 \\
2-B2 & Ellipse & 200 & 250 & 480 \\
2-B3 & Conventional spiral groove & 200 & 250 & 480 \\ \hline \multicolumn{5}{c}{Group 3 Friction pairs of bi-composite surface texture configurations} \\ \hline No & Texture & Load \(F\) (N) & Speed \(n_{\text{r}}\) (rpm) & Time \(t\) (s) \\
3-C1 & / & 200 & 250 & 480 \\
3-C2 & Triangle–Ellipse & 200 & 250 & 480 \\
3-C3 & Triangle–Conventional spiral & 200 & 250 & 480 \\  & groove & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Test grouping scheme. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Operation Parameters** & **Symbol** & **Value** \\ \hline Rotating speed & \(n_{\text{r}}\) & 15–35 rpm \\ Cruising speed & \(n_{\text{r}}\) & 32 rpm \\ Pressure of water intake & \(p_{\text{in}}\) & 0.8–1 MPa \\ Pressure of backwater & \(p_{\text{out}}\) & 0.2–0.4 MPa \\ Flow & \(Q\) & 66 m\({}^{3}\)/h \\ Medium pressure & \(p\) & 0.3 MPa \\ Outer diameter of the seal face & \(d_{\text{o}}\) & 210 mm \\ Inner diameter of the seal face & \(d_{\text{i}}\) & 198 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Operating parameters of mechanical seal. Friction pairs with different materials  
The 1-A1 group (M120D-SSiC) and the 1-A2 group (SSiC-SSiC) were tested with a constant load of 200 N and rotational speeds in the range of 100-300 rpm at an interval of 50 rpm.