# Analysis of Sealing Characteristics of Lip Seal Rings for Deep-Sea Separable Pressure Vessels
## 3 Results and Analysis
### Lip seal Sealing Performance  
The sealing performance of a seal depends primarily on the magnitude and distribution of the contact stress. When the contact stress exceeds the water pressure, the seal will not leak. Furthermore, when the effective contact width is greater than the width of the water pressure, the maximum contact stress will also exceed the water pressure. In other words, the greater the effective sealing pressure difference, the better the sealing  
Figure 8: Maximum equivalent force and maximum shear stress on lip seal at different water depths. Figure 9: Comparison of internal cavity deformation of lip seals at various water depths. performance [19]. Figure 10 illustrates the distribution of contact stress in the primary sealing area of the lip seal at various water pressures. As water pressure increases, the maximum contact stress of a lip seal in working conditions also increases continuously, and it always exceeds the water pressure. To analyze and assess the sealing performance of the seal, Table 2 presents the effective seal width and effective seal pressure difference of the lip seal at different water pressures. The effective seal pressure difference refers to the disparity between the maximum contact pressure and the prevailing water pressure, while the effective seal width represents the extent of the region where the contact pressure exceeds the current water pressure. At water depths ranging from 0 to 3 m, the contact area between the lip seal and the sealing surface of the upper spherical shell increases gradually from small to large. Consequently, the peak contact stress decreases gradually, and the effective sealing pressure difference also decreases progressively. As the water depth increases, the displacement of the upper spherical shell under pressure increases. Consequently, the lip seal is gradually flattened, and its effective sealing width increases gradually, compensating for the adverse effect of the decreasing sealing pressure difference. At water depths ranging from 3 to 10 m, the seal stabilizes as the effective seal pressure differential and the effective seal width gradually increase. Beyond a water depth of 10 m, the effective seal width gradually decreases while the effective seal pressure differential increases, resulting in a complementary state. This complementary state helps to maintain the seal state stably under low water pressure. When the water depth exceeds 100 m, the effective sealing width and pressure  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Water Depth** & **Effective Seal Width** & \\
**m** & **B/mm** & **Effective Seal Pressure Difference \(\Delta\)p/MPa** \\ \hline
0 & 2.6838 & 0.7761 \\
1 & 2.5573 & 0.6369 \\
2 & 5.2102 & 0.4501 \\
3 & 6.1423 & 0.3612 \\
6 & 8.8669 & 0.3575 \\
10 & 8.9864 & 0.6539 \\  
differential of the lip seal gradually decrease, leading to a weakening of the sealing effect under high-water pressure. To explain the extreme points of contact stress that appear behind the main sealing area of the lip seal in Figure 10 when the water depth exceeds 10 m, it is necessary to observe the contact stresses and deformations in detail. Figure 11 compares the contact stress distribution and nodal displacement vectors of the lip seal at different water depths. Figure 11a-c illustrates how the contact stress distribution changes with variations in water depth. Initially, the contact area between the lip seal and the shell surface is limited to the upper left end of the seal due to the supporting effect of the two seals. This leads to a smaller contact area and higher contact stress. As the water pressure acting on the upper spherical shell intensifies, the seal progressively compresses, leading to an expansion in the contact area and a concomitant reduction in the contact stress.