# Analysis of Sealing Characteristics of Lip Seal Rings for Deep-Sea Separable Pressure Vessels
## 3 Results and Analysis
### Lip Seal Strength  
The finite element calculations of the deformation and stress of the seal at different water depths are shown in Figures 7 and 8.  
Based on the data depicted in Figure 7a-h, it is apparent that the degree of vertical compression within the sealing ring exhibits a gradual increase as the depth of water increases from 0 to 14 m. This trend is attributed to the progressive convergence of the upper and lower lips, which move closer together. At a water depth of 14 m, the seal is fully compressed into the groove, and the internal cavity space between the upper and lower lips experiences the most severe compression. However, as the water depth continues to increase beyond 14 m, the degree of vertical compression within the seal no longer increases. Instead, the water pressure acting on the inner cavity space increases, causing it to gradually expand. This behavior is exemplified in Figure 7i-k. Based on the data presented in Figure 7, it is evident that the maximum equivalent stress and maximum shear stress occur in the bottom area of the inner lip cavity. This area represents a point of heightened susceptibility for the sealing ring with regard to potential failure mechanisms, such as tearing and fatigue.  
Figure 7: Stress distribution and deformation of the lip seal von Mises at different water depths.  
According to the data presented in Figure 8, it is evident that the maximum shear stress and maximum equivalent stress of the lip seal ring both increases in proportion to the water pressure up to the point at which the upper and lower sphere shells come into full contact with each other. After the upper and lower sphere shells are fully in contact, the data presented in Figure 8 shows that the maximum equivalent stress and maximum shear stress in the lip seal ring actually decrease as water pressure continues to increase.  
As depicted in Figure 9a,b, prior to the installation of the upper and lower spherical shells, an increase in water pressure resulted in noticeable vertical deformation of the lip seal. As a result, the upper and lower lips moved progressively closer together, leading to the most severe folding and squeezing of the material at the bottom of the inner cavity (i.e., the area marked by the black circle). Furthermore, the internal space was also subjected to compression. In contrast to Figures 8c and 9b, once the water depth exceeds 14 m and the upper and lower spherical shells are fitted together, the lip seal no longer exhibits increasing vertical deformation. As the depth of the water increases, the water pressure entering the inner cavity of the lip seal also increases. This increase in pressure props open the bottom of the inner cavity, thereby relieving the equivalent force and shear stress that would otherwise be present. When the lip seal of a separable sealed pressure vessel is fully fitted to the upper and lower spherical shell surfaces (i.e., the seal is fully pressed into the groove), the equivalent force and shear stress reach their maximum. As the water depth increases beyond this point, the stress decreases, which improves the sealing performance of the lip seal, reduces the risk of failure, and extends its service life.