# Design of Quadruple Offset Butterfly Valve Used in Power Plants
## 3 Finite Element Analysis
### Design of Laminated Seal Thickness of Seven-Layers Model  
To increase the performance of the seven-layers laminated seal, the thickness design of stainless steel and graphite was conducted. With the same arrangement of the seven-layer model suggested above (SS/G/SS/G/SS/G/SS), the thickness of stainless steel varies from 0.7 mm\(\sim\)1.6 mm at an interval of 0.3 mm. Since the total thickness of the seal was fixed at 7 mm, the thickness of graphite varies from 1.4 mm\(\sim\)0.2 mm at the interval of 0.4 mm, and four analysis models were generated, as shown in Figure 20. Designs 1-4 were indicated to the thickness of 0.7 mm (SS) and 1.4 mm (G), 1 mm (SS) and 1 mm (G), 1.3 mm (SS) and 0.6 mm (G), and 1.6 mm (SS) and 0.2 mm, respectively.  
The thermal-structural coupled analyses were implemented, and the results are listed in Table 5. By increasing the SS thickness and reducing the graphite, the contact pressure from the SS surface was reduced, and the G was increased. The results of the description were the following:  
Design 1 produced the maximum contact pressure of 98.9 MPa (SS) and 0.87 MPa (G). Compared with working pressure, the stainless steel (SS) prevents leakage, but the contact pressure of the graphite (G) was less than the work pressure (1 MPa), which leads to leakage problems.  
Design 2 produced the maximum contact pressure of 94.69 MPa (SS) and 1.4 MPa (G), and it exceeds the work pressure and provided good performance in the simulation section,  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **TOBV** & **QOBV** \\ \hline A & 18.960 MPa & 22.169 MPa \\ B & 22.622 MPa & 23.241 MPa \\ C & 46.122 MPa & 25.343 MPa \\ D & 29.906 MPa & 16.278 MPa \\ E & 28.429 MPa & 29.498 MPa \\ F & 13.190 MPa & 11.627 MPa \\ G & 148.90 MPa(max) & 93.469 MPa (max) \\ H & 13.548 MPa (min) & 9.6218 MPa (min) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of the contact pressure of TOBV with that of QOBV.  
Figure 19: The contact pressure distributions of TOBV and QOBV.  
but the value (1.4 MPa) of existent contact pressure was close to work pressure (1 MPa). This leads to a dangerous actual sealing state, which may lead to leakage problems in the experimentation.  
Design 3 produced the maximum contact pressure of 86.8 MPa (SS) and 3.68 MPa (G), shown in Figure 21. Both seal parts of the stainless steel (SS) and the graphite (G) not only produced a good sealing, but also produced a safe contact pressure value graphite (G) compared with design 2.  
Design 4 produced the maximum contact pressure of 76.15 MPa (SS) and 8.55 MPa (G), although the contact pressures of the stainless steel (SS) and the graphite (G) exceeded the working pressure (1 MPa) shown in Figure 22. The most common form of compressed expanded graphite (CEG) thickness is from 0.3 to 5 mm [23], so the graphite thickness of 0.2 mm would lead to a high cost in manufacturing.  
For these reasons, design 3 was suggested as the best design, whose contact pressures were not only sealed satisfyingly, but it is also less costly than design 4 (G: 0.2 mm) in its manufacturing.