## 3 Results and Discussion
Results showed that with the application of a six-bar mechanism to the valve, there was no significant difference in the flow efficiency of the valve. The flow coefficient for the original design was taken from the manufacturer's catalogue for DN 25 globe valve. The flow coefficient obtained from the simulation was higher when compared to the original due to the frictionless assumption in the analysis whereas values from the experiment were lower than rated. This is because the surface finish of the prototype from the plastic 3D printing was lesser quality when compared to the metal finish. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Input Displacement (mm)**} & \multicolumn{2}{c}{**Output Displacement (mm)**} \\ \cline{2-3}  & **Simulation** & **Experiment** \\ \hline
2.0 & 5.0 & 4.9 \\
4.0 & 10.0 & 9.9 \\
6.0 & 15.0 & 14.6 \\
8.0 & 20.0 & 19.5 \\
10.0 & 25.0 & 24.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of output displacement from simulation and experiment. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Valve Opening (\%)**} & \multicolumn{2}{c}{**Bellow Displacement (mm)**} \\ \cline{2-3}  & **New Design** & **Original Design** \\ \hline
75 & 2.5 & 6.25 \\
50 & 5.0 & 12.50 \\
25 & 7.5 & 18.75 \\
0 & 10.0 & 25.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Bellow displacement comparison of the original and new design. Figure 10: Flow coefficient comparison with original design. Figure 9: Valve actuation force comparison at: (**a**) 10 kPa; (**b**) 20 kPa; (**c**) 30 kPa; (**d**) 40 kPa; (**e**) 50 kPa. As described in the Introduction, the problem of long bellow lengths exists in bellow valves to produce the required disc motion. Our goal was to minimize the length of the bellow required by using the mechanism synthesized to generate the same output motion at the disc. In this research, a DN 25 bellow globe valve was used. The bellow length in the valve was about 305 mm, which makes the height of the valve significantly long. To fully open and close the valve, the disc has to cover the displacement of 25 mm. Using the linkage synthesized above, a mechanism was designed for the valve that reduced the input displacement required by keeping the output constant. Reduced input will in turn reduce the length of the bellow required for the valve. For this purpose, CAD software was used to model the mechanism for opening and closing the valve. The output link of the mechanism was attached to the disc and input link was attached to the bellow. By rotating the handle wheel, the rotary motion of the hand wheel was converted into the translatory motion of a rod by screw threads. The other end of this rod was attached to the mechanism and acted as the input link. The translatory motion produced in this rod was converted into a larger displacement at the disc through the mechanism. A bellow was attached to the valve with one end connected to the rod while the other was connected to the valve bonnet to provide sealing. The attached bellow compressed with the translatory motion of the valve while closing the valve and came back to its natural position while opening. Due to the small displacement of the input rod, the length of the bellow was significantly reduced or in this case, the length of the bellow was reduced to 50 mm if the material of the bellow was 316 L stainless steel as the displacement required to produce the desired output was only 10 mm. Bellow valves are a potential solution for no emissions from the valve, but their long length restricts their use until necessary. In the sections above, a mechanism was synthesized and analyzed to solve the problem of the long height of the bellow valve. From the literature, the height of the bellow valve was defined by the length of the bellow. By introducing the synthesized linkage to the bellow valve, less input displacement could be converted into the required output motion. This reduced the requirement of the long bellow length, which as a result, reduced the height of the valve.