# Investigation of the Fluid Flow in a Large Ball Valve Designed for Natural Gas Pipelines
## 5 Conclusions  
The design of reliable and safe valves is crucial for the operation and extension of natural gas pipeline networks. In this work, fluid flow simulations for a DN 500 mm \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test–Fluid Test** & **Pressure (MPa)** & **Time (s)** & \
\begin{tabular}{c} **Fluid Flow Rate of Leakage** \\ **(ml/s)—Required Values** \\ \end{tabular} &
\begin{tabular}{c} **Fluid Flow Rate of Leakage** \\ **(ml/s)—Result Values** \\ \end{tabular} \\ \hline Hydrostatic shell test & 94.5 & 1800 & No external leakages & No external leakages \\ \hline Hydrostatic test of the upstream seat & 6.93 & 300 & 0.05 & 0.043 \\ \hline Hydrostatic test of the downstream seat & 6.93 & 300 & 0.05 & 0.041 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of hydrostatic tests performed with water as the working fluid. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test–Fluid Test** & **Pressure (MPa)** & **Time (s)** & \
\begin{tabular}{c} **Fluid flow Rate of Leakage** \\ **(Bubbles/s)—Required Values** \\ \end{tabular} &
\begin{tabular}{c} **Fluid Flow Rate of Leakage** \\ **(Bubbles/s)—Result Values** \\ \end{tabular} \\ \hline Hydrostatic test of the upstream seat—low-pressure air & 0.6 & 300 & 230 & 0 \\ \hline Hydrostatic test of the downstream seat—low-pressure air & 6.93 & 300 & 230 & 193 \\ \hline Hydrostatic test of the upstream seat—high-pressure air & 6.93 & 300 & 230 & 189 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of hydrostatic tests with air as the working fluid. trunion ball valve were performed for five positions of the ball--from slightly to fully closed--using SolidWorks Flow Simulation 2023. Based on the observation of the pressure fields, the velocity fields, and the trajectories, several conclusions can be put forward. For partially closed case studies, when the angle between the longitudinal axis of the pipe/ball valve and the longitudinal axis of the ball was 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), or 70\({}^{\circ}\), the increase in the closure angle modified the pressure fields and trajectories significantly. In large-diameter ball valves, vortices have enough space to develop; consequently, their amplitude is larger compared to small and medium-sized valves. Intense turbulence phenomena lead to high levels of unsteady stress on the sealing components and important pressure losses at high closure angles. The results obtained by simulation of a ball valve in intermediary closing positions strengthen the recommendation to construct ball valves merely for shut-on/off applications. This technical requirement is usually based on the difficulties of designing them in such a way as to be used as control valves, providing appropriate fluid flow characteristics. This paper demonstrates that in order to obtain reliability, the shut-on/off operation of large-diameter ball valves is mandatory. If the ball valve is supposed to operate for a long time interval in an intermediary opening position, the flow pattern should be studied by dynamic simulation to identify the risky areas. Thus, the internal geometry of the ball and of the sealing seats can be configured on a case-by-case basis by the mechanical engineer responsible for their design. The simulation for the case study with a closure angle of 90\({}^{\circ}\) demonstrates the importance of implementing the DPE seat type for good sealing of large-diameter ball valves. Some suppliers use an SPE design for upstream seats, because they are cheaper. Unfortunately, such sealing allows some particles to pass, and without DPE downstream seats, particles of fluid can be released in the pipe, which is unacceptable for natural gas as a fluid. Ball valves that work with water are exposed to the risk of cavitation and of erosion due to solid particles. Although ball valves working with natural gas are risk-free from this perspective, they are exposed to the risk of fire.