Which valves are used to control the flow of gases and liquids during gas fitting?

The selection of ball valves as the correct answer is based on their specific functionality and advantages in controlling the flow of gases and liquids. Ball valves are highly effective for this purpose because they provide a straightforward on/off control with minimal resistance to flow. This design incorporates a spherical closure element that rotates within the body of the valve. When the valve is fully open, the ball aligns with the flow direction, allowing for a smooth passage of the medium, resulting in very little pressure drop.

Additionally, ball valves are favored for their durability and reliability, making them suitable for various applications where tight seals and long service life are crucial. They are often used in high-pressure situations and with both gas and liquid mediums, as they effectively prevent leaks when closed.

In contrast, other valve types have different primary functions. For instance, gate valves are typically used in applications where a straight-line flow of fluid with minimal restriction is necessary; however, they do not provide precise flow control. Check valves are designed to prevent backflow, meaning they allow fluid to flow in one direction only, rather than regulating flow. Globe valves are more commonly used for throttling purposes and controlling flow rates, but they can create more resistance and are not as efficient as ball valves for quick shut-off applications