Which valve type typically has the least flow resistance when fully open?

The ball valve is known for having the least flow resistance when fully open due to its design. In a ball valve, the flow path is unobstructed as the spherical ball containing a hole or port is rotated to align with the pipeline. This creates a straight-through flow path, which allows fluid to pass with minimal friction and turbulence.

Additionally, ball valves open and close rapidly, providing a quick on-off function, and when they are fully open, they practically do not impede the flow. This is in contrast to globe valves and gate valves, which, while effective for controlling flow, introduce more resistance due to their internal geometry and the way they manage fluid flow. Globe valves have a more complex passage that leads to higher resistance, and gate valves, while providing good flow characteristics when fully open, do not achieve the same level of minimal resistance as ball valves do. Check valves, on the other hand, are designed primarily to prevent backflow rather than to facilitate maximum flow, thus also limiting performance when it comes to flow resistance.

Consequently, the ball valve stands out as the optimal choice for applications requiring low flow resistance when in the fully open position.