Which type of valve has the lowest friction loss when fully open?

The gate valve is recognized for having the lowest friction loss when fully open due to its design. When a gate valve is fully opened, the gate is completely withdrawn from the flow path, allowing for a straight, unobstructed passage for water. This design minimizes turbulence and resistance, which are key contributors to friction loss in a system.

In contrast, other types of valves do not allow for such a clear flow path. For instance, while a ball valve also provides a largely unobstructed flow when fully open, its design can introduce some turbulence around the ball, leading to slightly higher friction loss than a fully opened gate valve. Globe valves are designed for throttling and control and have a geometry that causes significant turbulence even when fully open, resulting in higher friction loss. Check valves, which are used to prevent backflow, also create restrictions in the flow path, leading to increased friction loss compared to a gate valve.

By understanding these flow characteristics, it becomes clear why the gate valve is the most efficient option among the choices when fully open, making it preferable in applications where minimal friction loss is crucial.