The least amount of head loss in a pipeline would be the result of a fully open which type of valve?

A fully open gate valve is designed to provide minimal resistance to flow when it is fully opened, allowing water to pass through with little to no obstruction. This feature significantly reduces head loss compared to other types of valves. The design of a gate valve involves two flat surfaces that meet when the valve is closed, but when it is opened fully, the gate is lifted out of the way entirely, creating a clear pathway for the fluid.

In contrast, valves such as globe valves and butterfly valves can create more turbulence and resistance even when fully opened. Globe valves, specifically, are designed for throttling flow rather than allowing a full flow opening, which increases head loss. Butterfly valves, while they can be efficient, still have a disc that may partially obstruct flow even when opened, leading to a higher potential for head loss than a fully opened gate valve.

Check valves are designed to prevent backflow and are not used primarily for flow control. When fully opened, they may still have some inherent resistance due to their internal mechanism. Therefore, the least head loss in a pipeline occurs with a fully open gate valve, which allows for the most unobstructed flow.