Which type of valve is best suited for controlling the water level in a treated water storage reservoir located below the hydraulic gradient?

The altitude valve is specifically designed for controlling the water level in a reservoir by responding to changes in water level. When installed in a treated water storage reservoir, it opens or closes based on the elevation of the water level, thus regulating the flow into or out of the reservoir. This feature is particularly useful in applications where water needs to be maintained at a specific level, especially when the reservoir is situated below the hydraulic gradient, which can affect the pressure and flow dynamics.

The altitude valve operates automatically, allowing for more consistent control over the water level without manual intervention or complex control systems. Its design typically includes a float mechanism that directly influences the valve position, providing precise responses to fluctuating water levels.

In contrast, other valves like globe and ball valves are not specifically designed for level control. While they can regulate flow, they lack the automatic adjustment feature that altitude valves provide. Additionally, check valves are meant to prevent backflow and do not regulate level or flow in the way required for maintaining water levels in a reservoir. Thus, the altitude valve is the most suitable choice for this application, given its functionality and purpose.