The symbol shown below designates the valve is _______ operated.

The symbol designating that the valve is float operated indicates a specific type of control mechanism where the operation of the valve is directly influenced by buoyancy. In float-operated valves, a float mechanism rises or falls according to the level of liquid in a tank or another system. When the liquid level rises to a certain point, the float triggers the valve to close or open, thus controlling the flow of the fluid based on the predetermined level.

This method of operation is commonly used in applications where maintaining a specific liquid level is critical, such as in water tanks or sump pumps. The float provides a simple yet effective means of automation without requiring complex electrical or mechanical systems.

In contrast, the other options describe different operation methods. Manually operated valves require direct human action to open or close, electronically operated valves utilize electrical signals for control, and mechanically operated valves are usually influenced by a physical mechanism, such as a handle or lever. Each of these methods has its unique applications and advantages, but the specific context of the question clearly points to float operation as the method being described.