Which valve opens during the idle mode to allow defueling in the type 3 system?

The correct choice identifies the valve that operates in the idle mode specifically to facilitate defueling within a type 3 system. In many fuel system designs, certain valves have designated roles based on operational modes, including idle or defueling states.

The 58AF-9-1 valve is specifically designed to open during idle mode, allowing for the safe and controlled defueling of the system. This function is crucial for maintaining operational efficiency and safety, particularly when the system needs to be drained or adjusted without causing pressure buildup or contamination issues.

Other valves mentioned may serve different functions or operate under different conditions within the system, not specifically designated for idle mode defueling, which is why they are not the correct answer. Understanding the specific application and operational role of each valve in context is key to successfully navigating water and fuel systems maintenance protocols.