What mechanism stops fuel from filling in an aircraft fuel system?

The check valve is a crucial component in an aircraft fuel system that ensures fuel flows in the correct direction and prevents backflow. This mechanism is designed to stop fuel from leaking back into the tank once it has been pumped into the system. It operates by allowing fuel to pass through it only when there is sufficient pressure from the fuel pump, and it closes when that pressure drops or the flow reverses. Thus, it helps maintain the integrity and efficiency of the fuel supply by preventing overfilling and ensuring that the fuel remains where it is needed within the system.

In contrast, the fuel gauge sensor primarily monitors the fuel levels within the tanks but does not actively prevent fuel from filling. The overflow valve is designed to release excess fuel when a tank is overfilled, yet it does not stop fuel from filling initially. The fuel pump switch controls the operation of the fuel pump but does not have a mechanism specifically designed to stop fuel from filling in the system. Each of these other components serves vital functions, but they do not address the backflow prevention and filling stop role that the check valve provides.