What triggers the bi-directional XFLOW pump to deactivate?

The bi-directional XFLOW pump is designed to maintain fuel balance between the tanks on the aircraft. The activation and deactivation of this pump are based on specific weight thresholds between the two fuel tanks.

The correct trigger for deactivating the pump occurs when the low tank has 50 pounds more fuel than the opposite tank. This threshold is set to ensure that there is a sufficient fuel balance and to prevent over-pressurizing the tanks or causing unnecessary fuel transfer. When the low tank is at this specified level—50 pounds above the other—the system determines that it has effectively balanced the fuel load appropriately, thus deactivating the pump to conserve power and prevent unnecessary operation.

This specific weight difference ensures a stable, operational balance without risking the fuel systems under too much strain. The rationale for this threshold relates to maintaining efficiency and safety in fuel management within the aircraft systems. The other potential answers suggest values that either do not trigger the deactivation properly or do not align with the operational parameters of the system.