What method would be used to check for internal leakage of a fuel valve without removing the valve from the aircraft?

The method described is effective for checking internal leakage of a fuel valve while it remains installed in the aircraft. By placing the valve in the OFF position and draining the strainer bowl, one can effectively isolate the valve from the rest of the fuel system. If there is any internal leakage present, turning on the boost pump will create pressure within the system. Observing fuel flowing back into the strainer bowl indicates that the valve is not fully sealing and is allowing fuel to pass through despite being in the OFF position.

This method is advantageous because it does not require removal of the valve, thus saving time and effort in troubleshooting. It's a practical approach in maintenance checks, allowing technicians to assess valve integrity with minimal disruption to the aircraft's fuel system.

In contrast, other methods such as applying air pressure or monitoring fuel levels in tanks would not provide a reliable assessment of internal leakage specific to the valve in question, as they test different aspects of the fuel system or do not isolate the valve's condition effectively.