787 Fuel Tank Pressure & NGS System
Hi folks, I'm trying to understand the fuel tank venting/pressurisation system on the 787-8. I did see a diagram of this system, but it had check valves in unexpected places. On more traditional aircraft, tanks are pressurised by the NACA scoops under the wings, but I don't see any of these in 787 photos.... just what looks like overpressure valves.
Do the fuel tanks rely solely on pressure from the NGS system, and if the pressure is generated electrically, would a dual engine failure (as some theorised in the Air India incident) stop the generation system operating? If so, how are vacuums prevented in the tanks. Can air get into the tank through the surge tank drains or other places?
Also, MEL 29-11-03-02 for the Centre Hydraulic System Left Pump Auto function inops the NGS system. I know the NGS and Centre Hydraulic Pumps are driven by the "Large Motor Power System", but why should AUTO hydraulic pump operation affect the NGS?
Thank you.