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Old 24th Nov 2009, 22:29
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flybik
 
Join Date: Oct 2009
Location: slovenia
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boeing 747 fuel system

Short from PMDG maual:

Any engine can draw fuel from any fuel tank, fuel can only be suction fed from the main wings tanks.
Each main tank and stab tank has AC boost pump + inboard main tanks and center wing tank have override/jettison AC pump.
Center tank has a scavenge pump that will automaticly transfer fuel to main tank 2 if center tank fuel pumps detect low pressure.
A vented surge tank is located near the tip of each wing and provide positive pressure on fuel tanks during cruise.
Each reserve tank has two automatic transfer valves that alow gravity transfering of fuel to inboard tank when inboard tank fuel quantity decreases below 40,000 lbs.
Outboard main tanks have each one manual transfer valve that allow fuel (7,000 lbs remain in each outboard tank) to be gravity transfered to inboard tank. Valves open automaticaly durring jettison if inboard tank fuel quantity decreases below 20,000 lbs.
When center wing fuel tank quantity decreases below 80,000 lbs fuel will be transfered from stab tank.
APU drives fuel from main tank 2 that also has DC boost pump.

Questions:
1. Does each engine has accessory drive attached fuel suction pump?
2. If so from where does this pump suction fuel from - where is the pump's inlet connected? Can engine one suction fuel from any tank?
3. Does stab tank really has boost pump, since the symbol for pump (on secondary EICAS under FUEL) is the same as for overide/jettison pumps and fuel is also fed from this tank in fuel jettison operation?
4. Where does stab tank fuel outlet goes (they are only pictured when fuel jettison is armer)? Can stab tank pumps provide fuel to the crossfeed manifold as other boost pumps?
5. What is a vented surge tank?
6. Can fuel from reserve and outboard tanks only be gravity transfered to inboard tanks?
7. What is the scavenge pump flow and is it AC or DC powered?

Last edited by flybik; 24th Nov 2009 at 22:41.
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