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Guest s_L_Y_F_a

What is this?!

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Guest s_L_Y_F_a

All pumps off but engines running at full power...This isn´t realistic or is it :-eek ?

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Guest Matthias1975

Sorry Paul,this is realistic :-)In case of fuel pump pressure is lost, each engine is able to suction fuel from it

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Guest s_L_Y_F_a

thx 4 the info quite amazing that it even works will full thrustbut are those pumps the same as the ones you can turn on /off on your overhead or are they seperate ones that cant be controlled by the flightcrew?

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Guest D17S

The engines have engine driven fuel boost pumps too. As the description indicates, these pumps are bolted directly to the engine. Any time the engine is turning; these pumps turn too . . . and make pressure. You have no control here. The purpose of these pumps is to increase the fuel's pressure before it

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Guest neeraj.pendse

Great explanation, Sam! Loved it. One question: in normal condition, all tanks are connected to all engines, right? So is this connection thtough the Tank Boost Pumps? And when they are OFF, the engine driven pump (+ gravity, I suppose) will allow head pressure to develop because other pumps are off and blocked? Obviously this will allow only 1 tank to be connected to the engine.- Neeraj

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Guest D17S

Excellent. We

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Guest s_L_Y_F_a

wow I didnt want it that exactly but thx anywaynow I know much more about the fuel system.Much appreciated

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Sam et al,My take on how to get the fuel pass the pumps.It's probably a rotodynamic pump, and if so there is really nothing to prevent the fuel to flow around the impeller. Think of a bow propeller on a big ship. If the propeller wasn't used, would the water flow around the blades or not?Only if the pump was of a displacement type would be have to have a bypass of some sort. But having a displacement pump on a modern jet does not make any sense.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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I've been told that some fuel will leak through the pumps (to be confirmed), but there are completely separate pick up points/plumbing for gravity/suction feed which bypass the tank pumps completely. Check valves keep the bypass system closed when the tank pumps are operating.Note that you don't want a vacuum being created in the tanks when the fuel is being sucked out of them. A small positive pressure is maintained in the tanks by the naca scoops underneath each wing and the vent system.Hope this helps.Cheers.Q>

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