Originally Posted by johngreen
The low pressure pumps are something very much like this...
http://www.eatonaerospaceltd.com/fue...ump777_300.pdf
I beleive there are non return valves fitted in both the inlets and outlets and it is one or more of these that I am suggesting as being complicit in my post above.
There are two such pumps on either side of the aircraft and a smaller very similar one (on the left side I think) which is specifically for the APU.
JG
Thanks for the link!
These are the boost pumps, sucking directly from the tanks, located in the wings, and supplying positive pressure to the fuel manifolds.
There are in fact 7 such pumps, two in each wing tank, supplying their respective manifolds, and two in the centre tank, each supplying one manifold. There is an additional, DC-powered, pump in the left wing tank, feeding the left manifold, that can be used to start the APU if both main generators are offline.
I do not know if it can create enough flow to supply one or both main engines.
When one refers simply to "low-pressure pump", one usually means the engine's LP pump, which is part of the engine, and directly driven by the engine, and not the (electrically driven) boost pump.
As far as I know, the engine LP pump is also of centrifugal/impeller type, but whether or not it does have a dedicated check (no-return) valve I do not know.
Bernd