B 737-500 DC booster pump

[giopi]

Can anyboby tell me something more about a DC booster pump in the left main tank of the B737-500? Is it installed on all the 500s?
I couldn`t find anything about that anywhere. Just in the Derek Watts` fuel schematic.

Thank you.

[Gary Lager]

It's to supply APU fuel pressure when main pumps are off. Maybe not all 500s have it, but (most of) ours do (I think).

[vapilot2004]

The DC pump assists in fuel pressure boost for APU startup when no AC power is available for the L main tank pumps - a consideration for the -500 which can operate out of smaller (and more bucolic) airports where power carts/ground AC theoritically wouldn't always be available.

The -500 is usually equipped with a dedicated APU battery using the same reasoning - self-reliance on the ground.

I wouldn't be surprised if a few airline-spec'd -500's did not have the DC pump - but don't have any direct knowledge regarding the omission.

EDIT: Oh hello Gary - simultaneous post nearly - you beat me to it :)