B 737-500 DC booster pump
 

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.

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).

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 :)