T&T: Fuel piping arrangements

[Ken Bloomfield]

I would caution against taking a pipe from the outside bottom of a tank for 
fuel for the following reasons:

1.  I believe it is against ABYC (and I suspect UK authorities) design 
requirements, for very good reasons.
2.  If you get a leak/crack/puncture, you will have a steady stream into the 
bilge, creating a diesel fuel swimming pool and all that brings with it.

When the fuel is taken from the top of the tank with a standpipe, the lift 
pump will have no more suction requirement than if it was from the bottom, 
assuming there is no leak in the line.  This may be understood with the 
concept of the siphon (aka syphon).  The only suction that the lift pump 
would need to create would be the difference between the level of the fuel 
in the tank and the level of the lift pump.  This is the case regardless of 
which tank takeoff method is used.

If you take the fuel from the top of the tank, then:

1.  You will be utilizing good design procedure, and
2.  If there is a leak/crack/puncture, only a little fuel will dribble into 
the bilge, and most of the line will run back into the tank.

In either case, it is important to not have leaks in the line to the engine, 
due to the well-known dislike that diesels have for air.

Cheers,
Ken.