Fellow Spitsters,
Not to be too contrary, but even though the initial loading (priming)
of the fuel pump will be with suction, after the pipe is full from the
bottom of the tank to the pump, there will no longer be any gravity
for the pump to overcome -- the rising fuel is exactly balanced by the
falling fuel, and as long as the pump is lower than the in-tank
opening of the pick-up, this [siphon] action will reduce the lift
requirement of the pump. Now the other side of this story is that the
level of the outlet of the pump also affects the pressure differential
that the pump operates against, and since the pickup point and the
delivery are at a constant differential height, (depending on road
grade, though) the pump operates against a constant head. So it
doesn't really matter to the pump, (who probably doesn't even see this
simple situation -- remember the carb float valve is closed most of
the time, so the output is deadheaded. And as long as the pump is in
the trunk, the fuel should be cool enough to stay away from vapour
lock, so the fact that there may be suction on the supply side of the
pump is nearly irrelevent. But wait! there's more!
(Sorry to be so long-winded.) For safety, if you power the fuel pump
through a relay controlled by lube pressure, you should be safer in
case of serious shunt. And this would not significantly alter
starting characteristics -- either there is sufficient fuel in the
carb bowls to start, (in which case oil pressure rises quickly, pump
begins delivering fuel, and all is ducky) or the cranking raises the
oil pressure (albeit with a bit of delay) and the pump begins
delivering, the bowls fill, engine starts, and THEY'RE OFF!
Donald.
(who saved up three weeks of postings just for this occasion!)
> Date: Tue, 07 Mar 2000 09:01:34 -0700
> From: Joe Curry <spitlist@gte.net>
>
> "Terry L. Thompson" wrote:
> >
> > I've been debating where to mount my electric fuel pump,
> > and one of the suggestions is that the pump should be below
> > the fuel tank (when the car is level) so that the pump is
> > gravity fed, and has less work to do.
>
> That is not so with the later Spitfire tanks. The reason is because
> regardless of where the pump is located, the fuel is sucked out of the
> tank from above via a suction tube that is located on top to the right
> of the fuel inlet. On earlier bottom feed tanks it does apply.
> >
> > The two places I've considered are A) in the trunk near
> > the gas tank which is some distance from the carb or B)on
> > the frame perhaps next to the starter, which puts it very
> > close to road debris from the tires.
> >
>
> Because of safety concerns, I located mine in the trunk. Shoiuld one of
> the rubber hoses rupture the fuel would be kept in the trunk area rather
> in the engine compartment next to heat and sparks (starter commutator).
>
> > If anyone has a decent mounting point, away from a hot spot
> > and interference of moving parts, I'd like to know, so I
> > only have to re-run the fuel line once.
> >
> Mine is to the left and below the tank in the void between the tank and
> the floor of the trunk.
>
> Regards,
> Joe
>
>
> --
> "If you can't excel with talent, triumph with effort."
> -- Dave Weinbaum in National Enquirer
>
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