Fuel pump questions

[Shannen Durphey]

James Tidwell wrote:

> At 01:03 PM 12/10/97 -0800, you wrote:
> >Fuel splash tends to generate large amounts of vapor that must
> >go through the purge canister to eventually exit to the engine.  In
> >theory this should all be accounted for by the EFI system.  In practice,
> >you can find driveability problems associated with large amounts of
> >purge vapors.
> >
> >Jim Boughton
> >jpb01 at ibm.net
> >
> >----------
> >> From: Bruce Bowling <bowling at cebaf.gov>
> >> To: diy_efi at efi332.eng.ohio-state.edu
> >> Subject: Re: Re[2]: Fuel pump questions
> >> Date: Monday, December 08, 1997 5:07 PM
> >>
> >> >
> >> > The return line must have a min of pressure.
> >> > All gas tanks have a line at the bottom of the tank, for the pick-up,
> >> > and then various others, they can be mounted all over the place.
> >> > I beleive it was some Chry. where they had some mounted on the sides at
> >> > about what would be 7/8 full.  On some tanks there is a large trapped
> >> > air bubble, all I was making the point was not to let the return line be
> >> > covered, if the return is sometimes covered the return line pressure
> >> > goes up, the regulator can't bleed the pressure down, and the motor goes
> >> > very rich.
> >> >   Hope that better explains it   Bruce  nacelp at bright.net
> >> >
> >>
> >> I have heard that the return line must exit at the bottom of the
> >> tank, so there is no "fuel splash". I think I got this from the
> >> JTR book. Is this true? Does it matter?
> >>
> >> - Bruce
> >>
> >> --
> >> -----------------------------------------------------
> >> <<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> >> -----------------------------------------------------
> >>                  Bruce A. Bowling
> >>                  Staff Scientist
> >>    Thomas Jefferson National Accelerator Facility
> >>     12000 Jefferson Ave - Newport News, VA 23606
> >>                  (804) 249-7240
> >> bowling at cebaf.gov  http://devserve.cebaf.gov/~bowling
> >> -----------------------------------------------------
> >> <<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> >> -----------------------------------------------------
> >
> > Question: Isn't fuel vapor pressure a function of temperature or some
> such thing? And if that is the case, then with a closed system (as in the
> case of a gas tank with the lid on) the vapor would reach a certain
> pressure and remain at that pressure as long as the temp remained the same.
> Perhaps minor variations with sloshing, but always returning to the
> appropriate pressure for a particular tem.

  Yes, except that the fuel is heated by the engine.  If the fuel cap has no
pressure release built in, the tank can build much pressure.