I think since fuel is being lifted out of the tank by suction (drawing a
vacuum), that it is good engineering practice to size the suction line a size
bigger than the pressure line, to ensure enough fuel will be present at the
inlet of the pump to avoid vapor lock or pump cavitation problems under high
demand conditions.
No matter if its gas, oil, or water or some other liquid, pumps drawing on
anything needing suction lift usually have the suction line bigger.
I can get out my engineering rule of thumb equations and try to prove it
mathamatically, but "good engineering practice" is a lot easier.
Best Regards,
Jim
Chesapeake
Virginia
> From: aultgc@att.net
> To: 9laser3@bright.net; eddietude@socal.rr.com
> Date: Mon, 23 Feb 2009 20:30:21 -0600
> CC: datsun-roadsters@autox.team.net
> Subject: Re: [Roadsters] Fuel Line size
>
> Paul,
>
> Gasoline is essentially incompressible, so the fuel pressure will not
> contribute to a difference in pressure loss upstream and downstream of the
> pump. Differences in fluid velocity will, but I doubt that the use of the
> same size line upstream and downstream of the pump will make any difference
> in fuel delivery. But then, I'm not the engineer who designed the system,
> so what do I know? Why the difference in line size? Beats me.
>
> Gary
> ----- Original Message -----
> From: "Paul" <9laser3@bright.net>
> To: "'Eddie'" <eddietude@socal.rr.com>; "'Gary and Cindy Ault'"
> <aultgc@att.net>
> Cc: "'Datsun Roadster List'" <datsun-roadsters@autox.team.net>
> Sent: Monday, February 23, 2009 6:20 AM
> Subject: RE: [Roadsters] Fuel Line size
>
>
> > The fuel from the tank to the pump is not under pressure so it requires a
> > larger diameter. Past the pump, it's pressurized to the carbs.
> >
> > Paul (Just a guess?)
> > Ohio
> >
> > -----Original Message-----
> > On Behalf Of Eddie
> >
> > IT doesn't make much sense to have varying thicknesses in the fuel line,
> > because the least sized section determines the MOST amount of fuel flow.
> >
> > But, thanks for the info. Do you have the metal line measurements in
> > fractions?
> >
> > Eddie
> >
> > Gary and Cindy Ault wrote:
> >> Eddie,
> >>
> >> The fuel line (metal line from the tank) in my '66 measures 0.265
> >> inches OD; the brake lines measure 0.195 inches OD. All lines are
> >> original.
> >>
> >> The rubber fuel line from the filter to the pump is 5/16-inch ID, and
> >> the rubber line from the pump to the carbs is 1/4-inch ID. Why the
> >> difference, I have no clue.
> >>
> >> Gary
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