Patrick,
Boy, you sure dazzled me with the numbers and the one that sticks in my
mind is the 18' max.! There might be 15' between the tank and the carbs.
horizontally, but the whole height difference between the tank and carbs is
about 2' maximum, and that is the important when pumping liquids.
I don't believe the placement of a fuel pump is all that important as all
my old Sunbeam Talbots have the mechanical pump on the engine as did most
cars of this era.
And then there were the vacuum tank pump systems of the 1920's that
operated by creating a vacuum in a tank mounted on the firewall of most
cars to suck the fuel from the tank. They worked fine as long as there was
vacuum!
Push or pull, it is your choice!
Later,
Bob
At 10:23 PM 2/11/99 -0800, you wrote:
>We've been going around a bit about the location of the fuel pump and I keep
>being bothered by the suggestion that pumps push and don't pull and should
>therefore be placed under the tanks. As a matter of semantics, irrespective
>of where it is placed, it will "pull" from one side and "push" to the other,
>but there may be good reason to place a pump low rather than high. When a
>fluid is moved from a low spot (the gas tank) to a high spot (a pair of
>Stromburgs or Solexs) whether it is pushed up the incline from below or
>pulled up to the top should not matter that much. But it does. A fluid,
>when pulled from the top is subject to volatalization and becoming vapor
>before it reaches the pump impellors. Most pumps do a great job of pumping
>fluid but a lousy one of pumping vapor. If pushing from below, they are
>merely subject to the maximum pressure they can produce.
>
>I looked it up and found some numbers that might interest:
>
>If we consider it to be a static system with no movement it is a matter of
>how high can you suck gasoline in a straw before you get a mouthfull of
>vapor instead of gas:
>The operative equation here is:
>
> Pair = Pgas + pgh
>
> air
> | |
> |__| _ height (h)
> | |
> | |
> |g |
> |a | straw
> |s |
> |o |
> |l |
> |i |
> |n |
> |e |
> ____|__|_____gasoline
> | |
> | |
>Where:
> Pair is the local atmospheric pressure (101.3 kPa)
> Pgas is the vapor pressure of gasoline ( 62.5 kPa)
> p is the density of gasoline (718.6 kg/m^3)
> g is the force of gravity ( 9.81 m/s^2)
> h is the height we are looking for ( m )
>
> 101.3 kPa = 62.5 kPa + (718.6 kg/m^3)(9.81 m/s^2)(h m)/(1000 Pa/kPa)
> 38.8 kPa = (7.05 kPa)(h m)
> h = 5.5 m or,
> h = 18 feet
>
>So this says we should be able to 'pull' gasoline up a vertical 18 feet
>before running into trouble, as our Alpines are about 13 feet from tip to
>tail, the distance between the tanks and the carburators should always be
>less than this even when parked some of our San Francisco streets. Of
>course this leaves out the discussion of head loss due to fluid flow and the
>variations in local atmospheric pressure.
>
>All this being said, I still think it is better to place it lower if
>possible. But if you cannot, or do not want to, the numbers say we should
>be OK.
>
>-Patrick
>SV, Richmond, CA
>
=========================================================
Robert (Bob) A.C. Hamilton, Waverley, Nova Scotia, Canada
The Man of Many Sunbeams - Alpine, Drophead and Saloon 1953-1954
Home Page: http://www.navnet.net/~hamilton/index.html
E-Mail: hamilton(at)cast.navnet.net
=========================================================
This archive was generated by hypermail 2b30 : Tue Sep 05 2000 - 10:35:13 CDT