Among my other interests I run a family owned 1929 4.5 litre Bentley. The
fuel gauge on this beast runs on a very similar principle. Sothere is not
much new in the world.
An inverted cylinder is installed in the fuel. The concave bottom of the
cylinder is open to the fuel and a capilary line runs to a manometer on the
dash. Thereby allowing a readout of fuel level.
To circumvent the problem of disolving air there are a series of trays
arranged up the outside of the cylinder with pipes to below the cylinder
which catch splashes of fuel and drain them and air bubbles to the bottom
and therefore replenish the system with air. If any body is confused by
this (and I am sure they are) will fax anyone the drawings.
The system relies on a vehicle with 1929 suspension being driven on a 1929
road surface to bounce the fuel around violently enough to create enough
air to keep the system primed. Then I believe that after a night in the
garage the gauge read zero until you had driven for a while. I don't know
because I have never got the damn thing to work.
Incidently the version supplied to Rolls Royce had a seperate hand pump on
the dash to prime the system with air.
FWIW the Bentley owners I know think the system rates between not very good
and bloody awful - although I am sure that an ASI based device would be
somewhat better.
About the air being saturated with fuel - I don't think this is the
problem. The problem is of the air dissapearing into the fuel not vice
versa. There is a lot of fuel and not much air to dissolve into it.
I hope the information is useful and not too negative.
Regards
Ben
>o>Well that stirred up a bit of interest, which encourages me to add a bit
f the background...there is really quite a lot of physics to be thought
>about and I have done some experiments to verify some of the effects.
>
>RonSwinden@aol.com writes:
>
><< Will the air column in the "pitot" line gradually "disolve" into the
>petrol >>
>
>The "dissolving" stops at saturation, so firstly- is there a difference in
>behaviour between petrol free air and one saturated with vapour ? There
>probably is, but as long as it is constant it would not matter. Very little
>volume of liquid is required to saturate the air in the tube (22 litres
---From a
>gram.mol if I remember rightly) so even if it came from the surface of the
>fuel which first seals off the tube, the level change would not be seen.
>Secondly the tank is likely to have unusable fuel in the bottom and thus the
>tube will be full of saturated air even if you start from empty. But I would
Ben Greenhalgh
email ben_g@sol.co.uk
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