the fuell would push the inlet valve closed Glenn
On Apr 24, 2010, at 12:21 PM, Donald wrote:
I think perhaps that only ONE check valve would need to fail John.
If this pump is like most every other fuel pump, the check valves
are identical but e reversed from each other, allowing the diaphram
to suck thru the one on the wing tank side, and then on the push
stroke push it into the tank, with the suction side pushed shut.
They are so lightly sprung, that the fuel pressure of the elevated
tank would flow past the (now defective) outflow valve, and easily
push the inlet valve open. Just a thinking statement, not proven.
Thanks for the excellent drawing, helps even more!!
--- In [email protected], John Cooper <j...@...> wrote:
>
> On 4/24/2010 10:50 AM, Donald wrote:
> > Now, I FINALLY understand the system.
> >
> In case anyone else is still pondering this, I've attached a drawing
> that should clarify things. The normal fuel level in the tank is
to the
> green line. Fuel from the pump comes in from the higher (left) of
the
> two fittings, so, should the line from the pump rupture or burn
through,
> fuel will not siphon back to feed the fire. Fuel from the overflow
> fitting (right) goes back to the wing tanks only when the level
exceeds
> the normal level. Fuel to the engine feeds from the bottom of the
tank
> (not shown).
>
> In order for fuel to get back to the wings and leave the level
anything
> less than the normal level, there would have to be a break in the
> fitting, say near the bend of the elbow, in which case fuel could
leak
> back, but only to the level of the break. Note too that a leak on
the
> pump fitting should not have any effect as there are 2 check
valves in
> the pump, both of which would have to fail in order for fuel to
make it
> back to the wings.
>
> As Ed mentioned, there are some tanks, Ternplate, I think, that
have a
> compression fitting in the bottom through which a tube passes. This
> tube is supposed to extend up to near the top of the tank and
form the
> stand pipe. These tubes are known to break and cause fuel to leak
back
> to the wings. My original statement that fuel cannot leak back to
the
> wings presumes nothing is broken, or, as I said, if it happens,
> something is wrong.
>
> HTH
>
> --
> John Cooper
> Skyport East
> www.skyportservices.net
>
