As you and John pointed out, you are quite correct. No way it could happen unless BOTH valves failed. Jeez, and they let guys like me work on airplanes! Wish I could delete that post!
--- In [email protected], Glenn Putnam <putp...@...> wrote: > > 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 <john@> 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 > > > > > > > >
