Posted by frank (126.96.36.199) on October 10, 2005 at 10:44:27:
In Reply to: sa750 fuel tank question. posted by Randy on October 10, 2005 at 08:52:28:
Those 3 "venting" outlets on the top fwd part of the tank are really only 2 vents (uprght/inverted) plus one inlet for an upper wing tank.
We use our flop tube as the only feed source from the tank. The other bottom nipple should be for an overboard drain valve.
To confuse the issue though - we were never able to solve the upright-flight overboard venting puzzlement with our tank. Seems we had visible venting from the tank while inverted (via the vent line that runs up the R/H cabane). With both vent lines then adjusted and tweaked to balance pressures we still had "stealth" upright venting to the belly/overflow vent line. This was evident from fuel consumption/loss on xc hops and finally confirmed by several formation flights with the wingman watching the belly vent. Blowing into either vent would bubble air up thru the fuel in the tank???
Never could get that totally solved so just had the tank venting changed over to the simple Eagle type attached to the fill spout. With our tank opened for that job, the experienced A&P acro builder/welder said he could not puzzle out the routing and function of vents in our original tank since both upright and inverted vents ran to the bottom???
My surmise is that the orignal venting was installed incorrectly and flying mostly 20-25 minute hops we just never perceived the problem until recently. Perhaps we simply confused and cross-plumbed those three upper nipples at a prior tank removal for leak repairs?? Perhaps it was related to the extraneous 5" length of aluminum fuel tubing found in the tank (along with a fuel sampler/screwdriver) when we first removed the tank about 5 years ago. Will now never know for sure.
Just another item in our long list of rebuilding the Gold Duster!
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