tanks draining unevenly (again)

[ken nougaret]

Since day 1 my LH tank drained before the RH. I now have 50hrs on my SS7. Today my wife said "how about swapping caps from side to side". What a good idea. The RH now drained just like the LH did before. So should i assume that the non-draining cap is not sealed as well? Ken

[airlina]

Ken, could be tank seal, or it also could be the vent tube alignment to the relative wind inflight. The offending cap tube may need a slight bending to align it better. Bruce N199CL

[ken nougaret]

I dont think it is alignment of the tube because of how perfectly the issued followed from left to right. But i am keeping an open mind to that possibility.

[rv9ralph]

Ken, the only thing that changed from left to right was the caps... and the issue followed. Your caps are where the issue is. The vent tube adds a slight pressure to the tank. If the vent tubes are not aligned into the airstream, one tank will get more pressure than the other, thereby increasing the flow out of that tank.

The only other thing that could be different is the flow of air through the vent tube may not be the same due to a partial blockage, either debris or the hole through the cap is not the same size, or some other restriction.

Hope this helps.

Ralph

[jiott]

I think it is the alignment of the tube with the airstream, but also is affected by the cap seal. Here's why: those vent tubes definitely produce a small positive pressure in each tank, probably different in each one due to the spiraling air flow, which in turn causes each tank to drain at a slightly different rate. However, if the rubber cap seal is leaking, that would cause some of the ram pressure from the vent tube to leak out the cap seal and slightly reduce the positive pressure in that tank, and therefore the drain rate. I would make sure the cap seal is good, then tweak the tube alignment to get fairly even drain rates.

I know for a fact that if I am careless about flying with the ball centered my drain rates get uneven. With ball centered and wings level my drain rates stay fairly even, never perfect. I have tweaked some with the vent tube alignment. I also installed the Mercedes Benz blue rubber cap gaskets.

[Esser]

Switch your seals and see if the problem follows that.

[ken nougaret]

It seems i have fixed the problem. I tapped the fuel cap tabs up to make for a tighter cap fit. I drain evenly now!