The extra hole could be plugged up also, given enough wet stuff kicked
up by the tire, worse if it freezes aloft. The concern I thus have is
that a vent for a single tank requires a fail-safe (i.e., the extra
hole) that must work under all conditions, or fuel starvation results.
I have no sight gauge, so I'll have no redundancy there (presuming
it's adequate, given the restrictor in the line). Of course I need no
approval, so FWIW, I did this: My vent tube is in the leading edge of
the vertical fin (for aesthetics), and the line runs from there to a
generous water trap, located behind the trim mechanism inspection
cover. From there, it goes to the area near top of the filler neck
(classic style, top mount). At that point, I installed a check valve
I made from a 1/4" nylon, compression-fitting "T" connector. The
unused connector contains the check valve, made from a small ball,
spring, and some epoxy which both caps off the nylon hex nut and is
the ball seat. A hole drilled through the epoxy ball seat is the
fail-safe vent. The nut has RTV on the threads, and turning it
adjusts the vacuum needed to unseat the ball. From there, to the tank
vent. Appears to work just fine. Sound OK? The only thing I can
think of is that some small amounts of fuel vapor could leak past the
valve into the aft fuselage, but I can run a vent line from the check
valve to the outside easy enough, like downstairs to the flap tube
slot.
Regards,
Fred F., A063, N3EU
Roger Sheridan wrote:
>
> Dear All,
>
> Am keen to elicit any opinions on siting the fuel tank vent underneath
> rather than on top as per the manual. Has anybody done this successfully
> and/or obtained PFA approval?
>
> Sight gauge syphoning needs to be avoided, why not link the sight gauge vent
> and tank vent? I think that should prevent syphoning. (My seat back sight
> gauge doesn't go up to the roof)
>
> Rain entering the tank should be avoided.
>
> Vent underneath would be more prone to blockage by dirt/mud but the extra
> drilled hole should prevent total blockage.
>
> Any opinions gratefully received!
>
> Cheers,
>
> Rog Sheridan.
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