Agreed that there's logic in the PFA's requirement for the return line to
go into the top of the tank. However, if the necessary restrictor in the
vapour return line were to be placed just behind the firewall (instead of
being on the engine-side), then any rupturing of the line forward of that
position would feed very little fuel.
As I understand it (from Andair, who make two versions of non return
valve), where a valve is inserted in a vapour return line then it also
needs a bleed orifice in the valve. In which case there's little point in a
valve; just have the orifice.
Duncan McFadyean
On Monday, April 29, 2002 2:01 PM, John Cliff
[SMTP:john@crixbinfield.freeserve.co.uk] wrote:
> > Graham, Why do we want to put the fuel return up at the vent fitting
rather
> > than down at the reserve side fuel outlet?
> > Kevin A211
>
> I had 'discussions' with PFA Engineering about this when putting in a
mod to
> replumb the fuel system in aluminium.
>
> They don't seem all that happy about returning the fuel to the bottom of
the
> tank because of the possibility of immediate recirculation - returned
bubbles
> finding their way almost immediately back to the feed in use, though
clearly
> they have sanctioned the arrangement the factory uses. Whether this
would ever
> happen in practice seems dubious.
>
> The reason they preferred the return line to go to the vent boss at the
upper
> rear of the tank is that in the event of a serious engine room fire which
> consumed the fuel flexible hoses, the unvalved return line could feed the
entire
> tank contents into the fire. With the high level return this will not
happen ,
> unless you are in an unusual attitude. So this is what I have done.
>
> John Cliff
> #0259
>
>
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