REFLECTOR:Low fuel light & Vent System

[Brett Ferrell]

OK, granted, that is how I read that.

But I still think the sump should be vented personally, as don't understand
what condition could cause air to flow into the sump and displace a
heavier/denser fluid (fuel). That doesn't happen without some reason.

I don't think you're going to flow fuel uphill into the strakes unless
you're pulling A LOT of vacuum through the caps, so the only other
explanation is the fuel pump is draining the sump faster than the strakes
supply it.  In this situation, the unvented sump would experience a vacuum
and (potentially) rupture.  My limited understanding was that in a turn the
uphill wing would/should still be able to provide adequate fuel flow to the
sump/engine, but it would seem reasonable that this strake could provide
fuel as quickly as the downwind wing 'steals' fuel from the sump.  It's
problably not practical, but it would be interesting to put fuel flow
instruments in each strake line, and a site glass in the sump vent in order
to test these assumptions.

Brett

----- Original Message ----- 
From: "KeithHallsten" <KeithHallsten@quiknet.com>
To: <reflector@tvbf.org>
Sent: Wednesday, July 23, 2003 11:12 PM
Subject: Re: REFLECTOR:Low fuel light & Vent System


> Brett,
> I think you misunderstood my proposal!  I'm not shutting off the entire
vent
> system!  The sump tank will still be vented through the 3/8" fuel lines,
> strakes, and strake vents bback to the manifold, so there won't be any
> significant flow restriction or tank crushing going on.
> Keith
>
>
> ----- Original Message ----- 
> From: "Brett Ferrell" <bferrell@123mail.net>
> To: <reflector@tvbf.org>
> Sent: Wednesday, July 23, 2003 6:46 PM
> Subject: Re: REFLECTOR:Low fuel light - NO!
>
>
> > Please, please, please do not do this (install a vent shutoff valve)!
Air
> must enter the system as the fuel drains out or 1 of 2 really bad things
> will happen.
> > 1)  Pop-Bottle plug effect - where the gas glug-glug-glugs to your
engine,
> or stops altogther as air cannot replace the lost fluid-or-
> > 2)  The tanks will crush as the fuel pulls vacuum on the tank and the
> outside air pressure pops the strake open
> >
> > Having seen a 30,000 industrial tank get crushed like a soda can from a
> plugged vent & overflow line, I'm horrified by the idea of this happening
in
> flight.  Allowing air into the tanks is the primary purpose of the vent,
and
> why you should install the check valve to allow cabin air into the tanks
> (but no gas-vapor into the cabin) should the external vent get blocked by
> ice.
> >
> > If there's an adequate fuel level in the stakes, an air bubble should
not
> be able to form in the sump, as the head pressure from the strakes should
> fill it to the level (in the vent line) of the strakes (fluids seek their
> own level and all).  If a bubble were to form it would indicate that the
> fuel pump is pulling the level faster than the tanks can replenish it.
> >
> > Brett
> >
> > Quoting Bob Kuc <bkuc1@tampabay.rr.com>:
> >
> > > Re: REFLECTOR:Low fuel light
> > > I was think about that also.  However, if you are on
> > > the low side of > fuel and then make a turn, the fuel on the inboard
> > > stake would rush to > the end.  Would that not introduce air into the
> sump
> > > tank that you would > have no way of relieving because you have the
vent
> > > blocked off?
> > >
> > > Bob
> > >   I plan to install a manual vent shut-off valve
> > > between the sump tank > and the vent manifold.  The result will be
that
> the
> > > vent system can > allow the main strake tanks to drain, but can't
> > > introduce air into the > sump tank.  I have a theory that the vent
line
> to the
> > > sump tank causes > more problems than it solves, once the initial
"burp"
> > > of air is allowed > to escape from the sump tank (before engine
start).
> > >
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