REFLECTOR: fuel feed - my solutions

[Scott Derrick]

Scott,

My 96 RG does not have a fuel vent check valve. 

Do you know the part number, or will Natalie know what I'm talking about?

Scott

Scott Baker wrote:

> Wait a minute ... I don't think the factory has made any such 
> statements, implied or otherwise.  Brett Ferrell has it figured out 
> exactly right.  The alternate fuel vent check valve will open the 
> moment fuel is delivered to the engine via the fuel pump.  Theorize 
> all you want, the alternate fuel vent check valve works.
> SB
>  
> ----- Original Message -----
> From: "Jim Sower" <canarder at frontiernet.net 
> <mailto:canarder at frontiernet.net>>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org 
> <mailto:reflector at tvbf.org>>
> Sent: Sunday, February 27, 2005 10:16 PM
> Subject: Re: REFLECTOR: fuel feed - my solutions
>
> > <... 1 atmosphere versus vacuum will open nearly any check valve ...>
> > *Of course* a vacuum will open a check valve.  Nobody's arguing that. 
> > The (false) implication from the factory, etc. is that the head 
> pressure
> > of the fuel gravity feeding the fuel pump would open it, which it
> > clearly would *not*.  The fuel pump would clearly *suck* it open, but
> > that would put an underpressure at the pump inlet.
> >
> > I guess it was on another list that we went into so much detail around
> > vapor lock which is not a real issue here (unless somebody is 
> interested
> > in a recirculating MPFI engine (auto conversion)).  However, if you 
> have
> > a vented sump tank, pretty much any check valve alive would prevent
> > gravity flow to the sump, and you would be left with < 5 gal usable
> > fuel.  Actually, you'd probably be under 3 gal and clueless as to the
> > actual amount you had by the time you figured out that the low-sump
> > indication was for real).
> >
> > I think it's a recipe for disaster and you won't see it coming ... 
> Jim S.
> >
> > Brett Ferrell wrote:
> >
> >> As soon as the pump pulls some fuel out of the sump with a blocked
> >> vent line, the check valve will open and vent some air into the
> >> tanks.  1 atmosphere versus vacuum will open nearly any check valve. 
> >> I've done some process safety work and seen industrial tanks collapsed
> >> from under-pressure, and I think it would be foolish not to install
> >> the factory-recommended check valve and allow your tanks to routinely
> >> run under vacuum.
> >>
> >> Brett
> >>
> >> ----- Original Message ----- From: "Jim Sower" 
> <canarder at frontiernet.net <mailto:canarder at frontiernet.net>>
> >> To: "Velocity Aircraft Owners and Builders list" 
> <reflector at tvbf.org <mailto:reflector at tvbf.org>>
> >> Sent: Sunday, February 27, 2005 3:53 PM
> >> Subject: Re: REFLECTOR: fuel feed - my solutions
> >>
> >>
> >> My figures indicate that .5 psi is the equivalent of about 165 
> kias. Bad
> >> news: they aren't going to vent a damned thing if the vent ices over.
> >> Good news: the fuel pump will generate plenty enough suction to 
> overcome
> >> that (of course that underpressure would add to your chances of vapor
> >> forming in the vent line and/or cavitation at the pump face).
> >> Check valves are not the panacea some folks would have you believe ...
> >> Jim S.
> >>
> >> Wayne wrote:
> >>
> >>> I'm using two of the .5 jobs for an alternate air source in the top
> >>> of the loop before the vent line goes to the bottom of the fuselage.
> >>> If the fuel vent iced over I hope they will provide cabin air to the
> >>> fuel tanks. If the bird is upside down they shouldn't allow fuel to
> >>> leak inside the cabin.
> >>> Wayne
> >>>
> >>
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