REFLECTOR: fuel feed - my solutions

[Scott Baker]

Hi Scott,
Natalie will know the part # (I don't, offhand).  Also - a correction to my 
earlier note to Keith about the likelihood of discovering a blocked vent 
line due to mud-dobbers - I meant to say - it would probably NOT be 
discovered because it is such a pain in the arss to low crawl under the 
fuselage and make a thorough inspection.
SB

----- Original Message ----- 
From: "Scott Derrick" <scott at tnstaafl.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Monday, February 28, 2005 11:53 AM
Subject: Re: REFLECTOR: fuel feed - my solutions


> 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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