REFLECTOR: fuel feed - my solutions

[Brett Ferrell]

Quoting Jim Sower <canarder at frontiernet.net>:

>  I would welcome less sweeping, unsupported generalities and more of
> a point by point rebuttal of my math, my physics or my analytical
> methods.
>
>  I hope we can abandon rhetoric in favor of rational engineering
> analysis ... Jim S.

Here's a good article about tank failure to due pumpout at a nuclear powerplant:
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/circulars/1977/cr77010.html

Here's a discussion on how not to collapse your hot water heater due to
draining:
http://www.terrylove.com/wwwboard/messages/8816.html

Here's a warning from a tank supplier about the need for a properly sized vent
(to match the drain rate):
http://www.jvnw.com/techtip.html?main=techtip-scroll.html

Here's a article about Range Rover tank collapse to due blocked vents:
http://www.rangerovers.net/repairdetails/fuelpump.htm

Here's a article on Chrysler's requiring a vented fuel cap to avoid collapse:
http://www.imperialclub.com/Repair/Fuel/tank.htm

Here's a fuel-tank.com discussion of drain protection:
http://www.fuel-tanks.com/spcc.htm

Is that sufficient analysis?

Brett

>          ----- Original Message -----    From: "Jim Sower"    To:
> "Velocity Aircraft Owners and Builders list"    Sent: Sunday,
> February 27, 2005 10:16 PM   Subject: Re: REFLECTOR: fuel feed - my
> solutions
>       >
>  > *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"
>  >> To: "Velocity Aircraft Owners and Builders list"
>  >> 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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