REFLECTOR: fuel feed - my solutions
Brett Ferrell
bferrell at 123mail.net
Mon Feb 28 21:13:58 CST 2005
Keith -
I was under the impression that Jim didn't think that the tank would be
under vacuum if there was no venting, and the below are several relevant
sites that show this is, in fact, the case, whether there is a pump attached
or not. Once you get past the question of whether the tank would be subject
to vacuum or not, the question of whether the check valve helps becomes
trivial. Any atmospheric pressure versus near vacuum will open the valve,
so I consider it relevant.
Brett
----- Original Message -----
From: "KeithHallsten" <KeithHallsten at quiknet.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Monday, February 28, 2005 9:54 PM
Subject: Re: REFLECTOR: fuel feed - my solutions
> Brett,
>
> Not only is that NOT analysis, it's not even relevant. No one has
> proposed
> eliminating all vents from the fuel system! We are discussing whether the
> check valve will actually work to provide an adequate vent!
>
> Keith Hallsten
>
>
> ----- Original Message -----
> From: "Brett Ferrell" <bferrell at 123mail.net>
> To: <reflector at tvbf.org>
> Sent: Monday, February 28, 2005 12:53 PM
> Subject: Re: REFLECTOR: fuel feed - my solutions
>
>
> 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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