REFLECTOR: Re: Check valves in fuel vents
Brett Ferrell
bferrell at 123mail.net
Mon Feb 28 05:29:53 CST 2005
Unless you have a nuclear reaction in there, whatever fuel leaves the tank
must be replaced by air or something, or a vacuum will be drawn on the tank.
One atmosphere at sea level is about 14.7 psi, and at altitude there's still
postive pressure of a few pounds (depending on how high you are), and that
would be present in the cabin and pushing against the open/exposed side of
the check valve. Thus it would have the required opening differential
required if the primary vent were plugged.
Brett
----- Original Message -----
From: "Jim Sower" <canarder at frontiernet.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, February 27, 2005 10:20 PM
Subject: Re: REFLECTOR: Re: Check valves in fuel vents
<... you still have several psi of atmospheric pressure versus vacuum ...>
WHAT vacuum? Where is that vacuum coming from? And of course at 20k
you have less than half an atmosphere pushing.
Jim S.
Brett Ferrell wrote:
> A check valve in the fuel line very likely will not open reliably, it sees
> the fuel head, which is small; but a check valve in the vent line will in
> my opinion open reliably, even at 20,000 feet you still have several psi
> of atomospheric pressure versus vacuum.
>
> Brett
>
> ----- Original Message ----- From: "KeithHallsten"
> <KeithHallsten at quiknet.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Sunday, February 27, 2005 5:08 PM
> Subject: REFLECTOR: Re: Check valves in fuel vents
>
>
> Jim,
> You have sucessfully made the point that I was trying to make with my
> posts
> regarding the cracking pressure of "alternate vent" check valves. I have
> a
> strong suspicion that most such installations will not function as the
> builder intends. The pressures (above or below ambient) in the fuel and
> vent system (upstream of the fuel pump) are so exceedingly small that I'm
> not aware of any check valves that would be appropriate. If you find a
> check valve with a sufficiently low (nearly zero) cracking pressure, it's
> unlikely to be reliable. I really think we have to face the fact that a
> Velocity has no place in an icing environment, and not imagine that we can
> mitigate the effects of ice on the fuel vent.
> Keith Hallsten
>
>
> ----- Original Message ----- From: "Jim Sower" <canarder at frontiernet.net>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Sunday, February 27, 2005 12:53 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
>> >
>> > ----- Original Message -----
>> > *From:* Brian Michalk <mailto:michalk at awpi.com>
>> > *To:* Velocity Aircraft Owners and Builders list
>> > <mailto:reflector at tvbf.org>
>> > *Sent:* Saturday, February 26, 2005 10:01 AM
>> > *Subject:* RE: REFLECTOR: fuel feed - my solutions
>> >
>> > McMaster has a lot of check valves.
>> > This one says less than .5 PSI cracking pressure.
>> > The image
>> > “http://www.mcmaster.com/catalog/111/gfx/large/47245kp1l.gif”
>> > cannot be displayed, because it contains errors.
>> > http://www.mcmaster.com/catalog/111/gfx/large/47245kp1l.gif
>> > This one says 0 PSI cracking pressure.
>> > The image
>> > “http://www.mcmaster.com/catalog/111/gfx/large/7909kp1l.gif”
>> > cannot be displayed, because it contains errors.
>> > http://www.mcmaster.com/catalog/111/gfx/large/7909kp1l.gif
>> > These came from this page:
>> >
>> > http://www.mcmaster.com/nav/enter.asp?pagenum=389
>> >
>> >
>> >
>> > Brian Michalk <http://www.michalk.com>
>> > Life is what you make of it ... never wish you had done something.
>> > Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
>> > musician, home-brewer, entrepreneur and barely single
>> >
>> >
>> > > -----Original Message-----
>> > > From: reflector-bounces at tvbf.org
>> > [mailto:reflector-bounces at tvbf.org]On
>> > > Behalf Of Chuck Jensen
>> > > Sent: Saturday, February 26, 2005 4:27 AM
>> > > To: Velocity Aircraft Owners and Builders list
>> > > Subject: RE: REFLECTOR: fuel feed - my solutions
>> > >
>> > >
>> > > Jerry,
>> > > All check valves has some pressure differential which we can ill
>> > > afford to loose when the fuel head is measured in inches.
>> > > Probably the strongest reason for leaving them off is if you do
>> > > have a little non-uniform fuel flow during your flight, at least
>> > > when you land, the tanks will self level for your next
>> > > flight--assuming your on the level when you parked.
>> > >
>> > > Chuck
>> > >
>> > > -----Original Message-----
>> > > From: reflector-bounces at tvbf.org
>> > [mailto:reflector-bounces at tvbf.org]On
>> > > Behalf Of Jerry.Brainard at anthem.com
>> > > Sent: Friday, February 25, 2005 5:22 PM
>> > > To: Velocity Aircraft Owners and Builders list
>> > > Subject: Re: REFLECTOR: fuel feed - my solutions
>> > >
>> > >
>> > >
>> > > Just because I don't know - is there a reason not to put a check
>> > valve in
>> > > line on the strake feed lines? My thought is that this would
>
> prevent
>
>> > > retrograde flow into a tank that is on the low side (out of rig)
>> > or has a
>> > > leaking cap. I can think of many scenarios where one might be
>> > confused as
>> > > to what is happening, but it would seem to resolve any issue
>> > with pulling
>> > > fuel into a tank from the feed line. Of course there is also
>> added
>> > > complexity and another failure mode to consider.
>> > >
>> > > -jerry
>> > >
>> > > 513-484-1328
>> > > 513-336-5949
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > Don19dw at aol.com
>> > >
>> > > Sent by: To:
>> > > reflector at awpi.com
>> > >
>> > > reflector-bounces cc:
>> > >
>> > > @tvbf.org Subject:
>> > > REFLECTOR: fuel feed - my solutions
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > 02/25/2005 04:38
>> > >
>> > > PM
>> > >
>> > > Please respond to
>> > >
>> > > Velocity Aircraft
>> > >
>> > > Owners and
>> > >
>> > > Builders list
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > As a result of my accident in June 1999, caused by a leaking
>> > fuel cap, I
>> > > made the following changes.
>> > > 1) Added the sump tank "low fuel" warning system per Velocity
>> > > plans, except
>> > > located float slightly lower. The "low fuel" warning would have
>> > allowed we
>> > > to reach an airport prior to fuel exhaustion from right tank and
>> > sump
>> > > tank.and thus prevented the accident.
>> > > However then during later flights, especially in turns would get
>> > flashing
>> > > "low fuel" warnings which made me very nervous. To trouble shoot
>
> the
>
>> > > problem I removed the rear seats and spar cover so I could
>> > visually see
>> > > sump tank in flight. Using "T" fittings I added a vertical clear
>> > > sight tube
>> > > between top sump vent port and bottom outlet port plus a light
>> > shinning on
>> > > the tube to see fuel level from my pilots seat. As Scott Swing
>> > suggested,
>> > > the sloshing of the fuel in the sump tank was causing the
>> > flashing "low
>> > > fuel" warning with little or no lowering of fuel level.
>> > > 2) In order to solve flashing "low fuel" warning, I added a time
>> > delay
>> > > relay set at 6 seconds, before warning light went on, and have
>> > > not had that
>> > > problem since.
>> > > 3) Installed a manual shut off valve in fuel line from each
>> > strake into
>> > > sump tank. These left and right shut off valves are actuated by
>> > cables and
>> > > small levers on each side of keel at pilots hip. These valves
>> > > could be used
>> > > in flight to isolate either strake tank from the sump if the
>> > fuel level in
>> > > one side or the other is seen to be dangerously low. If the sump
>> > vent is
>> > > closed, the fuel pump should "suck" fuel from the open fuel
>> > > strake. However
>> > > the argument for a closed sump vent is valid "to suck fuel" only
>> > if empty
>> > > tank is shut off, otherwise air is "sucked" from the empty tank,
>> > rather
>> > > than fuel sucked from the other tank. That apparently is what
>> > happened
>> > > prior to my accident. So far have never used my added valves in
>> > flight.
>> > > (However these valves are handy during servicing and I recommend
>> > adding
>> > > them for that reason alone)
>> > > 4) Added an instrument panel note: " Warning: at least every 30
>> > minutes,
>> > > check fuel level in each strake tank. If an unusual balance is
>> > > seen, ASSUME
>> > > fullest tank is unusable"
>> > > 5) After rebuilding the airplane, discovered the turn and bank
>> > > indicator in
>> > > the instrument panel, was not installed vertical, about 1/2
>> > bubble off
>> > > vertical. Once that was corrected, had to shim left rudder out
>> > 1/4 inch at
>> > > trailing edge. Plane now flies perfectly level and straight and
>> > have not
>> > > had any unusual fuel level problems since.
>> > > 6) Finally check fuel caps are tightly closed and properly
>> > lubricated.
>> > >
>> > > This may have been suggested to Jim already. During flight, have
>> > you held
>> > > slight pressure on one rudder or the other, to see if fuel tank
>> > levels
>> > > equalize? If that occurs, then I strongly suspect plane is not
>> > flying
>> > > perfectly level and straight.
>> > > Don White N19DW XL/RG
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