REFLECTOR: Re: Check valves in fuel vents
KeithHallsten
KeithHallsten at quiknet.com
Mon Feb 28 20:35:35 CST 2005
Brett,
The atmospheric pressure drops with altitude. However, the vapor pressure
of gasoline varies only with temperature. Therefore, the margin between the
two drops with altitude. At the extreme (which is not an issue for us), the
gas will boil off in the tanks and the vapor will escape out the vent(s).
Our situation is not so extreme, but you can see that there is a decreasing
pressure differential available to open a check valve.
Keith Hallsten
----- Original Message -----
From: "Brett Ferrell" <bferrell at 123mail.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Monday, February 28, 2005 3:29 AM
Subject: Re: REFLECTOR: Re: Check valves in fuel vents
> 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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