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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