REFLECTOR: Re: Check valves in fuel vents

Scott Derrick scott at tnstaafl.net
Mon Feb 28 10:40:46 CST 2005


If your that worried about ice, do what the type certificated planes 
require.

A heated fuel vent..

Scott

KeithHallsten wrote:

>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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