REFLECTOR: fuel feed - vent check valve

[Ron Brown]

I'll find out this week.  My annual condition inspection is due right now.  I need to drain my fuel tanks - while I am at it - I will plug the vent line and see if the AS&S fuel check valve will open to allow the fuel to continue draining.

Re cabin pressure, I have found that my cabin pressure is essentially the same as my static port - no measurable change in altitude or airspeed indications when opening the static valve to the cabin.  I have an RG and I have the factory exhaust vents installed over my bottom wing bolt access holes.  

Ronnie
  ----- Original Message ----- 
  From: Brett Ferrell 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Monday, February 28, 2005 6:24 AM
  Subject: Re: REFLECTOR: fuel feed - my solutions


  I actually don't have anything riding on it, because if I need the check valve to open, my primary line is already plugged, and the factory-recommended supplemental vent check valve can only *help*, not hurt the situation.  I haven't done any calculations on it, but I do have an engineering degree and have done process safety studies, and I don't ever want my tanks to be unvented, if possible.  The mass of fuel leaving the tanks needs to be replaced with an mass of air of like volumne, or a vacuum will begin to be drawn on the tanks and potentially cause thier failure or cavitation at the pump, neither of which is desirable in my view.  I just wanted folks to hear a voice saying that they believe the factory design is a sound one, in addition to all of the talk of modifications.  I believe it is, and that's what I'm installing.  I'll leave the math to those changing that design.

  Brett
    ----- Original Message ----- 
    From: Jim Sower 
    To: Velocity Aircraft Owners and Builders list 
    Sent: Sunday, February 27, 2005 10:29 PM
    Subject: Re: REFLECTOR: fuel feed - my solutions


    Brett Ferrell wrote:

      I don't avodcate sucking the fuel, but if you're drawing 15 gph, I don't believe the fuel is going to off-gas fast enough to fill the void, warm or not, so I don't believe that partial pressure will keep the check valve from opening and venting the tank. 

    Do you have anything like say, physics or math to support that postulation?
    I hope so.  You've got a lot riding on it ... Jim S.


      Brett 
      ----- Original Message ----- From: "Al Gietzen" <ALVentures at cox.net> 
      To: "'Velocity Aircraft Owners and Builders list'" <reflector at tvbf.org> 
      Sent: Sunday, February 27, 2005 6:29 PM 
      Subject: RE: REFLECTOR: fuel feed - my solutions 



        Subject: Re: REFLECTOR: fuel feed - my solutions 

        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 

        Of course you don't really have that option since warm avgas has a vapor 
        pressure of around 8-9 psi, and warm mogas 10-12.   Which means at _______ 
        ft, you have no "suction". 
        That's why you don't want to depend on sucking fuel anywhere. 

        Al 

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