REFLECTOR: fuel feed - my solutions

[Brett Ferrell]

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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