Mailing List lml@lancaironline.net Message #58308
From: Bill Harrelson <n5zq@verizon.net>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Fuel restriction or air?
Date: Wed, 18 May 2011 08:42:33 -0400
To: <lml@lancaironline.net>
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Good point, Bill. The check valves supplied by Lancair for the vent system on my IV are free flowing inward and “somewhat” restricted flowing outward. This prevents venting a lot of fuel overboard while taxiing with full wing tanks (no winglets) yet allows air to escape at a relatively slow rate to avoid the problem that you describe. Certainly, a normal one way valve (free flow one direction – no flow in the other) should NOT be used on a vent system.
 
Bill Harrelson
N5ZQ 320 1,900 hrs
N6ZQ  IV under construction
 
 
 
 
Sent: Wednesday, May 18, 2011 7:43 AM
Subject: [LML] Fuel restriction or air?
 

 

{Did you verify the fuel vents are working properly?   ....and that the check valves on the vents are oriented correctly?}

 

There should be no check valves on vent lines. If you take off at sea level with a wing tank at atmospheric pressure, 14.7 psia trapped by a check valve, and climb to 18,000 feet, static pressure 7.35 psia, the differential pressure on the tank will be 7.35 psi, 1,058 pounds per square foot trying to rip the skins off the spar and ribs.

 

Vent lines must be free flowing both directions.


 

Regards,
Bill Hannahan

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