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That would be 1.4 miles per hour. Wonder what a naca vent that gets the air to slow down smoothly from 250 mph down to 1.4 looks like?
I had to drain a tank on a IV to repair a fuel leak. I plugged the
vent while I removed the drain valve from the bottom of the wing, with the hope
that it would slow the flow of fuel down my arm. I only got about a half
gallon from the tank until the flow slowed to a drip. I don't think the
engine driven pump or boost pump could overcome the vacuum caused by a clogged
vent line. So a clogged vent would stop the engine I'm guessing, not cause
it to surge.
I did the calculation one time to determine the air flow that has to come
in the vents to replace the fuel going into the engine. I have 3/8" vent
lines on my ES and that air is moving through that vent line a couple feet
per second if I remember correctly.
Mike Easley
Colorado Springs
In a message dated 5/18/2011 6:42:57 A.M. Mountain Daylight Time,
n5zq@verizon.net writes:
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?
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{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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