Further to my posting of yesterday on this same subject, I have looked at the
Andair website (www.andair.co.uk). Andair makes two check valves. One of
conventional design and a similar one with a pair of small holes drilled
through the internal shuttle. The latter is the one intended for use in fuel
tank vent lines. The stated purpose of the two holes is to prevent
overpressurization of the fuel tank due to thermal expansion of the fuel
while the plane is parked. They don't make any mention of the problem that I
alluded to in my posting, namely, the need to vent the tank during climb and
I question whether or not "two small holes" are adequate to do the job.
Assuming these two small holes are adequate to prevent thermal
overpressurization, I have to wonder if the check valve actually does any
good. In other words, does it pass a similar amount of fuel as would be
passed if the check valve weren't there, just more slowly? Wouldn't you be
better off without the check valve and avoid all the failure modes associated
with either pluggage of the two holes or failure of the check valve to open?

At the conclusion of my previous posting, I included a PS suggesting that a
float valve might make more sense than a check valve. In doing so, I hadn't
considered the thermal expansion issue. On that basis I retract that
suggestion. More than ever, I think I will fly naked (i.e., nothing in the
vent line) and just make a point of flying coordinated and parking on the
level.

Jim McKibbin