On Thu, 11 Jun 2020 12:25:58 +0100, nightjar wrote:

Metal cans are best kept full, as that minimises the amount of
condensation that can form inside.

Will enough water vapour get into a nominally "sealed" fuel can
to be
a problem?

I presume Colin was saying it could get into a part-filled can
while it
was open

Exactly. When you pour the contents out, they are replaced by air, which
contains moisture.

But not a lot. Can't say I've ever found any water in any fuel can.
Bottom of the plastic heating oil tank yes, lots but I suspect that's
rain that gets blown in via the unsealed filler or vent caps. I've
fitted a glass bowl filter on the outlet of the tank since to catch
and see any water coming out of the tank. After water in low points
of fuel line froze enough to starve the boiler of oil...

It is standard procedure on light aircraft to drain water from the
bottom of the fuel tanks during the pre-flight inspection.

I suspect that is more down to an abundace of caution. If you you
think you have x litres of fuel you don't want to find, once up in
the air, you have x litres of fuel and y litres of water. Not that
you should be flying that low of fuel in the first place. B-)

--
Cheers
Dave.

The metal can has a long history and has been lauded in song...

"God rest ye, metal jerry can, let nothing you dismay."

--
Cheers
Clive