Positive Tank Pressure

Anyone have any information about how important it is for a fuel tank
to maintain positive pressure on the inside? I mean *above*
atmospheric.

Part 23 only makes reference to tanks with bladders; these are
required to maintain a positive pressure so they won't collapse.

A C172, though, doesn't have bladders. The forward facing fuel vent
most likely *does* provide positive tank pressure, but that may not
actually be necessary in order to ensure fuel flow.

In article ,
Greg Esres wrote:
Anyone have any information about how important it is for a fuel tank
to maintain positive pressure on the inside? I mean *above*
atmospheric.

http://www.delta.edu/slime/cancrush.html

--
Ben Jackson

http://www.ben.com/

Clearly it isn't required or the plane couldn't be started while stationary
on the ground.

Mike
MU-2

"Greg Esres" wrote in message
...
Anyone have any information about how important it is for a fuel tank
to maintain positive pressure on the inside? I mean *above*
atmospheric.

Part 23 only makes reference to tanks with bladders; these are
required to maintain a positive pressure so they won't collapse.

A C172, though, doesn't have bladders. The forward facing fuel vent
most likely *does* provide positive tank pressure, but that may not
actually be necessary in order to ensure fuel flow.

Check out Parts 23.965 and 23.975.

I see nothing of relevance in these two sections. .965 talks about
the pressure that a tank must be able to withstand and .975 talks
about venting...nothing about positive pressure. What am I missing?

http://www.delta.edu/slime/cancrush.html

All I see on that page is the perils of negative pressure. Of that,
I'm well aware. Doesn't seem relevant to the issue of maintaining
positive pressure.

"Greg Esres" wrote in message
...
Check out Parts 23.965 and 23.975.

I see nothing of relevance in these two sections. .965 talks about
the pressure that a tank must be able to withstand and .975 talks
about venting...nothing about positive pressure. What am I missing?

The tanks in my plane are not under positive pressure. Haven't been since
March of 1947. I see no reason that they need to be. Gravity hasn't failed
yet.

"Greg Esres" wrote in message
...
Anyone have any information about how important it is for a fuel tank
to maintain positive pressure on the inside? I mean *above*
atmospheric.

It isn't important. All you want to do is provide a vent so the tank doesn't
go negative.

Part 23 only makes reference to tanks with bladders; these are
required to maintain a positive pressure so they won't collapse.

A C172, though, doesn't have bladders. The forward facing fuel vent
most likely *does* provide positive tank pressure, but that may not
actually be necessary in order to ensure fuel flow.