Positive Tank Pressure

[Greg Esres]

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.

[Ben Jackson]

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/

[Mike Rapoport]

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.
>
>

[Greg Esres]

<<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?

[Greg Esres]

<<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.

[Dave Stadt]

"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.

[Kyle Boatright]

"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.
>
>