Re: PVC, PLASTIC COKE BOTTELS & RUBBER SUBS???

[shawl@torchlake.com (Jonathan Shawl)]

Hi Jon Hylands
There is no difference between water pushing in on the outside and a vacuum pulling
in on the inside.
Pressure difference is pressure difference.
If you have 0 on the inside and +15 on the outside that is 15 difference.
If you have +15 on the inside and +30 on the outside it is still 15, and the load on
the hull is the same . Water and air makes no difference to the hull either,
pressure is pressure. When I hooked up the vacuum pump to the hull and tested it to
implosion at 15" Vac. that was exactly the same kind of stress as dropping it down
about 15' in the water.
Jon please reread that last e-mail you are referring to. The material I was using
had nothing to do with vacuum, it was a aircraft wing fuel tank. It was designed to
carry fuel at a slight internal positive pressure. Then I tried to make a sub out of
it and, BANG. Now if it had good ribs in it, I could have made it go deeper but, how
deep...???? I can't calculate it because it is so thin and it's aluminum and it is a
cone shape etc. That is why I will always stick to steel from now on, it's a time
proven and predictable material.
Jon Shawl

Jon Hylands wrote:

> On Fri, 02 Jul 1999 11:40:20 -0400, you wrote:
>
> >  A little later at
> > around 15" Vac I was tapping on it some more and BANG it flattened faster than
> > "lightning", and it did get a lot wider the other way.
>
> I think there's a major difference here. You're talking about making a
> vacuum inside, with one atmosphere of pressure outside, which the
> material is designed to work with.
>
> I suspect the failure mode would be significantly different if that
> item was underwater, since the water outside is pushing on the
> outside, rather than just trying to suck the air out like a vacuum
> does.
>
> Later,
> Jon