Re: [PSUBS-MAILIST] Re: Your sealed wetsub idea...

[Michael Edwards <me@sustainkauai.org>]

Greetings Dewey:

At this point, my thought was to use a closed curcuit rebreather,
to address some of the problems you are pointing out.

Thanks for looking at this.

Michael

Dewey Mason wrote:

> Hi Guys,
> I have a few thoughts on this whole pressure in a wet
> vs a dry sub thread. While water does not compress,
> the sub will not be TOTALLY filled with water. Even if
> it were, the pressure is a factor of gravity and the
> weight of the water above any given point. That
> pressure does not change due to the hull as a barrier
> unless it is TOTALLY inflexible. NO hull known is
> completely inflexible. If the hull is supported by
> water, the pressure inside and outside will remain the
> same, according to depth. If there is an air space,
> like your lungs or mask, then the hull is not totally
> supported, and the pressure is going to be applied to
> the hull. If it flexes inward, your internal pressure
> goes up. This occurs in a dry 1 atm sub, but the
> compressibility of air means a very slight pressure
> increase. In a vessel filled almost entirely with
> water, even a very slight decrease in internal volume
> would equal a large increase in pressure. It would be
> the same as a wet chamber with a tiny air space. As
> the small volume of gas is subjected to compression,
> the pressure skyrockets. There were several divers
> killed in some of the early chamber trials folks did
> in the mid-1800's by this effect. They tried to breath
> compressed air inside a fully flooded sealed chamber,
> and were immediately subjected to extreme pressure, as
> the gas had no where to go. The pressure vessel will
> expand outward a bit while the pressure increases
> fast. Remember, a chamber rated to a pressure of only
> 100 PSI would be equivalent to some 225 fsw. Most
> regulators will deliver about 120psi-140psi ABOVE
> ambient until there is not enough pressure difference
> between the air source and ambient. An aluminum 80
> holds 3000psi. Before that reaches an equilibrium with
> the inside of your sub, at around 1500psi, the hull
> would probably burst. If not, you would be subjected
> to ever increasing pressure, until you stop
> breathing(BAD). Same would apply to a wet sub where
> you breathed air from a HP source. Unless you have a
> means to remove the spent air, you will die at the
> surface within minutes of sealing your hull. Assuming
> you could even get it to close while you where
> breathing. In which case the pressure at depth
> question would be a bit moot, yes? By the way, I have
> never seen the question of internal pressure increase
> in a DRY 1 atm sub addressed either. When gas is
> added, the pressure WILL go up, unless an equal volume
> of gas is removed. A compressor intaking from the
> inside and venting out would do well here. The physics
> here may be a bit hard to fathom, but the results of
> other's experiments are EXTREMELY obvious and the
> result would be some degree of BAD. A little bad and
> it would not work. A lot bad, and BAD reads FATAL.
> Anyway, just a few thoughts on it, even if it is a bit
> long.
> Dewey
>
> __________________________________
> Do you Yahoo!?
> New Yahoo! Photos - easier uploading and sharing.
> http://photos.yahoo.com/