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