Re: Ambient-Dry (was:Pressure regulation)

[SFreihof <SFreihof@aol.com>]

Dave;

In a message dated 98-03-15 01:11:26 EST, you ask:
<< Do you have, or do you know a clever way to figure, how much the water
 level inside will rise as that 'glass' submerges? I mean, the air pressure
 is rising to match the outside (water) pressure because the air is getting
 squished into a smaller area and the cabin is being invaded by water from
 underneath. I'm wondering how much extra space you're leaving down there so
 your feet don't start getting wet as you go deeper. Or will it not even
 rise that much, so that it isn't a concern? Or do you keep adding air to
 maintain the same volume while maintaining the same pressure? Or... what? >>

Pressure increases by about 1 atm (14.7 psi) for every 33 feet of depth (salt
water).  A given volume at the surface (1 atm) will be compressed to 1/2
volume at 33 feet (2 atm), 1/3 volume at 66 feet (3 atm), 1/4 volume at 99
feet (4 atm), etcetera.  This relationship between the volume of a gas and
pressure is called Boyle's Law, where P(1)V(1) = P(2)V(2).  Simple scuba
physics. 

So, to maintain cabin volume, you must add air as you descend, and bleed off
air as you ascend.  A simple scuba regulator can do this, but be aware that
flow rates are limited.  Multiple regulators can, of course, alleviate the
flow rate problem, and redundancy is good!  Nonetheless, the maximum dive rate
may be limited by the supply capabilities of the regulators.  The regulator's
second stage must be mounted low in the hull where water pressure is greatest.

You also ask:
<<What sorts of depths and times are those? I'm not asking so I can fake my
way around study or training, scuba certification, etc. -- but so's I'll
know what range that is so I can make sure I'm avoiding it altogether. >> 

Basically, at depths less than 30 feet, you have unlimited time.  At 60 feet
you have an hour, and at 120 feet you have 15 minutes.  The No Decompression
Limits are in any dive manual.  Also of concern are the Dive Tables, and the
Repetitive Dive Tables.  I would STRONGLY recommend you be a certified scuba
diver before you attempt to dive an ambient-dry or wet sub.  

<<I have thought about doing this myself. So, will the whole thing sink like
a stone (or more like a heavy metal thing with holes in the top and bottom)
if both hatches are stupidly opened while submerged? Or are you planning
for so much other flotation stuff that the cabin air isn't what's keeping
you from sinking in the first place? I mean, the way I've thought about it,
you have to make the whole thing heavy enough to submerge the air volume
inside, right? Then add ballast tanks which keep that whole mass floating
when they're full of air, and let it sink when the air is let out. So if
you let the air out of the cabin too, there'd be no way to get it back up.
Right?>>

Yes to all questions, except maybe the last, which depends on design.  If the
ballast tanks are large enough (equal to or greater in volume than the cabin),
then blowing them dry will be enough to float the sub.  In my design, that's
not the case.  An alternative is to blow tanks AND drop weight.  This is
possible if you have (for example) a jettisonable battery pod and ballast
weights.  That's my design.  And, thirdly, you have motor power which
(depending on power) could drive you to the surface.  If all else fails, ditch
the sub and swim home.

In reference to scrubbers, you said:  <<I was also wondering where you get
properly get rid of the stuff once you've used it -- or whether it's something
which can be baked or squeezed or otherwise processed to make it re-usable.>>

As I said, I know very little about scrubbers, but you make a good point.
Does anybody know if the CO-2 absorbants are recyclable?