Re: [PSUBS-MAILIST] Life Support Revisited

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Jon:
        No problem. One other thing that is seldom mentioned is the
cabin-pressure guage. This is one of the most referenced pieces of
instrumentation during a dive. Although high or low cabin pressures are not
unsual - within a limited range - once temperatures, etc., have reached
equilibrium, it should should hold relatively steady.
         ( I guess I should further clarify: If you are smoozin; along at a
depth where the ambient temperature is, say, 45 degrees F and you ascend to
a depth where the ambient temperature is, say, 60 dergrees F . . .there
will be an expansion of the cabin gas - 'cuz the cabin temperature will
shift upwards - not as much as the outside shift, but sufficient to cause
an increase in cabin pressure that will only go down as you metabolize the
O2. Conversely, if you've been siting on deck in hot weather, waiting for
permission to dive, the cabin pressure will fall - sometimes dramatically-
when you hit the cold water. You might say say " Yeah, well, the
bellows-add would be adding like crazy and would soon bring the cabin
pressure back to normal" - and it does - but the sealed-bellows gas is also
affected by temperature, just like the cabin, but not as dramatically.
That's why a properly designed O2 system has a bypass lever/button to add
O2 when/if  required.)
        The cabin pressure guage is simply a sensitive altimeter/barometer.
We sell our fancy Nuytco Newtsub cabin pressure guages with color-coded
dial and Newt logo/insignia for mega $, or, you can just buy a good quality
sky-divers altimeter and change the face to whatever units you want ( as we
do! . . .don't forget the lucky newt, tho')and Bob's yer uncle!
Don't leave the surface without one. Just like O2 meters, they are 'cheap
like hell' and should be used. ( Remember, we are talking about cabin
pressure, not O2 percentage/partial pressure)
        As I said, hi or lo pressures are not neccesarily cause for alarm
but you should continously aware of the cabin pressure and WHY it is hi or
lo. If the cabin pressure is lo or hi and you don't know why, then it's
imperative to stop everything else you're doing and figure it out  . . .or
switch to your alternate LS system ( you do have a totally redundant LS
system, right??) or get your ass back to the surface, muy pronto!
        
Phil Nuytten