Hi, Daniel:
Sunday, again - a little time to wander thru' the debbil box! If
you need ultra lo-cost LSS, put in an oxygen tank with a medical regulator
that has a needle valve/ flowmeter on it - these are nickles and dimes on
eBay - less than a 100 bucks will get you a 40 cu ft tank and reg - if you
want 72 hours, get two. Get an O2 analyzer/monitor ( another 50 -100 bucks
in eBay 'scuba') - buy a 10 dollar wind - up oven timer and set for 5
minutes to remind you to check 02 level (buzz! /rewind) and adjust flow (
once you get it dialed in, you may only touch it a couple of times during
a
6-8 hour dive) For scrubbers, get a low voltage hair dryer and snip the
heating coil out of it - or a 12 volt automotive heater blower, etc, and
attach to the end of a piece of 6 inch PVC pipe- or clear acrylic if you
are using color indicating absorbent.Screen both ends ( 2 layers of
plastic
bug screen mismatched so holes dont line up!) Stuff it full of Sodasorb,
Sofnolime or soda lime of choice, and there y'go ! For a passive
scrubber,
get some 400 foot, 16mm movie reels, make plastic snap-on plastic bug
screen covers - they're good for a couple of hours each, and the center
sprocket hole makes a convenient mounting point.
For a virtually no-cost LSS, install a large diameter vent valve (
light cracking pressure non-return valve) and instead of coming to the
surface every two hours, double your cabin pressure from your air ballast
supply tank or from an interior scuba bottle after the intitial 2 hours
bottom time ( if you're happy with the '2 hours before surfacing to
replace
cabin air' scenario) - this will halve the PP C02 and still provide
sufficent 02. After another 2 hours at 33 feet cabin pressure, you can
increase it to 66 feet to gain additional time, but must be mindful of
the
air no-decompression limits. The excess cabin pressure will vent on ascent
- or rig your hatch with a couple of bungee cords so it will burp on a
couple of pounds excess pressure - if you're concerned about the vent
valve
sizing or your ability to make a relatively controlled surfacing.
Obligatory disclaimer: Please note that I don't recommend either of
these approaches, only offer this info as examples of what has been done
in
the past. FYI, the 02 tank/liter flow reg/oven timer/ manual adjustment
was
the way most commercial deep-diving subs provided LS in the 50's and 60's
and even into the 70's. The pressure-down system was used a lot during
early (60's)bounce bell one-at observation dives when a lock-out wasn't
contemplated, only a look-see at problem - and the bounce bells weren't
fitted with scrubbers.
Phil Nuytten
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