I am using gases for diving, not for 1 atm life support.
Nevertheless, the concept is the same as a filter stack you would
use with a breathing air compressor, except that it will be exposed
to 100% oxygen and must be designed accordingly. The only other
difference is that instead of filtering from the compressor outlet,
you are filtering from storage cylinders, so water removal and CO2
removal should be non-issues. My filter stack is overkill - it was
one of those hobby projects that I ended up going overboard on
design just because I could. It was originally intended for use
with an oiled compressor. When the compressor purchase fell
through, I made the towers smaller so as not to have a lot of wasted
volume, but finished the filter project nonetheless. Gas grade as
delivered from my gas supplier is a non-issue, as the purity is
effectively increased when run through the filter. Right after the cylinder valves, I use an in-line particulate filter (replaceable sintered filter element) to catch anything physical, such as dirt that might find its way into the valve orifice when the leased cylinders are used elsewhere, from entering my system. I think this is a Swagelok TF series filter. Then to the supply pressure gauge, check valve, pressure regulator, fill pressure gauge, filter stack and needle (flow control) valve to the fill whip (which has the fill line bleeder). Just before the flow control valve are the (now diminutive) filter towers, which pass the gas sequentially through: 1) aluminum oxide / potassium permanganate (Molecular Products Sofnofil) 2) silicon dioxide (silica gel) 3) 13X molecular sieve media: sodium oxide / calcium oxide / aluminum oxide / silicon oxide (Molecular Products SofnoSiv) 4) activated carbon (Molecular Products Chemsorb 1000) 5) platinum/palladium/tin oxide catalyst (Molecular Products Softnocat 423) Since there isn't much in the way of contaminants (not dealing with compressor oil or atmospheric CO2/CO) when you're filling from storage cylinders, the filter replacement schedule is out the window. Rated shelf life of the 13X media is 12 months, so I refresh everything once a year. For a filter dedicated to simply cleaning up bottled gas (which is probably already close to perfect), you're probably fine with just a physical filter, 13X and carbon, but even that is wasted effort for sub life support due to the fact that you're not breathing the gas under pressure, nor directly from the cylinder(s), and that you will be processing your cabin air anyway. It makes more sense to scrub your air at 1 atm, since you don't then have to design for cylinder pressure, and can incorporate hydrocarbon scrubbing media into your CO2 scrubber design to continually remove contaminants that may be introduced downstream of your HP gas supply. Even an off-the-shelf activated carbon impregnated filter incorporated into your scrubber is probably sufficient for this purpose. -Sean On 2012-05-07 06:07, swaters@waters-ks.com wrote:
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