Sean,
Thank you so much for that info. Your knowledge is really appreciated!
Thanks,
Scott WatersSent from my U.S. Cellular BlackBerry® smartphone
From: "Sean T. Stevenson" <cast55@telus.net>
Sender: owner-personal_submersibles@psubs.org
Date: Mon, 07 May 2012 11:22:15 -0700 To: <personal_submersibles@psubs.org> ReplyTo: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] O2
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:
Sean,
Thanks, that is very good info. What physical and cheimical
filters do you use with your welding O2 in your life support
system to be sure all hydrocarbons have been filtered out?
Thanks,
Scott Waters
-------- Original Message --------
Subject: Re: [PSUBS-MAILIST] O2
From: "Sean T. Stevenson" < cast55@telus.net>
Date: Sun, May 06, 2012 9:18 am
To: personal_submersibles@psubs.org
Scott, I have been dealing with issues like this with gas
suppliers for years. The purity issue is nonsense. The
medical grade oxygen is filled from the same bulk cryo
storage as the industrial stuff. The difference is that
medical grade is periodically sampled and analyzed for USP
specs compliance, which adds a cost overhead, and on the
medical grade, the filling procedure is slightly different -
vacuum is pulled, O2 is flushed at low pressure, vacuum is
pulled again and then the cylinder is filled. Industrial
cylinders either have one or no vacuum steps before filling.
The idea is to avoid any kind of hydrocarbon contamination,
but such risk is small. I have been using industrial helium
and oxygen (run through my own physical and chemical
filters) for years without issue. If you can do so, it will
probably be cheaper. If not, just explain your situation to
your GP and you can probably get a prescription. Another
option to look for is so-called aviator's oxygen, which is
certified to have minimal moisture content (prevents
freeze-up issues), but may be cheaper than medical.
swaters@waters-ks.com
wrote:
I was at my local welding and gas supply the other
day and they were asking me how my sub was doing and we
got on the conversation about the life support system
and how it works. They told me they could not sell me
medical grade oxygen with out a prescription from a
doctor which I thought was kind of weird. They said I
might be able to use oxygen that you use for welding,
but it is not as pure. Does anyone on psubs have any
ideas on what to do?
Also I had asked a question a while back about the
tubing in the K-350. I have decided to go with stainless
steal, but was still wondering what wall thickness to go
with and how do you connect them (flair fitting,
compression fitting, or something else?)
Thanks,
Scott Waters
|