[PSUBS-MAILIST] Co2 scrubbers

Thu Apr 27 13:25:45 EDT 2017

Hi Brian,

The sequence is correct but I would use brass tubing, valves, and fittings
due to the high pressure. Ever seen a welding O2 tank with the valve made
of anything but brass? I'm not sure what James' "tungem" is, I've never
even heard of that. But anyway... as a starting point I would recommend
getting a copy of the Oxygen Hacker's Companion. It is truly indispensable
reading. The problem with O2 is that you can have a very bad day due to
causes that are easy to overlook, or which might be perfectly OK with HP
air.

Best,

Alec

On Thu, Apr 27, 2017 at 1:26 AM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Alec,   So on that bronze fitting, if I was using HP  O2 coming into the
> cabin I would go from the O2 tank outside with SS tubing , then go to a
> bronze thru hull fitting ?  Then a shut off valve on the inside ( a needle
> valve type) and then to my flow meter.
>
> Brian C
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.
> org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] Co2 scrubbers
> Date: Wed, 26 Apr 2017 21:08:08 -0400
>
> I understand Kittredge used bronze, which is good because it's a material
> that is very unlikely to initiate an O2 fire. However, in my case we're
> already dealing with low pressure at that point, so SS should be fine.
>
> Best,
>
> Alec
>
> On Wed, Apr 26, 2017 at 10:22 AM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Alec,         When you transition your O2 thru the hull don't you have to
> have a bronze fitting as a thru hull fitting?
>
> Brian C
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.
> org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] Co2 scrubbers
> Date: Tue, 25 Apr 2017 22:25:36 -0400
>
> Yep, I did that on both Snoopy and Shackleton. On Snoopy there is one O2
> tank outside, which leads to a 1st stage. From there through the hull and
> on the inside a pediatric flow regulator. Shackleton has the same thing,
> except two of everything. Same exact setup as Snoopy except one port and
> one starboard, for redundancy. Good news, I have run both of them several
> times already and they did not turn into flamethrowers. But I'm quite
> particular about the cleaning. For instance I got a pair of little O2
> pressure gauges but decided not to install them because they didn't arrive
> bagged. I did my own cleaning (twice) on the LP components per Oxygen
> Hackers Companion instructions. The HP side (really just a regulator and a
> 1st stage) were purchased O2 clean.
>
>
> Thanks,
>
> Alec
>
> On Tue, Apr 25, 2017 at 10:03 PM, Rick Patton via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Hank,
>
> Yeah I think your situation would be different than what I would be
> experiencing. I personally just don't believe that there should be any HP
> plumbing inside a one atmosphere vessel but that's just my opinion. Is
> there anyone else out there that is using a first stage reg on a HP
> exterior tank, 02 or air?
>
> Rick
>
> On Tue, Apr 25, 2017 at 1:48 PM, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Rick,
> I know this may not apply, but, Elementary 3000 has  external O2 with a HP
> line to the hull penetrator and inside the hull there is a tower valve with
> medical O2 regulator  mounted directly  to that penetrator.  There is no
> internal HP O2 line.  I am not sure why you want to reduce the O2 pressure
> before the hull.  Gamma also had the identical system for auxiliary O2 when
> I first got it.
> Hank
>
>
> On Tuesday, April 25, 2017 5:38 PM, Rick Patton via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>
> I sent out an email regarding balance verses unbalanced 1st stage regs for
> an 02 tank that would be on the outside of a sub but didn't get a response
> so not sure it went so decided to attach to Alan's last email to see.
> Would love to hear from those who have their HP tanks on the outside of
> there sub and knock down the HP to LP at the tank valve to keep HP from
> entering the sub and weather you have an unbalanced or balanced 1at stage.
>
> Thanks
>
> Rick
>
> On Sun, Apr 23, 2017 at 3:29 PM, Alan via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Cliff,
> forget the rumours of sheep everywhere in N.Z..
> We have a very sophisticated coffee culture down here! Translating that
> knowledge over to scrubbers will make for a safer unit.
> Am enjoying this thread as I need to make up a scrubber at some time.
> Am going with 2 scrubbers. Once I know my hull size more accurately I'll
> be contacting Molecular Products tech help, as they have a computer to
> calculate flow rate needed to keep you within your required limits.
> Cheers Alan
>
> Sent from my iPad
>
> On 24/04/2017, at 1:11 PM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.
> org <personal_submersibles at psubs.org>> wrote:
>
> Yes I like it,  Psub Baristas with one small difference, if you get your
> DIY coffee machine wrong, you get a bad cup of Joe; if you get your DIY CO2
> scrubber wrong you die!
>
> Cliff
>
> On Sun, Apr 23, 2017 at 5:37 PM, Alan via Personal_Submersibles <personal_submersibles at psubs.
> org <personal_submersibles at psubs.org>> wrote:
>
> Some great thoughts thanks.
> This all seems very much like the art of coffee making!
> You have the type of bean ( absorbent choice). There is the grind (
> granule size)
> Moisture has an effect on coffee extraction.  There is the amount of
> coffee grind
> in the shot! If you have differing volumes of absorbant in the scrubber
> this would
> have an effect. There is the tamping of the grind that effects the speed
> water flows through the ground coffee, which is equivalent to how the
> absorbent is compacted. There is a set perfect time that it should take for
> the water to flow through the grind
> to get the maximum desired extraction, this relates to the previous
> factors & the pressure of the pump. With a scrubber the pump is replaced by
> the fan & the flow
> rate is what is required to keep CO2 levels below required levels & this
> is dictated
> by the size of the hull & number of passengers.
> Baristas can spend ages fine tuning their coffee machines every day &
> during
> the day.
> Not saying we should be this fussy; but there are a lot of factors to
> balance if
> you want it perfect!
> Alan
>
>
>
>
> Sent from my iPad
>
> On 24/04/2017, at 9:33 AM, james cottrell via Personal_Submersibles <personal_submersibles at psubs.o
> rg <personal_submersibles at psubs.org>> wrote:
>
> Hi Cliff,
> Thanks for the excellent info. Great research. If I could add a couple of
> things they would be-
>
> Pushing air through absorbent vs pulling air has different effects too.
> Pushing air through with a blower has the benefit of slightly higher
> pressure in the media which can yield more efficiency compared to drawing
> air through which lowers pressure.
> However, too much airflow can cause the the media to dry out and lose
> effectiveness. Humidity may have to be controlled within limits.
> Pushing air through can also cause uneven distribution and poor
> performance depending on scrubber design.
>
> So the challenges are to keep humidity within limits, air flow sufficient
> with even distribution all without exceeding available power over duration
> of dive (especially in an emergency).
>
> For these reasons, lung powered devices are great as a back up. The lungs
> provide the airflow and the humidity. If the unit is made from clear
> acrylic, it is possible to use color changing media.
> One last thought- Absorbent cartridges (like micro-pore re-breather
> cartridges) can make it easier to change used up media in the sub during an
> emergency than trying to empty and replace granules. Just pull out the old
> cartridge, insert the new one and continue breathing.
>
> Greg C
> ------------------------------
> *From:* Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.o
> rg <personal_submersibles at psubs.org>>
> *To:* Personal Submersibles General Discussion <personal_submersibles at psubs.o
> rg <personal_submersibles at psubs.org>>
> *Sent:* Sunday, April 23, 2017 1:17 PM
> *Subject:* Re: [PSUBS-MAILIST] Co2 scrubbers on eBay
>
> To elaborate a bit on Alec's comments, a few years back I did some work
> the scrubber for my one-man boat and came away with some conclusions.  The
> first was that a radial design was better than an axial design for air flow
> throws the absorbent and the second was that the goldilocks rule applies
> for fan/blower associated with the scrubber.  Engineers make a
> distinction on equipment used to compress air.  They define a parameter
> known as the specific ratio which is defined as the discharge pressure
> divided by the supply pressure where each pressure is in terms of absolute
> pressure rather than gage pressure.  If the device has a specific ratio
> less than 1.1, they call it fan, if it has a specific ratio greater than
> 1.2 they call it compressor and if it has a specific ration between 1.11
> and 1.2, it is a blower.  What I found from my testing on the scrubber
> was that fans like you would typically see on PC are axial flow and these
> are designed for high flow rates but low head. When you try and use them to
> push air through the CO2 absorbent, they just don't have enough head and
> the resulting flowrate is very low.  In this case they are not operating
> anywhere near their best efficiency point (BEP).  What I found worked
> better were squirrel cage blowers. These are designed for lower flow rates
> than PC axial fans but with more head.  I am sure there are many models
> of squirrel blade blowers that would work but the model I use is from
> Papst, model RL90-18/24.  This blower operates off 24VDC and has a power
> rating of 7.5 W which translates to 0.31 amps.  If you look on ebay,
> these blowers come up all the time.  Back to the goldilocks rule;  to
> meet ABS rules, you have to demonstrate that your life support system will
> operate through the the emergency time period which is 72 hours on the
> backup battery.  The current during this period is known as the “Hotel
> Load” for obvious reasons.  When I tested axial PC fans, they were great
> on battery endurance because they pull a very low current but they did not
> work well because they did not have enough head to overcome the pressure
> drop through the CO2 absorbent material , SodaSorb HP in my case.   This
> showed up as having erratic CO2 levels in the boat and not being able to
> sustain concentrations less than ABS required maximum of 5000 ppm (1/2%).
> When I tried larger axial fans like you would use for a bilge fan, the
> unit would keep the CO2 level below the 5000 ppm limit but they pulled way
> much current and  would not last anywhere near the 80 hours.  The Papst,
> model RL90-18/24 squirrel cage blower turned out to be  perfect with
> enough head to circulated  the cabin air  to keep the CO2 level typically
> below 2000 ppm but also because they only pull 0.31 amps.  This blower
> did not let me meet the 72 ABS endurance limit but got me close.  Below
> is a graph of hotel load current through my backup battery and the voltage
> across the backup battery as a function of time on a life support test in
> my boat.  You can see from the graph at about 69 hours into the test the
> backup battery was exhausted.  Also the hotel load started at about 1.6
> amps but slowly climbed to 1.7 amps over the 69 hours.  This hotel load
> was a little higher than the 1.5 amps that I had designed around.  I need
> to go back and look at the contributors to this hotel load and see if I can
> reduce.  I am happy with the 69 hours because during a real emergency
> like be stranded on the bottom due to entanglement, I could utilize at
> least some of the main battery.  For reference, the backup battery
> consist of two AGM  100 Ah battery.  If you divide the capacity by the
> hotel load you get the expected endurance of 100Ahr/1.65A is 61 hours so my
> 69 hours did better than expected.
> .
>
> <image.png>
>
>
> Cliff
>
>
>
>
>
> On Sat, Apr 22, 2017 at 6:07 PM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.o
> rg <personal_submersibles at psubs.org>> wrote:
>
> Hi Brian,
>
> If by "straight flow fan" you mean the geometry you would see on a
> computer cooling fan for instance, they are way less efficient for this
> purpose. I believe the reason is they move good volumes of air but develop
> very little pressure. I've tested both kinds, and the sort I'm using now
> has much better performance. Cliff has done similar tests and had the same
> results.
>
> Best,
>
> Alec
>
> On Sat, Apr 22, 2017 at 6:08 PM, Brian Hughes via Personal_Submersibles <personal_submersibles at psubs.
> org <personal_submersibles at psubs.org>> wrote:
>
> Alec,
> Just ordered a tank holder that has two bungies about an inch apart, used
> to strap tanks down on a boat. I'm thinking I can hang this scrubber from
> the roof using the aft most reinforcing ring, holding it up in the middle.
> If it works, straight flow fan.
>
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