[PSUBS-MAILIST] Co2 scrubbers

Alec Smyth via Personal_Submersibles personal_submersibles at psubs.org
Tue Apr 25 22:25:36 EDT 2017 

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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