[PSUBS-MAILIST] Co2 scrubbers

Wed Apr 26 15:12:40 EDT 2017

Thanks for the picture James,
Are you carrying more than one tank for your 02?

Rick

On Tue, Apr 25, 2017 at 11:14 PM, James Frankland via Personal_Submersibles
<personal_submersibles at psubs.org> wrote:

> Hi Rick,
> I have 02 system as you describe.  I'll find a picture.  Ive got a 02
> clean scuba 1st stage (not sure if its balanced or not, or even if it
> matters in this situation as im not breathing off it) with relief valve set
> to 14 bar.  Through hull, stop valve, internal flow regulator.  Very simple
> system.  Just the hose is not shown in the picture.  I also later changed
> the flowmeter to one that had smaller increments as that one the minimum
> was 1/2lpm which was way too much.
>
> http://www.guernseysubmarine.com/Extended_files/Page26979.htm
>
> regards
> James
>
> On 26 April 2017 at 00:38, 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> 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> 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.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.org>
>>>> *To:* Personal Submersibles General Discussion <
>>>> 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.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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>>>>
>>>>
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