[PSUBS-MAILIST] Co2 scrubbers

Thu Apr 27 16:17:42 EDT 2017

It is interesting that aluminum and steel are so dangerous but they are the two materials used to make the HP tanks that contain the O2Hank 

    On Thursday, April 27, 2017 2:03 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alec,Thanks', I guess I better make a change.  Grrrr!  So there should be no SS tubing either.  I use a HP plastic lined ss braided hose to go from tank to hull.  I once found a medical cabinet at our local dump in the metal pile and it was full of regulators and switches and all 1\8  brass  lines.  I can probably feed a 1\8 brass  line through the original penetrator with a brass  fitting screwed into the penetrator.  I am going to check my drawer where I keep that stuff.Hank 

    On Thursday, April 27, 2017 1:33 PM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alec,   I wonder if Swagelok carries brass tubing. Brian 

--- 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: Thu, 27 Apr 2017 13:43:16 -0400

Here Hank, I'm going to re-type a couple paragraphs from the Oxygen Hackers Companion...
Best,
Alec
-----------------For metal parts, brass is definitely the metal of choice when it comes to HP O2. It doesn't spark and doesn't (for all practical purposes) burn. Also, being very thermally conductive, brass can add an extra measure of safety by acting as a heat sink, to dampen the effects of adiabatic heating - a recent study has suggested that oversized brass fittings on hoses made of other materials used with HP O2 can significantly lessen the chance of combustion, by soakin gup excess heat. Aluminum and titanium are definitely out - they ignite easily and burn violently in the presence of HP O2. Steel is not a good choice either - it burns, as anyone who has ever used a cutting torch knows. But the big problem with steel is that is sparks so readily, making it a prime potential source of ignition. SS falls somewhere in between. While it doesn't spark or burn nearly as easily as steel, it is not completely immune. The catch is, even good brass fittings are often rated for only 1500-2000 psi, (100-133 bar), and rarely for more than 3000 psi or so (200 bar). For higher pressure systems, then, there really isn't any affordable choice but stainless steel, and just about everyone uses it. It's hard to get a definitive answer on how suitable SS really is for HP O2. 
.. blah, blah..
When it comes to the Oxygen Index, which measures the pressure of oxygen necessary to sustain combustion once the metal has been ignited, brass is light years ahead of everything else, at in excess of 10,000 psi (666 bar). Stainless steel falls in the 500-1000 psi range, with 316 being the worse, mild steel 100-200 psi, aluminum 25 psi - and titanium 1-2 psi! 
.. blah, blah..
The problem is, the soft parts can act as kindling, to ignite the metal parts, and the metal parts, once burning, can create a major conflagration, one that is just about impossible to put out. Selecting metal parts that resist combustion can create a second level of defense against runaway combustion.------------------
On Thu, Apr 27, 2017 at 12:28 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hmmm, you guys have me worried now.  I have a regular steel penetrator for HP O2,  what am I missing.  If you can pipe HP O2 through a ss pipe then why the special bronze?  I see O2 regulators that are chrome, not bronze.  I just clean the heck out of the penetrator and I hook er up.  Gamma just had a steel penetrator for HP  O2 as well.Hank 

    On Thursday, April 27, 2017 10:15 AM, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Brian
I just made it as per the plans.  It fits through a stainless insert welded into the hull.   I hadnt put the threads on in this pic.  Have a look at the drawing, you can see where they will go.  one each end for the valve fittings and a thread on the main body for the nut to hold it in.  probably makes it look longer than it is. I didn't have an issue getting the material.  I just ordered from a standard metal supplier in UK.  
Was quite expensive though.  
On 27 April 2017 at 16:51, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

James,   that seems like a very elongated fitting, why does it need to be so long?  Was it hard to locate the "phosphor bronze"  I have a piece of bronze lying around but I'm have no idea the grade.

Brian

--- personal_submersibles at psubs. org wrote:

From: James Frankland 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: Thu, 27 Apr 2017 10:05:29 +0100

Hi Brian
I only have 1 O2 tank mounted outside.  Pic here of the bronze through
hull.  Kittredge design but I changed the threads to match my valve
fittings.  The valve is phosphor bronze as specified on the plans.
Even though its low pressure O2, I used tungem (whatever that is)
tubing inside for the O2 with is specially for O2 applications.  I
like it to be super safe.

http://www.guernseysubmarine. com/extended_files/Page647.htm

On 27 April 2017 at 06:26, 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> 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.o rg> 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>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.o
> rg>
> 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> 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> 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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