[PSUBS-MAILIST] Co2 scrubbers

Sat Apr 29 09:16:35 EDT 2017

Cliff, I am curious as to why you are cycling the O2 between the permissible limits, instead of attempting to maintain the environment at 20.9% continuously? The latter control scheme provides some safety margin in that a decrease or rise in O2 level is indicative of a possible problem well before you fall outside of the limits. If you allow a decline to 18% or rise to 23% by design, you're already in alarm if anything goes wrong at either limit. If it is a matter of frequency of valve cycling, perhaps setting control thresholds at something like 19.25 and 21.75 would permit the cyclic control while still allowing some detection and response time before alarming?

Sean

On April 27, 2017 8:46:52 PM MDT, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Brian, the diagram below shows the arrangement I have for life support.
> I
>bring HP (2000 psi) O2 into the Air Management Oxygen Control (AMOC)
>unit.
>The AMOC unit has a pressure reducing regulator that drops the pressure
>to
>about 10 psig.  The O2 this passes into a O2 mass meter/controller when
>in
>Automatic mode or through an adjustable needle valve in manual mode. 
>There
>a manual O2 variable area, float meter to see O2 rate in SLM.  A PLC
>talks
>to the AMOC unit to control O2 supplied into the cabin.  Also in the
>AMOC
>box are all the life support sensors, CO2 concentration, O2
>concentration,
>Relative Humidity, O2 tank pressure, O2 makeup rate, Cabin temperature
>and
>Cabin pressure.  When O2 concentration drops below 18%, PLC tells the
>controller to open and deliver O2 at a rate of 4 SLM.  When the O2
>concentration reaches 23% the PLC turns off the controller.  This cycle
>is
>repeat every 30 - 60 minutes depending on the pilot.
>
>Cliff
>
>[image: Inline image 1]
>
>[image: Inline image 2]
>
>On Thu, Apr 27, 2017 at 9:25 PM, Brian Cox via Personal_Submersibles <
>personal_submersibles at psubs.org> wrote:
>
>> Cliff,   Do you reduce your incoming O2 with a regulator off the O2
>> bottle?  Then come in with lower pressure into the cabin?
>>
>> Brian
>>
>> --- personal_submersibles at psubs.org wrote:
>>
>> From: Cliff Redus 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 17:36:51 -0500
>>
>> Alec if you keep reading down just below the section you site in the
>> "Oxygen Hackers Companion", you will  note that the author says
>"Stainless
>> steels are used extensively in HP O2 systems ..."  "CGA specifies
>that
>> valves for O2 tanks should be make of either brass or SS. NASA has
>> researched this issue (SS for O2 service) and does not reject SS
>> exclusively.
>>
>> I use O2 clean SS 1/4" tubing and Swagelok SS valve and fittings for
>all
>> my O2 service on my boat .  If you O2 clean the systems and use
>approved O2
>> lubricants and O-rings, then you, in my mind, have removed the "fuel"
>leg
>> of the "Combustion Triangle(fuel, oxidizer and ignition source).  If
>you
>> are then careful to mitigate adiabatic compression by slow transfer
>rates
>> of less than 60 psi/min, then in my mind you have reduced the risk
>> associated with adiabatic heating in HP O2 to an acceptable level.
>>
>> I for one am not going to rip out all my SS O2 tubing and valves and
>> replace them with brass.  In my mind there is certain level of risk
>> associated with this psubs, O2 fires in O2 clean SS tubing is like
>risk
>> level 97 out of 100!  Given the rough handling O2 lines and tanks can
>get,
>> I would be more afraid of O2 leakage caused by the use of soft tubing
>and
>> fittings than the combustion issues sited above.
>>
>> I went back an looked at the pictures I took from the 2009 Vancouver
>Psub
>> convention in Phil's shop. All tubing and valves I could see where
>SS.
>>
>> Cliff
>>
>> On Thu, Apr 27, 2017 at 12:43 PM, Alec Smyth via
>Personal_Submersibles <
>> personal_submersibles at psubs.org> wrote:
>>
>> 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
><personal_submersibles at psubs.org>
>> wrote:
>>
>> From: James Frankland via Personal_Submersibles
><personal_submersibles at psubs.
>> org <personal_submersibles at psubs.org>>
>> To: Personal Submersibles General Discussion
><personal_submersibles at psubs.
>> org <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
>> <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 <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
><personal_submersibles at psubs.org>
>> wrote:
>> >
>> > From: Alec Smyth via Personal_Submersibles
><personal_submersibles at psubs.
>> org <personal_submersibles at psubs.org>>
>> > To: Personal Submersibles General Discussion
>> > <personal_submersibles at psubs. org
><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
><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
><personal_submersibles at psubs.org>
>> wrote:
>> >
>> > From: Alec Smyth via Personal_Submersibles
><personal_submersibles at psubs.
>> org <personal_submersibles at psubs.org>>
>> > To: Personal Submersibles General Discussion
>> > <personal_submersibles at psubs. org
><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
><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
><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
><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
><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).
>> >
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