[PSUBS-MAILIST] Co2 scrubbers
Sean T. Stevenson via Personal_Submersibles
personal_submersibles at psubs.org
Sat Apr 29 15:54:32 EDT 2017
Cliff, I'm not sure how PID loops are implemented on your PLC. My experience is predominately with PACs which are a little more versatile, albeit more expensive. In any case, you don't necessarily have to filter your process variable if it is noisy, as long as the center of the noise band is properly representative of the measurement. Another alternative is to apply rate limiting to the PID output. What loop rate does your PID calculate at? For O2 addition, you probably don't need a strongly responsive system. If the existing control is meeting expectations, I wouldn't mess with it. I was just worried that you had no margin for error.
Sean
On April 29, 2017 11:24:42 AM MDT, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean, I misspoke, I went back and looked at my PLC ladder logic and it
>turns out that I turn on the O2 when the concentration drops below 20%
>and
>turn off the controller when it goes above 22%. So the control is
>between
>20-22 not 18-23. Attached is a graph showing the O2 concentration in
>automatic O2 makeup mode. You can see that the average O2 in the boat
>when
>in Automatic O2 makeup mode is about 21%.
>
>[image: Inline image 1]
>
>
>You do make a good point about an alternative strategegy which is to
>use a
>PID controller with the set point set being 20.9%. I have many spare
>PID
>controller loops avaiblle in the PLC cpu so it would be an easy change
>in
>implement. Part of the hesidancy to change was that the sytem as
>designed
>is working fine. Also it kind of comforting to hear and see the O2
>turn
>on during the makeup cycle. Part of me says '*if it ain't broke don't
>fix
>it*', and another part of me likes to tinker. I have some noise around
>the
>O2 sensor reading. To implement this signal as part of a PID control
>loop
>I would need to do some filtering of the O2 concentration measurement
>to
>remove some the noise. In the initial setup of the AMOC unit, I had a
>O2
>solenoid valve where the comptroller now sits. I replaced the O2
>makeup
>solenoid mainly because I wanted to measure the O2 rate and was able to
>fine a very nice O2 controller / rate sensor on ebay for next to
>nothing.
>So right now I am just sending the controller a high and low signal to
>make
>it duplicate a solenoid valve on and off but it would work just as well
>and
>maybe better in a PID control loop as the control variable. After I
>get
>back from the Islamorada trip, I may set up a test of using PID control
>of
>O2 makeup just to see how it compares. With the system as now
>designed.
>
>Thanks for the thoughts.
>
>On Sat, Apr 29, 2017 at 8:16 AM, Sean T. Stevenson via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>> 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 m!
>>> inutes
>>> 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", y!
>>>> ou 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>>
>>>> Subje!
>>>> ct: 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 Submersib!
>>>>> les
>>>>> 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
>>>>>
>>>> th!
>>>> ere
>>>>
>>>>> anyone else out there that is using a first stage reg on a HP
>exterio
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