RE: [PSUBS-MAILIST] co2 monitor source

["Alec Smyth" <Asmyth@changepoint.com>]

please see below...

-----Original Message-----
From: Cliff Redus [mailto:dr_redus@devtex.net]
Sent: Friday, November 08, 2002 3:38 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] co2 monitor source


Alec, with all of the components for your CO2 scrubbing system in place,
have you had a change to measure the flowrate of the air and thus the time
to circulate your entire cabin volume through the scrubber?

AS: No, I haven't measured that because I'm basing the calculation just on the amount of absorbent to be carried, per Phil's paper. I also picked the fpm of the fans according to the values mentioned in that paper, although obviously that's pretty flawed reasoning since the resistance of any two scrubbers to airflow is going to be quite different.


You did not mention any control aspects so I am assuming that you will run
the scrubber continually and check CO2 and O2 with monitors. Which way did
you decide to go on O2 makeup, fixed flowrate set by needle valve or Nuytten
type demand valve?

AS: I'm planning to run it continuously because its quiet and has very low current draw. When this drops cabin pressure, O2 will be injected. I've been leaning towards the mechanical approach, but am currently working on other systems and have not tried to source the parts for that. If I have trouble doing so, and I see one of you guys has something simple that's electronic, I'm open to copying ideas!

Are you planning on adding any absorbents sections in your first can for
water to control humidity or are you just going to bring a towel?

AS: This was one of the big questions I had... how much water would it produce? What I found is it gets very damp indeed inside the cans, yet they hardly drip at all. What does worry me is the effect of all that humidity on the fans. At any rate they kept going through my tests, and the reason I've got two fans in series as opposed to parallel is to ensure some continued flow in case one fails. If they both fail, of course, there's always lung power.


Cliff


----- Original Message -----
From: "Alec Smyth" <Asmyth@changepoint.com>
To: <personal_submersibles@psubs.org>
Sent: Friday, November 08, 2002 2:07 PM
Subject: RE: [PSUBS-MAILIST] co2 monitor source


> Actually I just finished my scrubber a few weeks ago. I have tested it in
my garage and it appears to work well, but I would certainly not recommend
it as something "guaranteed", as I have not yet had the opportunity to test
it inside an airtight cabin. For that, I'll have to have the O2 part of the
equation built too. But in case anyone wants to leverage some ideas for
their own design, here goes:
>
>
> Objectives:
>
> My sub is going to be a very uncomfortable one, because the pilot's
position is prone and its a tight fit. So my outings are unlikely to be more
than an hour or two long. Therefore I am following a strategy similar to
Cliff's, and making a small capacity scrubber but carrying spare Sofnolime.
No point throwing out a ton of Sofnolime that's barely used, but I did want
a stock on hand in the sub for use in emergencies.
>
> Also, I want to minimize noise. I can't imagine anything less appealing
than lying in a small steel tube with a vacuum cleaner motor going for
several hours.
>
>
>
> Design:
>
> Scubbers are normally either blowers or suckers. What I did was a
combination of both. The fans suck air in through a canister, but they blow
it out through a second canister. This means the fans are isolated between
two layers of Sofnolime, or in other words muffled. Of course, the second
canister is scrubbing air that is already scrubbed. For this reason, the
second canister needs to be smaller than the first. With a ratio of 1 to 3,
I find the chemical turns purple at approximately the same time in both
cans, which is what you want for efficiency. You can barely hear this
scrubber in operation, it makes less noise than the battery charger I was
using as a power source in the tests.
>
>
>
> Construction and parts:
>
> The first can is an industrial LAMP I purchased from MSC. Its a special
lamp for use in wet environments, such as inside a car wash. This means its
airtight, sealed with o-rings. The lamp is a clear plastic cylinder which
screws into a base. I drilled the bottom of the cylinder with hundreds of
very small holes, using a 0.01" drill, effectively turning the bottom into a
sieve. In the mouth of the can, I placed a sort of stopper with a wery fine
stainless mesh, which is spring loaded (I still need to get or make the
spring). This is to keep the Sofnolime tight, to prevent air tunnels
developing in it. The mouth of the can is also just the right size to accept
an activated carbon cartridge of the sort found in respirators, which I
intended putting in there for filtering out smells. However, I don't think
I'll be using the carbon cartridge because it creates so much resistance to
airflow. But anyway, that's an idea you might want to pursue if you use
stronger fans.
>
> The lamp screws into a plastic block I machined, which contains two
computer cooling fans from Radio Shack. I ran the thing continuously for a
week as a burn in-test, and they held up. The fans are rated for 20,000
hours. I also ran it in a tub with dry ice in it, so it was essentially a
100% CO2 concentration. You should see the temperatures the chemical
reaches... its a good test.
>
> The second can is made of PVC plumbing components and very fine stainless
mesh. I made it so the scrubbed air exits horizontally. So the intake is
vertical and near the bottom of the sub, while the exit is horizontal and
higher up. This should prevent me from scrubbing just-scrubbed air. I am not
counting the second can in my calculations, its just a sound muffler which
happens to add a little scubbing power as a bonus. So I'm not troubled by
the second can not being clear, as I'll only be monitoring the main one.
>
> I'll get a picture and put it on the site for you all to see, in case this
is clear as mud. This is not an off the shelf solution, but at lease nearly
all of it is off the shelf parts from a hardware store.
>
>
> cheers,
>
> Alec
>
>
>
> -----Original Message-----
> From: Cliff Redus [mailto:dr_redus@devtex.net]
> Sent: Friday, November 08, 2002 12:27 PM
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] co2 monitor source
>
>
> Alan
>
> > I like the Nuytten method, too. I'm planning to revamp
> > my O2/CO2 system this year. Any thoughts on a good,
> > compact scrubber for my tiny, single-place Explorer?
>
> I have seen some face mask type units that have the cartridge in the mask
> but I don't know of any non face mask complete units.  What I have chosen
to
> do is use a transparent cartridge holder from Aqua-Pure (AP12T) and make
my
> own cartridges.  The clear lexan bowl lets you monitor the color change in
> the absorbent.  And the size allows me to have my normal mission duration
(7
> hours) in one cartridge.  I then store the remaining cartridges to give me
> 72 hours of emergency time. I am using a  marine compact PVC inline blower
> from Jabsco (12 VDC, 3" In-line, model 3048900000) to circulate air
through
> cartridge holder and cartridge. My intake point is the lowest part of my
> boat at the stern and my exhaust point is directed blow across my bow
> viewport (Busby indicated that this might help keep the viewport clear).
I
> have some concerns that the blower may be to noisy and not efficient at
the
> reduced flowrate caused by the head loss across the absorbent.  If it is
to
> loud, I will look or another.  Maybe we can get Alec to tell us what he is
> using to circulate air in his boat?  I know he is also building his own
> system.
>
> >Also,would you use a mechanical or electronicpressure
> > sensor?
>
> I am using 600-1100mbar barometric pressure sensor from Omega (
> PX2760-600A5V  ). This sensor has an accuracy of  +/- 0.25% span  with 0.1
> to 5.1 VDC signal output (3-wire). Because I am using a PLC, I can bring
the
> cabin pressure signal in as an analog input and send out from the PLC a
> digital output that activates the O2 solenoid valve.
>
> If you find an off the shelf scrubber system for small cabins, please
post.
>
> On a previous thread, did you every find and test a solution for your
> problem of air bubbles sticking to your bow viewport?
>
> Cliff
>