RE: [PSUBS-MAILIST] co2 monitor source

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

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