The SA-2, is the second functional Closed Circuit Oxygen Rebreather which I built. I had been working on a mixed gas rebreather, but became sidetracked as a friend, Ron Edmundson produced his "very pretty packaged" front mounted O2 rebreather with a scrubber canister mounted within the counterlung. It indeed is a very pretty rebreather with such wonderful color combinations as a Black breathing hose, Blue gas cylinder, and Yellow counterlung. See http://home1.gte.net/doctrbob/MIB.htm. I couldn't stand it, I had to put one together also. So after Ron left for home, (after helping me install a garage door last weekend), my feverish quest began in the construction a small front mounted rebreather package. The clock started ticking at 3 PM on that Sunday...

The purpose of this project was the get a package more "user friendly" than the original Sioux-Air, and to test the "scrubber-canister-within-the-counterlung" design. I wanted to keep the design simple (KISS), and apply some of my leanings from the first rebreather. And of course I couldn't stand it that my friend Ron made such a photogenic rebreather...I needed some new pictures myself.

Being that I had most of the materials on hand, it was pretty much of an "assembly" project, with limited "manufacturing" of original items. Not having my new lathe set up yet, I still limited the design to many parts which I can obtain off the shelf from my local home building supply stores. (I love these stores.)

Some design goals were to make the unit easy to clean and service after use, particularly the counterlung, breathing hose, and scrubber canister. Nothing worse than an old musty counterlung, which gets to smell like a gym-sock storage bag after some use. To this end I made the entire unit easy to field strip for cleaning with no special tools needed. (And the only "special" tool that is needed for "depot" level maintenance is a slotted screwdriver.)

The critical part of this unit was the design of the Counterlung Bulkhead . This part has four major functions: First, it provides the upper seal for the Counterlung, Second it is the structural support which holds the Scrubber Canister, Third it is the mount for the Breathing Hose Attachment Fittings, and Forth it contains the fitting to connect counterlung to the Harness Unit. (The Harness Unit holds the Gas Cylinder, Mounting Straps, and acts as a Chest Protector.)

I made the Counterlung Bulkhead out of marine plywood. The material was used because of ease of use and availability at the time. The wood will be protected with a moisture barrier (Aquaseal and/or neoprene cement) for initial tests, and if the design proves successful, the part will later be fabricated out of a plastic (lexan) which is more suitable for a marine environment.

The Counterlung Bulkhead was made in two parts. A smaller upper oval and larger lower oval member. The two parts are secured together with countersunk fasteners and sealed with Aquaseal at each through fitting. The double oval design was selected to (a) provide a smooth surface to compress the breathing bag upon, with a stainless steel hoseclamp, and to secure this hose clamp from movement in either an up or down direction. The larger oval will prevent movement downward, and the Harness Unit will prevent the hose clamp from moving upward. (In actuality I feel that the friction produced from the compression of the hose clamp on the neoprene bag to the wooden clamping surface would not allow any movement in either direction, but I "felt" better building it this way. And of course a production unit will have a slot/groove machined in the ''one piece' lexan Counterlung Bulkhead.)

The Harness Unit, which I fabricated first was made of a 1/8" sheet of aluminum plate. To keep the number of parts to a minimum I first rolled the end over a 3" pipe to produce a 280 degree curved area. This area will be used to secure the gas cylinder. In fact it works perfectly, no additional hardware is needed, as it snugs the cylinder securely. (I am aware to remove the cylinder from the harness for cleaning after the dive as we do not want two different metals touching while drying after a salt water bath.) A couple of additional folds of the aluminum provided the remainder of the Harness Unit. Holes were cut/drilled for the various plumbing through-items for the Counterlung Bulkhead, and other harness strap attachment points, etc.

The counterlung (breathing bag) was made of 3mm skin-one-side neoprene, glued with neoprene cement. The upper counterlung seal was made upon the Counterlung Bulkhead with a stainless steel hose clamp. The lower seal was accomplished by a couple of simple folds of the bag and a compression clamp made from a couple of wooden dowels. The lower seal is fixed to the harness.

Simple quick compression fitting from your friendly home builders supply provided the attachment for the breathing hoses. And they work great.

The Scrubber Canister was made from 4" ABS pipe. One end was sealed with an acrylic plug via screws and silicone. A hole was drilled and tapped for a 3/4" PVC connection. A spacer holding a screen was placed at this end. At this point we have a cylinder open on one end, with a plug on the other end. The end with the plug has a hole drilled at the circumference to attach a 3/4" PVC connector. This is basically the scrubber canister. Place the scrubber into it to about an inch or so from the top, place another barrier (Screen/plate) and compress the scrubber a little, to keep it from settling. (I made a spring actuated plate for this purpose.) An open cell foam is used to contain "dusting" and a sponge is place at the "sealed" end to absorb water. A few other holes were drilled in the "open" end and that is about that. One scrubber canister complete

The canister connects to both the exhale and inhale fittings on the inside of the Counterlung Bulkhead. The Design of the "plumbing" is such that exhaled gas is directed straight to the "sealed" end of the scrubber canister, the gas flow travels along the scrubber bed and exits into the counterlung. The connection of the scrubber canister to the inhale fitting is solely for mounting purposes, as gas into this fitting can come from anywhere within the breathing bag. (This side of the scrubber canister is open to the counterlung.)

A second stage regulator is also mounted to the Counterlung Bulkhead through a PVC fitting, (via clear tubing & hoseclamps). This regulator will allow the manual addition of gas to the system, or if bag collapse occurs direct demand operation will occur.

The unit was finally assembled at 9 AM on the following Sunday. Construction time 7 days. It was now off to the ocean for open water trials.

Initial system integrity checks proved successful...No leaks.

First dive test, always an exciting activity, proved uneventful. The unit is about 2 pounds positively buoyant with approx. 2 liters of gas in the counterlung. (Unit weight on land is 21 pounds, with one liter of SODASORB.) Both divers were improperly weighted, (forgot weight belts), and overall slightly positively buoyant, but were able to dive down with the unit to 10-15 fsw and comfortably perform a compass course. The unit works.

Proof of design has been accomplished.

Placing the scrubber canister within the counter lung is possible. Some benefits of this design seem to be a reduction in the number of parts, and possibly an increase in scrubber efficiency. The degree of insulation provided by the neoprene breathing bag, and having the entire canister within an atmosphere of heated exhaled breath can help to keep the scrubber at a higher operating temperature. (A more formal gas analysis is to be conducted in the lab.)

[Additional areas of research which are of interest to me concern the scrubber canister: such as what is the minimum size needed, what dwell times are required, what performance changes occur as different SLPM of gas is passed through it. I would appreciate any references to these topics, thank you.]

The following lists parts, materials and tools used in the construction of this rebreather:

Parts: CO2 Scrubber: SODASORB and/or SOFNOLIME, O2 Cylinder Regulator: O2 Cleaned/Compatible, Scott Bite Block w/ double hose

Materials: ABS Pipe, Aluminum Plate, Aquaseal, Eectrical Cable Ties and Clamps, Electrical Tape, Fasteners: SS, Brass, Nylon, Marine Plywood, Neoprene Cement, Neoprene, Nylon-one-side, Nylon Webbing, Open Cell Foam, PVC Fittings, PVC Pipe, Quick Disconnects, Silicone Seal, Springs, SS Hose Clamps, Wooden Dowel

Tools Used: Belt Sander, Circular Saw, Drill Press, Files, Knife, Saber Saw, Sandpaper, Scissors, Screwdrivers, Socket diver

Other equipment: Computer to aid in Design, Sewing Machine

Note: Diving with Closed Circuit Rebreathing Equipment is much different, and much more dangerous than diving with Open Circuit SCUBA Gear. I do not recommend the home construction or use of such gear. This article is provided for your entertainment only. I will not be held liable in any way shape or form for someone's morbidity or mortality resulting from the use of, or indulging in any of the above mentioned activities.