The Electrolung Rebreather

The following pictures and information were contributed Walter Stark, the designer of the Electrolung. He is a rebreather list member.

Excerpt from Rebreather list posting "Electrolung design VI. Final (Reflections and speculations)"
Jul 21 1998

Development of the Electrolung came about through the chance meeting of John Kanwisher and I aboard Ed Link's diving research vessel in the Bahamas in early 1968. Ed was trying out his new diver lock-out submarine Deep Diver and had invited along several researchers with relevant interests. I was there to do some deep biological collecting and John was there to do heart rate/respiration measurements on divers using some new acoustical telemetry equipment he had developed.

Lock-out dives from Deep Diver were done using hose fed OC Kirby Morgan helmets. Gas for this purpose and to pressurize the lock-out chamber was supplied from a large high pressure sphere carried by the sub. The large amount of gas required for a single dive severely limited the number of dives which could be made and involved substantial cost and logistic considerations. The need for more efficient utilization of gas was clearly apparent.

It turned out that John and I had both been considering the feasibility of a mixed gas CCRB using electronic sensors to control PPO2. We both knew in general terms what was needed but John wasn't a diver or a machinist and I didn't know that much about electronics. However, I had been diving for 15 years and had built a wide range of underwater equipment and John, in addition to being a physiologist, had invented the first polariographic oxygen sensor and held a dual appointment at Woods Hole Oceanographic Institute and MIT where he lectured on electronic instrument design.

When we returned to our homes John started putting together the sensors and control circuit and I started getting together the hardware and machining all of the necessary bits. Six weeks later we both had our respective parts together. John sent me the board and sensors, I installed them and it worked. The overall configuration and design was basically as described but there were, of course numerous details to clean up. The electronics for example were wire connected on a breadboard and the solenoid valve I had hand made and actuated with a solenoid scavenged from a battery operated coo-coo clock.

Although the prototype was put together quite quickly it was far from a "first thing which comes to mind" effort. Quite a few years experience and thought had led up to it so that when actual construction was began we both knew pretty clearly what needed to be done and how to do it. Later at Beckman I had the opportunity of working with a whole group of specialists on improving the same device. The outcome was some tidying up of details but no fundamental improvement. The biggest problem was to prevent the creation of problems which didn't previously exist but could be introduced through changes made by specialists who were unaware of consequences outside of the narrow area of their expertise. The experience gave me a real appreciation of both the power and the limitations of specialist expertise and the importance of systems analysis in coordinating and integrating the input of specialists.

Although development of the Electrolung was interesting, even exciting, in itself it was just an interesting incident in a bigger, far more interesting and significant picture. Like most historical events, I suppose, what was happening didn't appear to the participants at the time so remarkable as it later does in the broader perspective of hindsight. The larger perspective on what is taking place right now tends to be somewhat obscured by the ordinary events of living. Except for rare instances whatever we are doing, however interesting and exciting it may be, tends to still feel like life, not like history in the making.

Click on any image to get a full size image with the associated description.

Polariographic oxygen sensors. Left, bare sensor.  Middle, sensor with silicone rubber boot pushed half-way down over teflon membrane.  Right, sensor and boot in sensor holder.   Boot O.D. and hole in holder are tapered for snug fit. Cathode (center) is platinum. Anode (outer) is silver.  Electrolyte groove is between.  Body is epoxy. Electronics section.  Solenoid and sensors at left, wrist display above.  Leads to wrist display are inside hose covered by SS braid connecting to electronics section at ambient pressure. Main circuit board.  Front modules contain amplifiers for each sensor including zero and gain trim pots on front.  Module behind controls solenoid.   Silica gel canister and double throw power switch is at top.   Push button momentary-on switches at right were a later addition enabling pre-dive battery check under load using the wrist display meters to read.  Previously this was done using an external meter. Battery holder and base plate (sponge rubber pad has come loose from base plate in photo).  Audible alarm is at right.  This is on opposite side of longitudinal bulkhead from the electronics.  Connection for O2 to solenoid is at lower left. Wrist display of three edgewise panel meters.  Construction is teflon coated cast aluminum with o-ring sealed 1/4" acrylic face plate held in place by a large circlip. High pressure needle valve for control of inert gas supply. Oxygen regulator and bypass valve.  Spring loaded cover over bypass valve actuator is being help up. Mouthpiece valve assembly viewed from front.  Mouthpiece mounts at top back.  Close-off is actuated by lifting lever at right.  Bottom hose goes to counterlung.  Right and left hoses go to and from absorbent canister. Mouthpiece parts. Body is teflon coated cast aluminum, other parts PVC.   Threaded parts are sealed with non-acidic silicone sealant.  Inlet check valve is in PVC part at left.  Outlet check valve is inside body just above hose connection at middle right.  Close-off valve is at top. Counterlung.  Hose connection is near center, drain at lower right.   Grommets for attachment at corners.  Material is a fiber reinforced translucent plastic.  Probably vinyl. Counterlung details.  Bar on inner collar of hose fitting is to prevent  possible stoppage of gas flow by the opposite side of the counterlung covering the opening while gas still remained in the upper part of the bag.  Note welded seal near edge of bag.  All hose fittings on the Electrolung had a groove like this one.  The groove is beneath where the hose clamp goes and hose material is squeezed into the groove by the clamp making for a much more secure attachment than a smooth surface. Backpack viewed from behind..  Inert gas cylinder on left, O2 on right, absorbent canister between.  Electronics section at top.  Breathing hoses attach on opposite side just below electronics bulkhead. Bottom of absorbent canister.  Note spring loaded bulkheas and screen to retain absorbent, central gas inlet tube from above and tie rod which threads into top of electronics section holding everything together. Top of absorbent canister looking into space where sensors and solenoid fit when assembled.  Inhaled gas comes in on right, down the central tube to the bottom, then back through the absorbent, past the sensors, and out to the mouthpiece via the opening on the left.  Note top absorbent bulkhead in background and threaded top end of central tie rod in foreground. The shoulder in main cylinder is because acrylic tubing varies somewhat in size and we machined it out to a standard I.D. so the electronics bulkheads and end closures could be made to a standard size. Front side of Electrolung backpack showing shoulder and waist strap arrangement.  Adjustable tabs carrying the twist studs for attaching the counterlung at the shoulders and waist provided for its positioning adjustment. Diver with Electrolung.  Note pink Barylyme absorbent.  Acrylic bubble was being used for shark cage. Electrolung in use.  Bahamas 1970.

Copyright © Northwood Designs, Inc. All rights reserved.
Revised: September 07, 2005.