Breathing circuit

Three breathing hoses were attached to the mouthpiece. One went straight down to the counterlung which was worn on the chest. The other two went to either side over the shoulders to the inlet and outlet of the absorbent canister/electronics section which was worn on the back. Initially hoses from the old style twin hose scuba regulators were used. At Beckman we found a manufacture in L.A. who made high quality fiber reinforced hoses for the O2 breathing systems in military aircraft. The price was only a little more than the scuba hose and they could be made to order as to length in small quantities. Scuba hoses tended to start to leak after a year or two. The others are still usable after a quarter century in tropical conditions.

Hose clamps may seem mundane but are worth considering. A hose coming off with scuba is an inconvenience. With a RB it is a life threatening disaster. Initially we used the spring steel ratchet type clamps used on scuba regulators but I didn't fully trust them and they rusted. We tried chrome plating them and found they would then break unexpectedly due to hydrogen embrittlement. In the end we went to good quality heavy duty SS worm screw type clamps. Some SS clamps have ordinary mild steel worm screws which rust, electrolyze, and break after awhile in marine use. Light weight SS clamps can also break for no apparent reason due to stress fatigue. SS is prone to this. SS fitting used in sailboat rigging are notorious for letting go at the most inopportune times.

A lot of people seem to now use the nylon ratchet type ties for clamping hoses but I wouldn't trust these either for critical applications. Nylon is subject to cold flow under stress and after a while they become looser. Using them as a back up next to a good SS clamp however, might not be a bad idea.

The counterlung was a bag made of two pieces of plastic material electronically welded together over a 1/4" surface around the entire perimeter about 1/2 " in from the edge which was then sewn together wrapped in a heavy edging tape. Originally I used clear vinyl for the material. This worked well enough but later I found a lighter, more flexible, translucent fiber reinforced plastic material which was better.

Being clear or translucent offers two advantages. It lets light in and so reduces the growth of micro-organisms. It also makes it easy to see if any water has accumulated and get rid of it before it gets to a level where it might be drawn into the absorbent canister. Places which make awnings, boat covers, etc. or those who make plastic zipper bags ,folders and the like can easily and inexpensively do this kind of work. All you need is a paper pattern of what you want. One-offs for prototyping are not expensive and with a $100 or so for a die for the welding they can pop out small quantity runs dirt cheap. Usually they also have samples and catalogs of all sorts of material to choose from. Teflon coated nylon is now available and might be very good for this application. I mention all this because some homebuilders may be interested.

The counterlung had a single hose attached about 1/3 of the way up from the bottom on the front (away from the body) side. A drain plug was at the bottom near the lower left corner. At Beckman we added an overpressure relief valve near the top. The fittings all used a flange and threaded collar type attachment similar to a kitchen sink drain. The flange incorporated a groove and o-ring in its face which ensured a firm grip and seal with the counterlung material. The fittings were machined from PVC except for the small drain fitting which was SS or chromed brass with a 1/4" plug on a short lanyard. It was basically the same as a control gland used in underwater camera housings.

The overpressure relief valve released at somewhere around 0.75 psi. Its only practical use was the prevention of possible counterlung rupture if gas was accidentally valved in with the mouthpiece shut-off valve closed. It was introduced at the suggestion of experienced OC divers who not being used to getting rid of excess gas via the nose during ascent tried to exhale against a full counterlung and couldn't.

The counterlung was attached by grommets at each corner which mated with twist studs mounted on the shoulder straps at the top and on short adjustable straps paralleling the backpack waist strap on each side at the bottom. The counterlung volume we used was about 4 L.

There has been some discussion on the list recently re: the relative merits of chest mounted (resistance on exhale) Vs. back mounted (resistance on inhale) counterlungs. In an earlier post, which has been quoted in the recent discussion I opted for chest mounting as preferable because the mechanics of breathing musculature is such that the power available for exhalation is greater than that for inhalation. The counter argument is that resistance on exhale reduces the volume of exhaled gas leading to CO2 retention.

First, we need to keep in mind all this is somewhat hypothetical and in the real world both configurations have been used successfully. With sustained high level exertion where any advantage might be important (and in the continuing absence of any proper comparative testing) I would opt for the chest mount for two reasons. It's less tiring to put a bit of extra effort into exhaling than it is into inhaling and the bottom line at the extreme for ventilation lies with how much gas you can move in and out in a given time. Given equal resistance in either direction the more powerful exhalation cycle will move the greater amount of gas. In the end, over a few breaths, expiration and inspiration must be equal. Restriction of either sets the limit so if there has to be a restriction I would rather it be on the side which can best handle it.

We sold a number of Electrolungs to commando type users. One of their prime concerns was breathing resistance in sustained hard swimming. After trying it, all gave it their thumbs up in this respect. In out of water chamber tests at 1000 FSW pressure breathing resistance during exercise was encountered. This was in the breathing circuit itself and could of course be relieved somewhat by bigger hoses, larger absorbent bed cross section, etc but as the market for that capability was effectively nil it was never pursued.

One memorable experience with the commando types took place in the Bahamas. A British Royal Marine Commando attached to the Canadian Navy flew down to join me on my vessel and try out the Electrolung. He was a big bullet headed guy, built like a fridge with a head. After a couple days instruction diving he wanted to do a long hard swim with it and as there was no one else to do it with him I ended up going along. He went for a couple of miles virtually flat out. Luckily the water was crystal clear so I managed to at least keep him in sight. When we came to the surface the bastard wasn't even winded. He was satisfied it could do the job and just wanted a smoke. It was flat calm and the water was only about 30 feet deep so I had a skiff following us with his smokes and we could ride back.

Although I still don't know for absolute certain whether chest or back mount is optimal I do know that chest mount is good enough. What I really do like about it is that it is easy to see if there is any water in it and easy to pull the plug, squeeze the bag, and expel it.

We did have a couple of experienced OC divers, new to the Electrolung, let water leak in around their mouths until it was gurgling away with each breath. They continued until they had largely flooded the absorbent canister and eventually got a mouthful of absorbent cocktail. They were quite irate about all this and swore it was the fault of the Electrolung. This kind of thing is a recurrent problem with RBs. Experienced OC divers have habits which don't go with RBs. They also tend to think of themselves as expert divers rather than as novice RB users. As a result they often don't really listen and take advice well and tend to blame the device if anything is not right rather than realizing that they have to learn to use it right.

The actual breathing circuit for the Electrolung was: Exhale directly to counterlung via bottom mouthpiece hose. Inhale draws gas from counterlung back out the same hose into left mouthpiece hose thence to the bottom of the canister via a central tube inside it. At the bottom the gas emerges into a plenum which distributes it over the inlet surface of the absorbent column. After passing through the absorbent it emerges at the top into the chamber where the sensors and solenoid are located. From here it continues via the right mouthpiece hose into the mouthpiece itself.