Diver Dave's Minimum/Bailout Rebreather

Diver Dave's "Minimum- Rebreather"

OK, Divers: Here are some photos of a project that I've been working on for over a year now. It's a test-rig designed to prove and test the concept of a chest-worn bailout rebreather that's intended to be worn by a CCR diver to act as a second loop in time of a total loop failure. The concept is to allow the second loop to be fed from the main rig's on-board gas supplies, although I'm sure someone will want to supply it with additional gas. I wanted to be able to conceptually test the system, and to do physical tests of work of breathing, duration, and physical system component layouts without needing to drag out my Mark-15 for shallow and mid-depth trials. I then chose to make up a simulated "Mark-15" gas supply and mounted it on my back. Originally the rig was fed with (2) drysuit inflation valves, one on each side fed respectively with diluent (left) and 02 (right), and that's the way that the "bailout" rebreather will be manufactured. This means that you simply will need to run one quick-disconnect hose from both diluent and 02 on your main rig to feed the two manual add valves on the bailout rig (drysuit valves, as used by the Inspiration as main manual add valves) and then your bailout rig is a simple manually run CCR. That system worked very well. Sadly, I didn't take any photos of the system before I re-modified it into a KISS system "Minimum-rebreather" for use as an intentional diving system. The bottom line is that the bailout system worked so well that I found it to be entirely suitable as a rebreather *by itself* and then made some changes to my test rig to make it more optimized as an "intentional" diving system as opposed to an emergency device. In order to do this, I removed the drysuit valves, made up a manual diluent add valve, and then added a KISS valve for the 02 supply. Guys, this system works GREAT. Following are the photos of the "intentional" setup, and as soon as I get another chassis from OMG, I'll make up another bailout system for photos. I need to, since at the 2002 "Beneath the Sea" show enough people saw this system that 6 guys placed orders for bailout systems without even seeing the configured bailout rebreather. The hope is that OMG will make the bailout system as a factory item, and to that end I'll be visiting their factory in La Spezia, Italy, in June (my schedule permitting) to demonstrate the bailout system and to discuss the production of same with their engineers. Well enough of the talk, here's the rig:

The rig started out as the OMG C-96 Oxygen rebreather. This rebreather, which is full described on it's own page, is a high quality pure 02 rebreather featuring a chest-worn counterlung and a fully cyclic system of scrubber operation, with a modestly sized radial scrubber.

The first change was to add an overpressure valve, this one from a Draeger Dolphin. I'm undecided at this time about this: I'm not sure if it's a help to have it (to prevent over-expansion of the counterlung on ascent), or a detriment (possible leak path). In any case, it's there now, mounted at the top of the counterlung. So far it's worked great.

The second modification was to add a P-Connector, for later PP02 measurement. This is on the left side of the counterlung. Originally, I used a drysuit inflator valve in this position for use as a manual diluent addition system, but when I re-modified the chassis for intentional diving, that became redundant.

The reason that a second gas-input path became redundant was that I decided to cut the original 02 addition line, and to add a quick-disconnect line to that port which will allow me to add either 02 or diluent into the counterlung, through the same port. The quick-disconnect makes dressing into the rebreather easy, as the gas in back-worn, the counterlung is chest-worn, and the two connect in a moment when dressing to get into the water.

Just a short preview of the system, as described more fully below: Both 02 and diluent are fed into this combining manifold (between the two gas supply cylinders on my back) and then are supplied through the line leading from the left in the photo to the counterlung connection pictured previously. The two inlets to this manifold are also quick-disconnect lines, for ease of setup pre-dive.

The only other modification to the actual chassis is the addition of webbing with Fastex connectors at both the shoulders and the waist to allow the completed rig to be clipped onto the existing harness already worn by the diver. In use as a bailout system, that would be the original harness of the "donor" rig. In the intentional diving system, it's the harness for the backplate to which is attached the (2) small supply cylinders. Although the original 02 bottle position is not used, I decided not to cut off the little pocket for the cylinder (although it would be easy to do), as I "may" want to use that spot to carry a small Argon cylinder for my drysuit. We'll see.

For the intentional use system, I made up the diluent addition system by using a Poseidon 5000 first stage, run to a manual add valve manufactured from a modified BC inflator, and then that feeds a normal quick-disconnect hose which will be connected to the gas combining manifold.

This homebuilt add valve requires a little explanation in itself. At first, it would seem easy to modify a BC inflator. The trouble is that no epoxy that I've found bonds to the material the inflator is made of, and when trying to O-ring seal the inner brass spool used to modify the valve it was found that the interior dimensions of the valve are not precise enough to allow O-ring sealing. The fix is to chuck the valve in the lathe and then to use a boring bar to machine the interior bore of the original valve to a true cylinder. Then an O-ring sealed spool may be fitted. This only took 3 tries before it was correct.

Now things are starting to fall into place. This is the diluent add system fitted to the cylinder (a 13 cubic foot Faber cylinder) with the return feed-line coupled to the gas combining manifold. The cylinders are mounted to an old aluminum backplate I had in the shop here, and the gas combining manifold is attached to the backplate between the two cylinders.

Next is the 02 addition system. This was made using components sourced from Gordon Smith, and as used in both his superb KISS rebreather and my own Franken-Son. This is a proven system, and works great. For those new to the system, it flows a small trickle of 02 into the loop at slightly less than the divers metabolic use rate, thus increasing the time duration between required manual 02 additions. Since it also has a manual addition button included, it's an obvious choice for making up such systems as this.

The system requires a constant pressure regulator, not one that is responsive to ambient pressure. You can see the machined Delrin plug that's been installed to block the ambient pressure chamber of this Apex first stage. Since there's no provision for any other overpressure relief in case of a high pressure seat failure, I also added an overpressure relief valve here. On the diluent side, that is taken care of by an open circuit second stage (bailout regulator) which I have not shown for reasons of clarity. In order to follow my requirement of the cleanest possible system, I also decided to use button-type high pressure gauges on both cylinders. I don't need to read either 02 or diluent pressures while diving, as there's lots more than I can use for any reasonable duration dives.

Here's a detail of the KISS valve. Basically, I run the 02 supply from the first stage through an isolating valve, then through a 15 micron filter, then into the KISS valve, and then back to the rig through the gas combining manifold. The reason for the isolation valve is to secure 02 flow pre-dive, so it's not increasing the PP02 as I sit waiting for the boat to be anchored, and also to terminate 02 flow in the case that the first stage fails and increases it's pressure, which would raise the PP02 to potentially toxic levels. The valves on the little cylinders on my back are *really* hard to reach due to the fact that they sit quite low on my back, so turning off the main cylinder valve isn't really feasible. This system works great.

Now we have both diluent and 02 addition systems added to the backplate. One hose feeds over each shoulder. Now we just need to get into the "doubles", clip on our counterlung/scrubber combination, attach one quick-disconnect hose, and jump into the water.

Top view of the "doubles", showing the two regulators and the feed hoses going to the manual add and KISS valves and back to the gas combining manifold.

Some "doubles", eh? Especially when considering that they provide the same gas duration as TWO sets of double 104's when dived in 130 feet of water (!).

Manual diluent addition lays on the left chest, secured by surgical tubing.

02 addition system is a mirror-image of the diluent add system, only with the isolation valve as well.

Here's the divers-view of the chassis ready to be clipped onto the harness. Two Fastex buckles at the waist, two at the shoulders. Plug in the quick-disconnect line and go.

Here are the waist-clips being attached.

Followed by the shoulder clips.

3-sensor PP02 meter originally made for Franken-Son is clipped on, with surgical tube on left shoulder. For bailout use, I used a single sensor system, but for intentional use 3 sensors are the way to go.

Lastly, the gas feed hose is connected to the counterlung with the quick-disconnect hose that's fed from the gas combining manifold.

All dressed up and noplace to go. I've dived this rig on and off for a year, and it's been a real pleasure. You can see how clean and light the entire system is, and it's very simple to use. At first glance the front mounted counterlung and scrubber might seem to be awkward, but in the water you don't even know that it's there. For those requiring a bit more abrasion protection, OMG now makes a Kevlar outer-bag to protect both the counterlung and scrubber from cuts and abrasion, although I don't choose to use it.

Not the best photo of me, but here's the profile of the rig. It's VERY streamlined, and is a pleasure to dive. I normally run drysuit and bailout from the on-board diluent cylinder, but if I did any real decompression diving with this rig alone I'd carry more gas, probably by simply using a larger diluent cylinder. But remember, it was designed as a *bailout* system for a Mark-15, not as an intentional diving system. The fact that it works so well as an intentional diving system is just icing on the cake.

That's it for now. I think that if you study this system, that you'll see the beauty of using it as a modular system. Use it "stand-alone" for mid-depth diving, and in conjunction with a "Main" rebreather as a bailout system for extreme diving. I'm going to play with using the KISS system for this in conjunction with my Mark-15 as opposed to using the drysuit valves for completely manual 02 addition, but this will require a HP line from the Mark-15 to the modified Apex first stage, as the KISS valve needs a constant pressure regulator to provide constant 02 flow. That ought to not be too hard to do, I just need to find a smart place to locate that first stage. This is a project "under development" so stay tuned.

That's all folks! Take me Back to the Projects!

		The rig started out as the OMG C-96 Oxygen rebreather. This rebreather, which is full described on it's own page, is a high quality pure 02 rebreather featuring a chest-worn counterlung and a fully cyclic system of scrubber operation, with a modestly sized radial scrubber.
		The first change was to add an overpressure valve, this one from a Draeger Dolphin. I'm undecided at this time about this: I'm not sure if it's a help to have it (to prevent over-expansion of the counterlung on ascent), or a detriment (possible leak path). In any case, it's there now, mounted at the top of the counterlung. So far it's worked great.
		The second modification was to add a P-Connector, for later PP02 measurement. This is on the left side of the counterlung. Originally, I used a drysuit inflator valve in this position for use as a manual diluent addition system, but when I re-modified the chassis for intentional diving, that became redundant.
		The reason that a second gas-input path became redundant was that I decided to cut the original 02 addition line, and to add a quick-disconnect line to that port which will allow me to add either 02 or diluent into the counterlung, through the same port. The quick-disconnect makes dressing into the rebreather easy, as the gas in back-worn, the counterlung is chest-worn, and the two connect in a moment when dressing to get into the water.
		Just a short preview of the system, as described more fully below: Both 02 and diluent are fed into this combining manifold (between the two gas supply cylinders on my back) and then are supplied through the line leading from the left in the photo to the counterlung connection pictured previously. The two inlets to this manifold are also quick-disconnect lines, for ease of setup pre-dive.
		The only other modification to the actual chassis is the addition of webbing with Fastex connectors at both the shoulders and the waist to allow the completed rig to be clipped onto the existing harness already worn by the diver. In use as a bailout system, that would be the original harness of the "donor" rig. In the intentional diving system, it's the harness for the backplate to which is attached the (2) small supply cylinders. Although the original 02 bottle position is not used, I decided not to cut off the little pocket for the cylinder (although it would be easy to do), as I "may" want to use that spot to carry a small Argon cylinder for my drysuit. We'll see.
		For the intentional use system, I made up the diluent addition system by using a Poseidon 5000 first stage, run to a manual add valve manufactured from a modified BC inflator, and then that feeds a normal quick-disconnect hose which will be connected to the gas combining manifold.
		This homebuilt add valve requires a little explanation in itself. At first, it would seem easy to modify a BC inflator. The trouble is that no epoxy that I've found bonds to the material the inflator is made of, and when trying to O-ring seal the inner brass spool used to modify the valve it was found that the interior dimensions of the valve are not precise enough to allow O-ring sealing. The fix is to chuck the valve in the lathe and then to use a boring bar to machine the interior bore of the original valve to a true cylinder. Then an O-ring sealed spool may be fitted. This only took 3 tries before it was correct.
		Now things are starting to fall into place. This is the diluent add system fitted to the cylinder (a 13 cubic foot Faber cylinder) with the return feed-line coupled to the gas combining manifold. The cylinders are mounted to an old aluminum backplate I had in the shop here, and the gas combining manifold is attached to the backplate between the two cylinders.
		Next is the 02 addition system. This was made using components sourced from Gordon Smith, and as used in both his superb KISS rebreather and my own Franken-Son. This is a proven system, and works great. For those new to the system, it flows a small trickle of 02 into the loop at slightly less than the divers metabolic use rate, thus increasing the time duration between required manual 02 additions. Since it also has a manual addition button included, it's an obvious choice for making up such systems as this.
		The system requires a constant pressure regulator, not one that is responsive to ambient pressure. You can see the machined Delrin plug that's been installed to block the ambient pressure chamber of this Apex first stage. Since there's no provision for any other overpressure relief in case of a high pressure seat failure, I also added an overpressure relief valve here. On the diluent side, that is taken care of by an open circuit second stage (bailout regulator) which I have not shown for reasons of clarity. In order to follow my requirement of the cleanest possible system, I also decided to use button-type high pressure gauges on both cylinders. I don't need to read either 02 or diluent pressures while diving, as there's lots more than I can use for any reasonable duration dives.
		Here's a detail of the KISS valve. Basically, I run the 02 supply from the first stage through an isolating valve, then through a 15 micron filter, then into the KISS valve, and then back to the rig through the gas combining manifold. The reason for the isolation valve is to secure 02 flow pre-dive, so it's not increasing the PP02 as I sit waiting for the boat to be anchored, and also to terminate 02 flow in the case that the first stage fails and increases it's pressure, which would raise the PP02 to potentially toxic levels. The valves on the little cylinders on my back are really hard to reach due to the fact that they sit quite low on my back, so turning off the main cylinder valve isn't really feasible. This system works great.
		Now we have both diluent and 02 addition systems added to the backplate. One hose feeds over each shoulder. Now we just need to get into the "doubles", clip on our counterlung/scrubber combination, attach one quick-disconnect hose, and jump into the water.
		Top view of the "doubles", showing the two regulators and the feed hoses going to the manual add and KISS valves and back to the gas combining manifold.
		Some "doubles", eh? Especially when considering that they provide the same gas duration as TWO sets of double 104's when dived in 130 feet of water (!).
		Manual diluent addition lays on the left chest, secured by surgical tubing.
		02 addition system is a mirror-image of the diluent add system, only with the isolation valve as well.
		Here's the divers-view of the chassis ready to be clipped onto the harness. Two Fastex buckles at the waist, two at the shoulders. Plug in the quick-disconnect line and go.
		Here are the waist-clips being attached.
		Followed by the shoulder clips.
		3-sensor PP02 meter originally made for Franken-Son is clipped on, with surgical tube on left shoulder. For bailout use, I used a single sensor system, but for intentional use 3 sensors are the way to go.
		Lastly, the gas feed hose is connected to the counterlung with the quick-disconnect hose that's fed from the gas combining manifold.
		All dressed up and noplace to go. I've dived this rig on and off for a year, and it's been a real pleasure. You can see how clean and light the entire system is, and it's very simple to use. At first glance the front mounted counterlung and scrubber might seem to be awkward, but in the water you don't even know that it's there. For those requiring a bit more abrasion protection, OMG now makes a Kevlar outer-bag to protect both the counterlung and scrubber from cuts and abrasion, although I don't choose to use it.
		Not the best photo of me, but here's the profile of the rig. It's VERY streamlined, and is a pleasure to dive. I normally run drysuit and bailout from the on-board diluent cylinder, but if I did any real decompression diving with this rig alone I'd carry more gas, probably by simply using a larger diluent cylinder. But remember, it was designed as a bailout system for a Mark-15, not as an intentional diving system. The fact that it works so well as an intentional diving system is just icing on the cake.