My Modifications and how it all got started


If you cant get your head around your own rebreather, you wont get your head around mine!

If for any reason you copy or Use any of my ideas for yourself, then you do so at your own risk.

i will not be responsibile for your actions

Make no mistake you are messing with life support systems,



My rebreather, only having dived it standard 3 times, this is what
I used to dive my rebreather on a 7 litre cylinder and enjoyed it but it was a little too
wide having mounted it sideways across the back.
However I did get some good bottom times with this system, but I wasn't happy
with it as it still needed refining.
I dumped the first stage fitting as it was a pain the and replaced the
first stage fitting with a 200bar din male. See picture left of tank valve and Din
conversion. If you click on the picture you can also see the thread sizes for both the
tank valve and din male fitting.

I brought 2x 5 litre Faber tanks complete with din
valves and they were much better.
I added an oxygauge and a metering valve in series
with the jetting and doubled my tank duration without a problem.
I found I could run higher mixes deeper because
I could drop the flow back with the metering valve on the fly...this worked well but I did have to watch the bag volume, ie bypass valve as I could spike the mix!


I dived this configuration for about three months before biting the bullet and designing a modification for my rebreather to go fully closed.
I found this the best way to dive, and now wont dive it any other way.


To do this I brought 2x 2.6 litre alloy tanks with din valves 200bar rated.
I designed and built 2x tank mounts to bolt onto the shell of my Dolphin along with a
proper carry handle on the back. Watch the original handle as it will in time crack your
shell. This mount has been so good that I would miss it if I ever took it off.

Below is the tank mounting system to the shell, I clicked this picture while I was still mounting it.

Next I added 2x Poseidon first stage regulators with din fittings and o2 cleaned both
for up to 100%. One for dilutant and the other for 02 and o2 cleaned one of the
tanks and labelled it accordingly.
You can see in the pictures below the completed tanks mounts and also the Poseidon
first stage regulators.
Here is a photo of the reusable hose fittings that I used to make up all the fittings.
They disappeared off the market here in Oz but I was told just the other day that they are available.

I then designed the dilutant addition by using the
existing bypass valve as it was already there so
might as well use it....since taking this photo
I have added Gordon Smiths "KISS" system to
the demand valve housing, and is covered in a separate page.
I found that the spring in the bypass valve was design
for 16 bar line pressure and I was using 8.5 bar so it was
replaced with the spring from the demand valve of a US divers
Con shelf SE regulator and this worked beautifully, I could open it with ease no matter fast I descended. This next shot shows the dosing head in place inside the harness and shell.
Please note see photo above  that this has since been changed and the dosing head now resides between the two hose connections on the back shell, and has proved to be much better. However I have left this shot on the page to show how it used to be piped up.
The contents gauge for the dilutant is over the shoulder and clips to the D ring on right hand
side of the harness.

I also took a feed from the diluent first stage and brought it over the shoulder and across
to the left hand side and used an Air2 as a bailout and BC inflation...this is a godsend.
See in the above shot I have dragged it out and you can see it attached to the Air-2.

I designed the o2 injection using a Clippard Minimatics MJV-2 two port upstream
valve and o2 cleaned it, put it in series with the needle valve seen here attached to the body of the Clipphard bypass valve.

Flow rate at 8.5bar first stage pressure was 10 litres per minute, this means that it would take approx one minute to fully flush the loop if for some reason the valve jammed open I would have plenty of time to fly the rig if needed by using the tank valve. Nice and simple backup ..remember you have to keep it all simple! Contents gauge is over the left shoulder and lies next to the Air2 and is easy to see.

O2 addition is by Gordon's Kiss method and manual add and I find now after many hours that I can fly the unit almost without instruments...I would never do this but it is very predictable and it only takes one or two shots of o2 for every 45 minutes to keep the ppo2 stable.
Quite often I find I can go up to one hour without adding any additional O2 to the loop.

Lastly I added 2x oxyguages to the rig and have them programmed to low setting .35
and high setting 1.4 and I fly the unit around .9 - 1.0 most of the time.

And that's my system, I have chosen to supply you with pictures so you can see what its all about but I'm sure you wont have any problems understanding how it all works. Here is a picture of my rebreather with its shell removed for you to look at.

I might add that since this photo was taken I have added Gordon's Kiss system to the rig and am now working on more juicy mods which will probably mean another re-write of this page. I am now a CCR convert and will never change the unit back to SCR. Duration is 10-12 hours so I can take the rig diving for a weekend and never have
to worry about tank fills and of course there is "No Mixing". Two rebreathers have now been built and they perform exactly the same with an average gas consumption of 10bar per hour, meaning it is not uncommon to go for a days diving with 60 bar of O2, however I do-not encourage this! I brought a third 3 litre tank and I use that for Helium plus air for deep dives, this replaces the air dilutant  and BC inflation is taken from my 5 litre Faber's one on each side
Air bailout on the left and and a 60 mix for deco on the right.
Funny thing is that I have been having so much fun with marine life around the inshore reefs where I live in North Queensland that I have not taken the rig past 30 meters, that's 100 feet in the imperial measure.
I had ideas of a new shell and have produced an experimental unit but time
and money have beaten be to its completion.
Instead I have replaced the original BC with my old faithful Sea Quest Black Diamond.
Since these photos were taken I have upgraded the BC to the latest Black Diamond
with what I can only describe as OUTSTANDING RESULTS.
This is one of the nice things about this system as you can place any B.C. on the
rebreather using the "A" frame.
To fit it up to the rebreather shell first I had to make up a frame.
See picture
If you look closely you will see a slot in the centre towards the top of the picture. This is where the second half of the frame which is attached to the BC fits into.

Once I had the frame fabricated it was easy to bolt up to the old holes left from
the original shell. I used 316 grade stainless steel and because I did not have access to a Tig welder used silver solder and found it to be very strong and easy to weld together.
Once I had a basic frame around the shell the rest was simple, I made up an "A" frame and mounted this to the back of my Black Diamond BC.
See picture below

This bolts straight up to the BC as it already had holes for mounting twin tanks so a simple "A" frame was no problem to bolt up. I sweated nuts onto the other side of the "U" bends to make it easier to attach and remove, also the original tank straps stay in place and don't get in the road so in a few minutes the BC cant be put back to standard for a normal scuba tank.
This is what the finished frame looked like see below.
Here is another shot of the shell and BC mating up together.

As you can see it is just a matter of tilt and slide into position, then fit and tighten the two stainless steel dome head bolts to the bottom of the shell these can be seen better in the picture of the completed frame.

And there it is the rebreather mounted up to the Sea Quest BC
Below is my dive buddy Frank Feather modelling the set-up.

Next came the pool testing of the new configuration which went extremely well finding that
I did not need as much lead weight as with the original BC.
One of the nice things with the Sea Quest is it has 50 pounds of lift and a nice weight integration system.
The  weight of the stainless steel frame offsets some of the positive bouenceny of the counter lung and it was good to see also that when the unit was floated by itself that it sat vertical, this would make it easy to don in-water should the need arise.
Since these pictures were taken I have added a little bit of weight to the shell, to offset the extra chest buoyancy when wearing a wetsuit.
It's tough diving in the tropics;-))

Ok that concludes for the moment all of the mods that I have done to my rebreather
for the time being ;-)) For more information

Go to the Final Dolphin pages to see what the completed unit now looks like and the final changes that make the rebreather what it is now.

Copyright©2001,2002 Tubbies Rebreather Pages


back to top of page