A passive addition oxygen rebreather from Australia
A small explanation for those readers who are still unfamiliar with the passive addition system. Most oxygen rebreathers use a constant mass valve or a manually operated system. However, Mike’s rebreather is equipped with a passive addition system. In this system, the counter lung is exhaled and at a certain point a specific pressure is reached in relation to the ambient pressure. When that pressure is reached, a diaphragm valve (demand valve) will activate a valve and add oxygen to the counterlung until the ambient pressure is reached again. The diver does not have to do anything but breathe. The system automatically supplies new oxygen when a certain amount is used up. Hence the name Passive addition (JWB).
Mike Down from Australia send me these great pictures and story about his unit.
This LAR is really something. Wouldn’t it be lovely to dive 3 hours in Australia!
Greetings Jan Willem,
Hope all is well with you and that you are getting some time to dive and enjoy the wonderful underwater world.
Winter here in South Australia, cold, wet, windy and poor visibility so I am waiting for some better weather.
Meanwhile, have been building a few different bits of gear to play with this summer, one being my Nu-LAR 6.
I had a nice clean LAR 6 PU shell, a new LAR 5 demand valve still in its sealed bag, a LAR 5 breathing bag and
a couple of new Dolphin scrubbers.
I soon changed the ‘P’ connectors on the scrubbers to the female version, hacked into the breathing bag and fitted
a female ‘P’ connector, machined up a male ‘P’ connector, fitted that and then started on the plumbing.
I had two neat special combination valve/1st stage regulators left over from another project so I fitted them to Luxfer
1 litre cylinders, and then I needed to machine up an adapter to run the contents gauges the right way so that they would sit
flush with the side of the LAR casing.
I then fabricated the gas line from 3mm annealed copper tubing, made up LAR style quick release M12 x 1 fittings
silver soldered them to the tubing, changed the IP of the first stages to 5 Bar, hooked it all up and checked for leaks.
Once everything was tested I had the parts electroplated and reassembled the unit.
Rather than borrow a LAR hose set from one of my other units I used spare hoses that Martin from Tec Me
had supplied me, made up my own connectors and used a mouthpiece that I purchased at an auction.
It actually feels easier to use than my other LAR 6, I can quickly swap out the oxygen supply module, replace the
scrubber and be back in the water for another 3 hours. Better still it weighs less than the original and parts are much
easier to obtain than Draeger bits.
All the best
Mike
Mike, thanks for sharing this nice information!
Therebreathersite was founded by Jan Willem Bech in 1999. After a diving career of many years, he decided to start technical diving in 1999. He immediately noticed that at that time there was almost no website that contained the history of closed breathing systems. The start for the website led to a huge collection that offered about 1,300 pages of information until 2019. In 2019, a fresh start was made with the website now freely available online for everyone. Therebreathersite is a source of information for divers, researchers, technicians and students. I hope you enjoy browsing the content!