Closed Circuit O2 Rebreathers and Training?

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OTF

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Fascinating informative thread! You guys are awesome. I sometimes fantasized about getting or building a pure O2 rebreather for long shallow photography dives, but now I see why nobody seems to do that.
 

Angelo Farina

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In this document you find a short history of ARO equipment, both in Italian and in English:
https://www.hdsitalia.it/wp-content/uploads/2020/04/025-HDSN25.pdf
Then there is also an interesting article by Fausto Rambelli describing the ARO unit developed by Hans Haas in 1942, in cooperation with Draeger, which was much more advanced than Italian units (loop circuit, back mounted). He (and his wife Lotte) was using it down to 20m, without an additional BCD and without air dilution! He even says that breathing oxygen is much less dangerous than breathing air...
 

jale

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Fascinating informative thread! You guys are awesome. I sometimes fantasized about getting or building a pure O2 rebreather for long shallow photography dives, but now I see why nobody seems to do that.
In fact a lot of people ("lot" is relative :)) do that.
Personally, I started by a mod on a RG-ufm (east German escape tank rb if I remember correctly :)) then a mod on a Soviet IDA59 (sub escape rb), then playing with a Dolphin canister.
Now, beside owning a C96 and two pendulum units (so 2 pendula? :) :)), I am playing with a Ray canister and a water bag to have a kind of SM rb (something like half of a Sidewinder).
Nowadays with internet and Tecme or similar sites, it is easy to built or to assemble an unit.
But really pay attention about that you are doing
 

jale

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In this document you find a short history of ARO equipment, both in Italian and in English:
https://www.hdsitalia.it/wp-content/uploads/2020/04/025-HDSN25.pdf
Then there is also an interesting article by Fausto Rambelli describing the ARO unit developed by Hans Haas in 1942, which was much more advanced than Italian units (loop circuit, back mounted). He was using it down to 20m, without an additional BCD and without air dilution! He even says that breathing oxygen is much less dangerous than breathing air...
Thanks for the doc. Indeed Sanosub P96 (P for Pendulum) and Castor P96 then Sanosub C96 and Castoro C96 pro... different companies, small mods, not much differences if only quality built as OMG seems to have a better reputation.
Angela, during your ARO training, which unit did you use?
 

Angelo Farina

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Just to split hairs, it seems to me that telemonster's unit is not a MK4 as it doesn't have the ADV on the bag (or at least I don't see that) but a C96 with the large canister.
Can you, Angelo, confirm that and also that I said before about the two versions of the C96. One with a small metal canister sold now by Sanosub and the new version with a large canister (the one telemonster has...I think).
Or maybe, we have just the same name for different units...a bit lost right now :)
The automatic oxygen injection on the Caimano IV is standard on the pure-oxygen version, but has been removed in the "deep ARO diving" version he has got, as it is dangerous to have automatic oxygen injection when using the system below 6 meters...
As said, the telemonster's unit looks to me as the military-grade unit which was only sold to Italian Comsubin incursors, and which is not possible to buy by normal recreational divers.
The main evident difference between Castoro and Caimano units is that in the Castoro the tank's valve and injection hose are on the left, whilst on the Caimano they are on the right. See these pictures:
Here the Castoro:
Castoro.png


And here the Caimano:
Caimano.png


As you can see, apart the position of the valve which is opposite side, the two units have also a very different path for the gas: the Castoro is still employing the old scheme inherited from traditional Italian-style single-hose, pendular units: the gas goes forth and back through the soda lime canister, so the filter is fluxed both inside-out (while exhaling) and outside-in (while inhaling).
Instead the CAIMANO employs the Haas circuit, traditionally employed by Draeger units, where the soda lime canister is fluxed only once, in one way (on the exhaling path).
 

Angelo Farina

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Thanks for the doc. Indeed Sanosub P96 (P for Pendulum) and Castor P96 then Sanosub C96 and Castoro C96 pro... different companies, small mods, not much differences if only quality built as OMG seems to have a better reputation.
Angela, during your ARO training, which unit did you use?
I was trained using a pendular unit, the CRESSI mod. 57B:
Cressi%20Aro%2057B%20-%201.jpg

See here for more info:
CRESSI SUB Aro 57 B rebreather | BluTimeScubaHistory

Later on, my club (Parmasub) did buy a much modern unit, the Technisub New ARO:
TECHNISUB-Aro-ciclico-1973.jpg

see here for more info:
TECHNISUB Nuovo Aro - rebreather | BluTimeScubaHistory

This unit was very advanced; double hose with fully circular circuit, and TWO soda lime canisters, one on the exhaling path and one on the inhaling path. Automatic oxygen injection with an on-demand adjustable valve and manual bypass valve.
The back of the unit, staying against the chest, was transparent, so you can visually check the status of the soda lyme (it becomes blue when exhausted).
This unit was terribly expensive at the time (1980).
Later on, when i started working for SIEL (OMG) I was using the Caimano MK4 CDV. Here I am inside the test tank at OMG (near la Spezia) , in 2011, testing the Caimano MK4 with a number of hydrophones, for assessing the noise produced by this unit:
IMG-0974.jpg


Here the unit I was using:
617e961b.jpg
 

jale

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The automatic oxygen injection on the Caimano IV is standard on the pure-oxygen version, but has been removed in the "deep ARO diving" version he has got, as it is dangerous to have automatic oxygen injection when using the system below 6 meters...
As said, the telemonster's unit looks to me as the military-grade unit which was only sold to Italian Comsubin incursors, and which is not possible to buy by normal recreational divers.
The main evident difference between Castoro and Caimano units is that in the Castoro the tank's valve and injection hose are on the left, whilst on the Caimano they are on the right. See these pictures:
Here the Castoro:
View attachment 668513

And here the Caimano:
View attachment 668514

As you can see, apart the position of the valve with is opposite side, the two units have also a very different path for the gas: the Castoro is still employing the old scheme inherited from traditional Italian-style single-hose, pendular units: the gas goes forth and back through the soda lime canister, so the filter is fluxed both inside-out (while exhaling) and outside-in (while inhaling).
Instead the CAIMANO employs the Haas circuit, traditionally employed by Draeger units, where the soda lime canister is fluxed only once, in one way (on the exhaling path).
I am not too sure about the flow path as in fact you can choose it just by swapping the mushroom valves.
Yes pendulum units have the gas going forth and back (and that why the breathing must be different than when you use a circuit) but both Castoro and Caimano use a circuit.
Indeed, on the top of the canister you screw the cover in which the inhale and exhale hoses are connected and the gas goes from the exhale hose to the canister, then in the bag, then back to the inhale hose. The gas doesn't go twice in the canister like a pendulum. But by swapping the mushroom valves, you can decide if the gas goes first in the bag or first in the lime.
Here is a pic of the small all metal canister of my c96 unit. Looking at the canister, the holes on the outside take the gas out of the canister into the bag. The holes in circle in the center take the gas out through the canister. The center hole is to screw the cover and you can also see an o-ring isolating the two in-out takes.
So the differences between Castoro and Caimano must only be about usage and options, the Castoro being the base model.
About the left and right position of the valve, I don't think it is a difference as, this is also swappable: you have a port on each side of the bag. Maybe the militaries prefer to have them on the left for some operational purpose.
But I am jus an "amateur" and maybe I am all wrong.
IMG_20170930_115401.jpg
 

Angelo Farina

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Your unit is definitely a Castoro. However, I never used a Castoro, only the Caimano MK4. Which looks different to me. Indeed, it was 10 years ago, so my memory is not very fresh on some details of the unit.
On the Caimano I do not remember the possibility to mount the tank with the valve on the left...
 

jale

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Your unit is definitely a Castoro. However, I never used a Castoro, only the Caimano MK4. Which looks different to me. Indeed, it was 10 years ago, so my memory is not very fresh on some details of the unit.
On the Caimano I do not remember the possibility to mount the tank with the valve on the left...
Yes definitely a castoro but I got a Caimono bag!!! Go figure! Mismatch stuff found on the aftermarket surely :)
Anyway the most important thing is to have fun in safe way knowning what we are doing:thumb:
DSCF3291.JPG
 
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