Apeks DS4 alternatives for rebreathers

[Angelo Farina]

Some manual rebreathers leak O2 into the loop with constant mass flow. If the IP rises with depth, more O2 would be pushed through the orifice. But you just want one 'surface liter' of mass going into the loop whatever the depth is.

Thanks, now it is very clear...
The rebreathers I did use were either pure oxygen (ARO) or SCR fed with Nitrox, so in both cases there was not this issue.

 

[mr_v]

Has anyone tried HOG D2s?

 

[divingx]

He did a run for me. I just bought 5 to make it worthwhile

Do you have a stronger spring in your MK17s like the DS4s from Fathom?

 

[slimshady]

Correct me if I am wrong, but with a cmf or needle valve and blanked stage isn't the seat open all the time?

 

[Angelo Farina]

Some manual rebreathers leak O2 into the loop with constant mass flow. If the IP rises with depth, more O2 would be pushed through the orifice. But you just want one 'surface liter' of mass going into the loop whatever the depth is.

Found a proper extended explanation here:

Understanding Constant Mass Flow ADVANCED DIVER MAGAZINE By Paul Raymaekers

But, after reading it, I confirm my choice to stay away from this kind of rebreathers...

 

[JMBL]

Found a proper extended explanation here:

Understanding Constant Mass Flow ADVANCED DIVER MAGAZINE By Paul Raymaekers

But, after reading it, I confirm my choice to stay away from this kind of rebreathers...

Thank you for sharing the article, but can you explain your choice ? Just an honest question, not a way to open a can of worm or to start endless and fruitless rantings.

 

[Angelo Farina]

Thank you for sharing the article, but can you explain your choice ? Just an honest question, not a way to open a can of worm or to start endless and fruitless rantings.

We are going severely off topic.
During my first diving course, in 1975, I was trained with CC rebreathers as a simpler, cheaper alternative to air tanks. That was the ARO, a CC pure-oxygen rebreather widely employed for military applications (Navy Seals, etc.).
It was made famous in Hans Hass films in the fifties, and it was the standard diving equipment used for sport diving here in Italy until, say, 1965.
Using a CC rebreather means perfect buoyancy not affected by breathing. A light device (less than 10 kg) providing several hours of diving. A cheap device, costing half a tank with regs and BCD. A silent device (no bubble noise). A simple device, purely mechanical, no electronics, no complex valve system (oxygen was manually injected in the loop).
Max depth was limited (initially 18 meters, then progressively reduced due to oxygen toxicity studies, now it is just 6 meters).
When the depth was reduced, a variant was introduced, making the loop semi-closed, and feeding it continuosuly with a flow of Nitrox. This semi-closed version was slightly more bulky (the Nitrox tank had to be larger than the small 1-liter oxygen tank), but maintained all the good benefits of the ARO, whilst extending the max depth to approximately 30 meters (depending on the % of the Nitrox mixture used).
I loved both the ARO and the Nitrox SCR variant.
On the other side, CC rebreathers evolved in complex devices including electronics or mechanical systems which attempt to control the mixture, using both a diluent tank and a pure oxygen tank, and allowing to go much deeper. They need always a bailout system, so the diver must carry a very weighty and bulky equipment. You loose the main big advantages of the simple rebreathers I used...
And going deeper than 50m is not very appealing for me, although when young I made some stupid dives in air down to 60+ meters.
In conclusion, the evolution of these modern variable-mixture CC rebreathers resulted in them being more complex, more expensive and more weighty and bulky than an OC system. So they have lost all of the appeal originally found in rebreathers.
Of course they are the optimal choice for deep diving with helium mixtures (also due to the cost of helium).
But for recreational diving with Nitrogen-Oxygen mixtures to less than 50m, I really see no point for using those complex rebreathers.
I see some benefit using a device such as the Mares Horizon SCR, only problem is that it is quite expensive, whilst an ARO was really cheap at the time...

 

[rddvet]

Has anyone tried HOG D2s?

Even back in the days when Edd had them dirt cheap I had nothing but issues. 2 out of the box had ip creep and couldn’t be used without a service. Another one we had issues with but don’t remember what. Myself and 2 dive buddies bought about 7 of them all with issues.
My understanding is the price has gone up which makes them even worse.

 

[Capt Jim Wyatt]

I think a more IDEAL setup is a hybrid type unit.
One that has a CMF function and an ECCR function. I had a rEvo with a CMF valve for several years and it worked just fine.

 

[mr_v]

I think a more IDEAL setup is a hybrid type unit.
One that has a CMF function and an ECCR function. I had a rEvo with a CMF valve for several years and it worked just fine.

I concur. I like the rEvo CMF, but LOVED Fathom's needle valve.