O2 addition methods

seeboth

I recently decided that i have way to much to learn about rebreathers to start from scratch, so im looking at starting with a stock unit and then extensively modify it untill i make my own unit.

Essentially i want to convert a over the shoulder counter lung eccr into having back mounted counter lungs. Since i would most likely want to fly the unit manually with a low set point on the controller, and i need manual addition blocks anyways, I want to make the unit a sort of hybrid system.

As far as o2 goes i want to make needle valve assembly, like the Pelagian, with the needle and the bypass all in the one block. And I want to make an orifice block, where the orifice would be right in the block with a bypass valve. The orifice would be fed by a depth compensating first stage, just like the needle valve. That ways all i would have to do is switch the blocks to change which style of o2 add the unit has so i can figure out which i like best.

I would most likely start with the needle valve block since if i lock it in place it is essentially an orifice. Does any one have experience in making something like this. Ive seen them on rebreather world before. what is the product number for the swagelock needle valve used? and where is the manual inject part from, is it just a clipper valve from mcmaster carr?

Thanks,
Al

I should add that the solenoid would be fed from another hose form the on board o2 1st stage. The block would be connected to the on board 02 with w/ quick connect that i could switch to off board o2, that way only the solenoid would use the on board o2.

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yes those are double lp steel 121's on my back
yes those are the main reason i want a rebreather

divelermentov

i am looking to do something similar to my inspo

you might want to talk to Martin at tecme ( Tauchen - Cave, Nitrox, Rebreather Ausbildung, Tec Ausrüstung, Reisen), they do a nice looking CMV.

just one remark, if you use a depth compensating first stage the o2 flow thru the orifice will increase with depth, therefore depth limiting you severely before you get too much flow and have to shut it down. Therefore as far as I know you will have to use a non-depth compensation ( constant ip) 1 st stage.

Talk to John (narked@90) as well, he is a good guy with fantastic advise.

But these are only my .02

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seeboth

I think since I am not diving trimix with a rebreather yet, i am thinking of trying to tune the orifice, or needle valve to deliver something just under my metabolic o2 consumption at, what would probable be my max depth of about 180 ft. So it wont deliver as much o2 as I ascend, and add more as I get to my bottom depth. Then when I start going deeper I would simply adjust for my new max depth.

Thats why I think I am going towards the needle valve, since it would just be a matter of measuring the flow rate on the surface and then calculating what it would be at my max depth, then I would lock it in place and just add manually more often while I am shallower.

Still the unit will be a hybrid so if I miss an add the solenoid would kick in before the O2 drops too much.
well thats in theory...

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yes those are double lp steel 121's on my back
yes those are the main reason i want a rebreather

Packhorse

It would seem to me that the simplest solution is a CMF style of O2 addition using a non compensating 1st stage. Either using something like the KISS valve system or the Tecme system or even something along the lines of this.

If you are staying above 160ft (60 odd meters) then a 1st stage fixed at 13 bar absolute (max for a apeks I believe) should work fine.

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paulraymaekers

are you sure you will end up with a better unit then the stock unit?

paul

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nobody

Why not have the needle valve seperate from the manual add? This would make it possible to have 2 orifices, once you start getting deeper you isolate one and turn on the other extending the range of the unit.

seeboth

To be honest... no, I am not sure...

But I know I love to tinker with things, and currently I havent really found a stock unit that I think is the right solution for me. Which, I think, is why most of the people that are read the home build forum do.

Dont get me wrong there are plenty of great units out there, I just think they each could use some changing (granted this is in my novice opinion). I'm sure you thought the same when you decided to build the revo. My plan is to start with a stock unit and make the changes I feel are needed as I get to them.

My original thought is to start with and optima, I really like the HH electronics, and HUD, and I think it could be converted to back mounted counter lungs pretty easily by making a new backplate that would raise the unit enough to have the CLs in between your back and the unit. Plus, the dive shop I work at is a Dive Rite dealer, so the optima would probably be the easiest unit to get and the $$ isnt bad for a eccr.

Im sure a fixed IP first stage would be easiest, and maybe best, but I guess I am still hesitant to block a first stage, Id rather be able to use all the same first stages on my rig, besides the whole idea is to just make the solenoid fire less that it would in full eccr, so either I add manually more often or I use this leaky valve system of some sort to help prolong the time in between when the solenoid fires.

Im still pretty new to ccr though, so correct me if im going way off course,
thanks, Alex

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yes those are double lp steel 121's on my back
yes those are the main reason i want a rebreather

jkaterenchuk

You might not know that there are some Kiss Classic units retrofitted with the HH electonics. That would seem to fit your menu of requirements. I am not an expert on them but a quick search would probably turn up whom the current user are.

John

mountain diver

It would seem to me, that you are inviting a lot of work if you want to change
the optima into what you are looking for.If you want a hybrid design, one with
backmounted counter lungs and full electronic control as well as manual,
why not pick up a Revo or a HammerHead rebreather? And add the needle valve yourself, if that is what you want to do. would seem the easier to me.








all the best.

divelermentov

Sorry mate you are well off course here,
do not dive a mccr with a depth compensating stage !!!!! This does only work for a scr NOT mCCR.
As your upstream pressure increase your o2 output increases as well which will make your loop hyperoxic at depth. THIS IS VERY DANGEROUS. If you than have only one first stage the only thing you can do is turn the supply off and drive the unit home by using the tank valve - not an easy task.

You either use one 1st stage non-depth-compensated as does the rEvo II hybrid. Howver you have to change the systems to eCCR only if you plan to go deeper than i think 80 meters ( Paul correct me if i am wrong).

Another way is to use 2 o2 tanks with 2 1st stages, one feeding the mCCR and one feeding the eCCR.

Good thing here is that a)you dont have to worry so much about the max depth of the mCCR,
b) you can run the mCCR at an ideal IP as well as you can run the ideal IP for the eCCR ( e.g. Inspo wants 7-8 bar ip for the solenoide, mCCr want 10-13 bar)

bad with that is that you will have a) offboard o2 which will make the unit larger - might be a squeeze in some wrecks afterwards
b) you have to maintain 2 1st stages

good thing - if you had an idsependent monitoring such as diamond HUD (www.rebreathersolutions.com - I think-), rEvo dream ( Paul ) or the shearwater HUD, your systems becomes double redundant. If you even throw extra o2 cells in your are redundant except for your scrubber.

good people to talk to are ( in no particular order :-) )
a) John - narked@90
b) martin - tecme.de
c) Paul - he does the rEvo - dont know the website by heart - check the net or PM him he is on this forum as well


but these are only my .02

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