O2 addition methods

jmurba

I understand your point of view and respect it.
I personaly think that everything can be bettered or at least adapted to the personal requirement of a given diver.
also again paul and gordon have been home builders before building machines for others.
paul modified dolphins and ida's before designing his rebreather
I know quite a few revo diver who dive modified revo.
it does not means that draeger or paul did a bad job but simply that their rebreather has been designed for a standard diver and that non standar divers felt like adapting those re-breather to thier needs .

what I don't agree with is coming on a homebuilder section of the forum to say to a potential home builder, don't do it yourself , take a stock unit and dive it !

I could at least understand it if you are a home builder doubting of the capacities of doing a good job.

but are you a home builder ?

if you are not a home builder and if you have no certitude about this guy technical capacities I don't understand you advice him not to go on with his projet.

it is just my opinion .

as a home builder I try to share my experience with other home builders or future home builders.

this is the goal of such a forum.

respectfully yours
jean mi

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Packhorse

Because the solinoid of a eCCR requires a depth compensating regulator. The pressure diffrence from the IP to ambiant pressure will always be 7.5 bar (for the inspo apparently)
With a bigger CMF orriface you will simply get more O2 flow at deep depths when using a depth compensating reg as the IP will be rising.

If you use a non compensating reg then the CMF oriface will cease to work as a CMF (Constant Mass Flow) when the water pressure reaches over 50% of the IP pressure ie 27.5 meters(3.75bar). And less O2 will flow the deeper you go. Also the solinoid will start flowing less and will have to activate more to make up for its lower flow rate and the CMFs lower flow rate. It will also stop flowing completely when you get to a depth of 65 meters (7.5 bar).

So you cant have it both ways with 1 1st stage.

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Packhorse

I agree Jmurba.

Lots of silly ideas and questions are thrown around by those new to something. I should know I am new to RBs and moding them so have had some strange ideas. Some that turned out just plain stupid and some others that I later found out others have implemented very successfully.

Forums like this shouldnt be used to put people off modding but for steering them in the right direction.

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divelermentov

because it is not about getting a bigger gas flow,
the issue is to keep the orifice at sonic speed so you get a constant gas flow.

The orifice will only stay sonic if the upstream pressure is roughly 2.2 times the ambient pressure, therefore 7 bar will limit you to somehow 30 meters.

If you are happy with such a depth limitation, fine, however most of us aren't.

secondly as you decent the ip stays cosntant, means the pressure differential is reduced, so your solenoide hasn't got a working pressure of 7 bar, but 7 bar minus x (depth), i do not know how much this will impair the gas flow thru your solenoid ?

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divelermentov

well said jean

i totally agree, stock units can be modified, and will be modified due to various reasons.

However I dont think it is a particular clever idea to buy one stock unit (e.g. inspo or optima) only to modifie it straight away into something which looks like a rEvo.
If I had to buy a Rebreather now and did live in europe, i would give paul a call and pick up a hybrid rEvo form him.

However I do have an inspo, and I am happy without,
minus that it comes without HUD ( I do have an older classic), and minus that it is not a hybrid.

When I bought the unit some of these options were not available.
Agreeable I could flick it of possibly get NZ$7000, but by buying a new one would have to pay at least $NZ18000 plus training, plus getting to teh training etc.
therefore modifing the unit by means of homebuilding can be a very valid option.
However saying that i will still use the help of professionals to do some of teh jobs. John (narked@90) has a great design and engeneering service,
the same with Martin (Tecme). Yes parts appear expensive on the first sight, but all that stuff is custom build to a fanstastic standard, and at the end still much cheaper than flicking teh unit off and buying new.

E.g. to mod the inspo into a hybrid will cost me aprox $NZ1200, HUD $NZ1500, having to run 6 cells - well 450 per year in extra.

If i compare that to $NZ10.000 in upgrade costs, that is something like 15years to get to teh same cost.

On another note, if you homebuild something it becomes your baby - this can be very satisfying. For example I had my unit with teh new HUD in the pool yesterday and it performed floorless.
Ok only a short dive but still makes you feel good.
Yes spend several weeks working on the thing to get it to work as i wanted, did course quite a bit as had some shorting in the connectors, but hey sorted it out. Had to mod the DSV attachment as well, but now great to read even in strong backlight.

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Janwillem Bech

check this:

MCCR in Depth
Gas flow through an orifice

JW

seeboth

wow this thread has gotten away from my original intent,

I guess I should have just asked if any body has knowledge with making a addition block such as the one used in the Pelagian.

I am still just going through the concept phase right now, and trying to figure out how I would make the mods I want to, Im not planning to toss this on a unit and start using it without testing. I think of the stock unit i plan on modifying as a bench mark against what I can judge my modifications against. I think of it as a way of controlling variables: If I know the unit works well as is I can change it to back mounted counterlungs, see if all is good then I can see if the hybrid system works, then I can see if any other changes work etc...

But right now I am trying to do the cad for a needle valve, like the one on the pelagian that i could easily check the flow rate and lock down for the max depth of what ever dive.

What I am trying to figure out is what parts are used to make this block, I know it is a Swagelok part and i know it is just the valve out of the Swagelok assembly I am just not sure what needle valve it is.

I am also trying to figure out what part is used for the bypass valve.

If any one has has experience making a block like this that would be great,

thanks

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OceanOpportunity

I'm using an Aalborg needle valve with a cV of 0.0005 with a standard out of the box piston first stage. Works exceedingly well. manual add is with Clippards modified to include stainless rather than stock springs.

I can help you source and/or supply parts if necessary

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jmurba

Hi my friend,
In addition sorting out your problems you know weack points of the system and the good strategy to keep them away.
regards
jean mi

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jmurba

my first kiss dives attempts were done on the same orifice then the first gordon smith orifice, the IP for 0.8 lt/minute was 7 bars !!!

I dived it down to 50m without a shadow of a problem,

of course due to the fact that the orifice was not sonic anymore I had to face a flow rate cut but ok It still worked fine.

like gordon was saying "for the time one spend in 60m even a dil flush would be enough to maintain the ppo2 level"

what I mean is that the dogma of the sonic flow is too limiting.

if you read the jacques vettier book about rebreathers you will find out tests and charts showing that getting a sonic flow is nice but that the flow rate drop is not so dramatic when you get a bit under the 2.00 ratio.

the sonic depth is not an absolute limit under wich you will not have o2 anymore, it is more subtile then that, it can be exceeded.

personly I use an hydrogom with 11 bars for 0.8 lt/mn and dive it down to 65-70 m and I have never noticed any need for injecting manualy more often.

last thing, swagelock website provides a flow rate simulator where one can tests all of that, orifices and needlevalve have different reactions

regards

jean mi

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