Blanking number 2

nicka

Can anybody share with me their experiences or opinions in say...blanking off the second oriface in either the 40%,50% or 60% and using a "manual add" to suppliment the ppo2 when needed .
I know that some things are best left unposted,but I have some questions I cant get my head around.
Thanks for any help.

Freef

You're more or less running either a SCR O2 rebreather or a mCCR convrsion if you do that. By second orifice I assume that you mean the whole thing and not one of the two jets inside the metered flow valve itself.

The Drager first stage will increase the IP until the ADV operates unless it is connected to a continual flow, so yo would still get atrickle of gas added to the loop.

If you intend to run a second bottle that will supply the loop [mCCR] John [Narked at 90], Brent [Dive the World] and others on here have run a similar system, try doing a search on Dolphin CCR conversions.

If you are looking at running an O2 rebreather you will be limited to 6m.

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David.

Currently owner of two differently sized ankles.

nicka

Thanks David
Im curious about blanking the second oriface within the dosage jet itself,as a different approach than say using 40% on the 60% jet?, which still allows use of 40,50 or 60% gas but at less flow.The fo2 math still works unless working harder .Anyone done this?

Freef

You won't have any luck blanking one of the holes, for a start they are very small [laser drilled ruby I think] and the design is such that if one blocks the other will be able to compensate for that by raising the flow rate.

I use 40% through the 60% jet [loop fO2 of 28% at a vO2 of 1].

This post:

http://www.rebreatherworld.com/semi-...g-4-parts.html

details the maths and procedures for changing the flowrates and gasses, and the dangers of doing so. It depends on what you are trying to do with the Rebreather as to the best way of proceeding. If you are looking at keeping the unit loop standard and want more duration then using the 60% jet will help, or using a 10L tank. You will still be restricted to 2-3 hours [scrubber duration] and 40m though.

For going deeper you will need to look at making the unit closed, I think everyone who has done this has gone mCCR. Some have dived trimix in the unit, and I am doing some thought experiments along this line at the moment, but I think the risks will outweigh the benefits.

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David.

Currently owner of two differently sized ankles.

Mikel-Deko

Hi.
I was using a 60% dosage with 100% O2.
In the way up, say at -12 mtrs, i used to open the O2 tank. This way, the ppO2 in the mix was increasing. I had always the posiblity of washing the loop in case that the mix was to hight ppO2.
Hope that help you.
Regards
Mikel

divetheworld

Two things, are you still going to be SCR? In which case dont bother with a manual add, just exhale through your nose and fire the ADV.
Otherwise your better off going KISS, I will explain in more detail if this is the case.

Secondly, you can remove one of the jets from the dosage unit by unscrewing it, then you can drop in a grub screw with a sealing gasket, however... The reason for the two jets is that if one should block, the user will still have a (arbeit lesser) supply of gas entering the breathing loop to slow or limit the possibility of a fatal failure.
This is one of the design parts of the Dolphin that made it so good as a SCR.

Brent

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nicka

thanks everyone, my unit is being slowly pushed towards a kiss unit ,
It has 2 cell monitering, manual o2 injection and a dil port that blows across cells.with 2x 3.8 ltr bottles
1x nitrox and 1x bailout/dil.
Still running drager reg,and jets.
Im just looking for an intermediate stage between the two ..standard scr and kiss ccr.

Gregv

C'mon Nick - just close the thing up and get on with it. Come and grab the bits you need from the parts bin in the garage. First up, get rid of the Dolphin 1st stage, it only causes problems on a KISS style unit. I've got a first stage you can borrow and blank off to run a KISS style orifice until you buy your own DS4 and blanking plug...

Trying to do it as you describe probably isn't going to provide any significant advantage over what you can do using different nitrox mixes through the standard dolphin jets.

Close it up and we'll get out and do some decent dives out at the Knights!

Greg

divetheworld

Admirible.
If you wish to have an intermediate, then I cant think of a better way than Mikel suggested. Carry a small (1-2ltr) ally tank filled with pure O2 and connect it directly to a 60% orafice, maybe with a tee into the ADV depending on your experience level. When you get to your deco stop simply shut down your main gas and switch on the O2, do a flush and enjoy accelorated deco. All the parts are available at Tecme link -> http://www.tecme.de/frame_eq1.htm
Things to watch are your PO2 because a 1-2ltr tank will only last so long and make sure it is isolated when on the depth phase of yoru dive for obvoius reasons.
This makes a nice simple extended range rig without too many tanks. you still need bail out blah, blah blah.
Or..
You could mount one 3ltr on each side, one O2 and one bail and set it up this way. Ten seconds later you can whip off the gas hardware and change it to CCR....

Link -> http://www.therebreathersite.nl/06_Homebuilders/brents_dolphin.htm

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Freef

2 cells is a bit of an odd setup for CCR or an SCR/CCR hybrid that relies on pO2 monitoring for control of the fO2 in the loop.

On the standard Drager SCR the pO2 meter is passive and does not control the addition of O2. The Submatix CCR model uses two O2 cells and displays [they are set up in the way that the Drager Oxygauge].

The downside is that if one cell is on the way out you don't know your pO2. With three cells and displays then the likelyhood of two O2 cells experiencing the same failure mode at the same time are remote, so it is safe to abort the dive using the two figures that agree and ignoring the one that is out.

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David.

Currently owner of two differently sized ankles.