Dolphin-Trimix

[Mikel-Deko]

Hi.
I'm planing a wreck dive in -50 mtrs. I've got a modifyed Dolphin, and i can breathe two gases in SCR. I'm thinking in Tx 28/30 thougth the 32% jet and O2 trought the 100% jet. Opening the O2 tank in -35 mtrs the Ppo2 will go up to 1.3 or so and, once in the -6 mtrs stop just close the tx tank clean the loop and 96% O2 for deco. Obiously with enough bail-out (2 x10).
Another posibility: Tx28/30 32%jet // Ean50 50%jet and O2 Open circuit.
What do you think out there?

[NotDeadYet]

I knew someone who did this before, can't recall which jets he used though. He said the flow characteristicschanged quite a lot by the addition of helium into the gas.

What is the flow rate of the O2 jet? If it was low enough then it is basically acting as a KISS valve.

I suppose another option is to connect the trimix ONLY to the bypass on the dosage head and oxygen to the O2 jet. As you descend then the bypass will inject trimix into the loop while the O2 jet adds oxygen continuously. What is the point of having a constant flow of trimix? All you need is for the bypass to add trimix enough to maintain loop volume and for the jet to add O2 just like the KISS.

There are a few points that I can see with either system:

I wouldn't dive it without some ppO2 monitoring. At least two cells, I don't think one is adequate for gambling my life on especially on a deco dive.

You need to know the O2 jet flow rate. If it is higher than your metabolic rate then the loop will become hyperoxic. Don't the Draeger jets tend to be quite high?

You have no manual O2 addition. If the ppO2 in the loop starts to drop then there isn't much you can do to maintain it except lots of flushes. I'd imagine this would make deco planning a bit of a nightmare too.

Personally, my own view would be too just add ppO2 monitors and a KISS valve, the Draegers are perfect for it. Like this guy www.tmishop.com

I suppose it's one of those things that you can't find out about until you try it. Do tell us how you get on.

Best of luck and take care,

Stuart

[Mikel-Deko]

Thank you for the answer.
Yes, I've got two o2 sensor in a Oxy2. The flow of a 100% O2jet from Draeger is 1.5 litres/min. !!too hight !!! That was my first idea, Kiss system with this jet, but...
About the flow, i've been told that, with trimix, the flow doesn't change to much. Also he said that with Heliox the flow change a lot...
I'will take care, thank you...

[NotDeadYet]

Shame the jet is too high, it would have worked quite well. Maybe this is why they make jet with a high flow rate so that divers cannot use it as a KISS valve.

Good luck and tell us how it goes.

[narked at 90]

i know of one man who runs mix in scr mode but i dont think it's worth the hasel to make a good reliable system for deep and shallow much beter to just close the loop, the pool jet is far to high with out turning down your Ip which then makes the other jets pretty much useless and you still have the problem of no manual add for o2.
i ran my dolphin ccr on mix this weekend 20/40 but had the ADV pack up on me which made breathing rather hard!:-)
good luck and let us know what you decide on.
best regards john routley