Drager Jets

[Odin]

Thats what I used to do..
plus an 80% in a second 60% jet for accelerated deco!

[froglee]

I dived the Dolphin a couple of times down to 40m using the 32 jet and the 5l 32NX mix and there is really not much difference from my 15l open circuit time wise...about 40 minutes leaving the 50bar reserve.As Freeflow says its not a very useful nozzle if you are diving by the book so for deeper diving with the Dolphin I guess you got to learn the mixed mix/nozzle system to get the time benefits.I can just about squeeze 2 acceptable dives with my OC buddies with the 40NX mix and the 5l without a refill or a decant....most of my clubs diving is no deeper than 30m.50Nx gives a more comfortable double dive with a 22m depth limitation but is ideal for 20m stuff like Capernwray.60Nx I have only used a couple of times spending hours taking photos bimbling in the shallow waters round Porthkerris.Its good for pool training as well!Of course the instructors get to use the 02 jet.....Wonder what that's like?
One nice thing of course is that two divers [who might have very different OC air consumption] use virtually the same amount of gas with rebreathers so dive times are a bit more predictable.

[Neil McLeod]

The 32% jet is a waste of good nitrox. If you have a pO2 meter you can work out your vO2 [Oxygen consumption] and then tune your cylinder gas to a slower flowing jet, I use 40% through the 60% jet to get maximum extention [down Amy-Ward], although this will lean the mix I breathe to 30% under a heavy workload.

Freeflow must have a lower VO2 than me. I end up with 28% in the loop if I put 40% through a 50% jet. Now going MCCR.

Neil

[Freeflow]

Hi Neil,

From your figures it looks like your vO2 is 1.22 l/min. At 1.22 you could run 45% through the 60% jet for a loop of 30%. 50% through the same jet would get you a 37% loop.

This is of course if you could guarentee that your vO2 never changes!

If you were to do a dive to 30m looking for an ideal pO2 of 1.2, and assuming that you had a high and low vO2 of 1.6 and 1.1 45% on the tank should do you nicely [although you still need a pO2 gauge]. At the high workload you would get a loop of just over 21%.

Do you have my spreadsheets and tables for Dolphin gas and jet matching? If not send me an email [not a PM] and I'll send them to you.

My vO2 is generally in the 0.8-0.9 region, with a working peak of 1.2. I tend to take at least five readings of pO2 vs depth every dive,and periodically do an exercise check to verify the figures. I dive the Dolphin conservatively and a hyperoxic rather than hypoxic loop is normally my problem.

For the same dive as quoted above I would be able to use 40% through the 60% jet.

Have a look at Semi Closed Rebreather diving gas calculations. if you haven't already, this runs through the formulae for the gas matching, and if you have any further questions just ask!

[Neil McLeod]

Hi Neil,

From your figures it looks like your vO2 is 1.22 l/min. At 1.22 you could run 45% through the 60% jet for a loop of 30%. 50% through the same jet would get you a 37% loop.

Thats right, my VO2 is generally about 1.22 and that is when just pootling about. Have nearly doubled this when I annoyed an Angel shark by mistake. (it was buried in the sand like a ray).

I do have an Excel sheet set up for these calcs, but usually use a set of calcs on a palm. These also do the partial pressure blending calcs for me.

I am in the process of closing the loop on one of my Dolphins, with parts from Tecme. I intend to set it fairly lean (0.8 - 0.9 lpm) and do a fair amount of injecting as I can add O2 easier than I can lose it.- shut off O2 or vent and flush loop with dilutant. Like you, more worried about hyperoxic rather than hypoxic loop mix.

Neil