Why is using the 32% nozzle on the dolphin bad?

[scubanimal]

Another newbie question. I was told today that its not wise to use the 32% valve on the Dolphin, instead it was suggested that I use 40%, limit myself to 100 fsw, and work up to the limit of 1.6 atm. As 32% is readly available, seems to give a better P02, allows you to dive recreational depths, I would really like to understand the rationale behind it. Does anyone help me understand this?

 

[carlislere]

I have no idea. I have used the 32% nozzle many times with my 50 cu ft tank without any issues at all. I have been to 110 feet with the unit using 32%. I have probably made half of my 100 + dives on the unit with 32%. However, with the 28cu ft tank at 32% you will have about a 35-40 minute dive. Go ahead and use the nozzle

 

[wedivebc]

Another newbie question. I was told today that its not wise to use the 32% valve on the Dolphin, instead it was suggested that I use 40%, limit myself to 100 fsw, and work up to the limit of 1.6 atm. As 32% is readly available, seems to give a better P02, allows you to dive recreational depths, I would really like to understand the rationale behind it. Does anyone help me understand this?

Are you monitoring the PO2 in your loop? If you do you will find the PO2 never reaches the mix in your tank. Because you are always inspiring (consuming) some of the O2 I would have no hesitation about going to the max MOD of your gas. I would say 100ft is quite safe on 40%. I would not ever exceed a depth that could possible result in a PO2 of 1.6. The reality is though it will not likely exceeed 1.4 even if you had a really relaxing dive.

 

[scubanimal]

I have no idea. I have used the 32% nozzle many times with my 50 cu ft tank without any issues at all. I have been to 110 feet with the unit using 32%. I have probably made half of my 100 + dives on the unit with 32%. However, with the 28cu ft tank at 32% you will have about a 35-40 minute dive. Go ahead and use the nozzle

How did you get a 50 ft2 tank to work with unit? Since I'm above avg size that sounds quite useful. So you don't see any hypoxia issues with that setting and depth? That seemed to be the issue, vice hyperoxia. - Thank you!

 

[caveseeker7]

Dräger at least used to sell a 50cu.ft. complete with their tank valve ($$$) for use with the Ray when equiped for 32% mix. Another, less expensive alternative, are the adapters available from Oxycheq (currently moving from CA to FL) or TecMe (in Germany - they have piles of adapters for most any project but are a bit more expensive than Oxycheq). They work well with rental tanks, too, when travelling.

As for the 32% orifice, it's used by plenty of divers. But as Ron pointed out, at a flowrate of 15.5 ltr/min. the stock tank just won't last long. The Dolphin's design just isn't very efficient at that depth.

 

[wedivebc]

How did you get a 50 ft2 tank to work with unit? Since I'm above avg size that sounds quite useful. So you don't see any hypoxia issues with that setting and depth? That seemed to be the issue, vice hyperoxia. - Thank you!

Hypoxia is only an issue with that orifice on the shallower part of the dive. Just remember to flush the loop at your safety stop and again before ascending and avoid heavy swimming at the surface.

 

[carlislere]

I bought an 50 cu ft tank, then ordered a Drager valve for the tank. I have used it for 32%, 40% and one time 50%. The 50% was in some springs to the south of here and had two nice 55 minute dives to 25 foot max. I do have to add some extra weight cause the tank is aluminum. I would love to find a steel 50 or 45 that is short like the 50.

 

[kennethw]

Real dump question, please.....How do you mount your 50 cu ft bottles?

A 50 cu ft is pretty big, so placing it where you would place the existing bottle holder at the bottom of the shell makes the tank protrude out the sides way too much. Placing it on the side of the shell (like the bail out) is possible, but the bottle is heavy and I am afraid the plastic cannot take the weight and the whole rig will be unbalanced (unless you use a 50 cu ft as your bail out too).

I've tried placing the bottle like a stage, but don't like that because in an emergency, it may be difficult to remove the unit to, say, remove entanglements.

I've built a frame for my Dolphin with tank mounts on either side, where I'm using 30 cu ft bottles for O2 and Diluent when diving it CCR.

Otherwise, I have a 5L Drager bottle which is OK.

 

[caveseeker7]

Simple answer, they'll stick out.
Just how far depends on the size of the tank,
I've seen divers use steel 63 and 72, and with an alu 80.

For sidemounts and really heavy tanks a metal frame inside
the shell should work, jdz in Oz even makes alu shells.

 

[Camerone]

I just mount the 50 cf bottle on the bottom in place of the standard 28 when I use one, which is fairly often, actually. The only difficulties are that the strap velcro isn't long enough (no big deal), and the hoses stretch to their limits when feeding the dosage unit.

I use a 19 cf bailout, mounted so that the bottom of the bottle just sits above the 50 cf on one side. The other side of the unit has a small argon bottle (6cf) to keep me warm in the drysuit. The 50 cf doesn't really stick out any farther than the edges of the two side-mounted bottles.

The Drager shell is really flimsy... for each of the mounts that I used, I fashioned a backing plate for the inside of the shell that helps distribute the forces across a larger area of the plastic. I watched quite a few Dolphins come into my LDS for service that had large fractures down the sides from people who mounted bottles without reinforcing the mount point one way or another.

FWIW, a small metal plate works wonders and can be quite thin. Personally, I just happened to have scrap quarter-inch thick ABS plastic lying around at work, so I cut two plates out with a laser and used them as backing for the mounts. It doesn't take much, but you have to do something or you will crack sooner or later.