NewB: SCC computer

[igoRluse]

Hi all,

I am seriously considering purchasing a Dräger Ray to get my foot into the rebreather community and through all the reading and research I have done, have figured out a lot of the questions I had about rebreather diving. One question that remains unanswered though is the use of computers with SCC rebreathers.

By what I have understood, correct me if I am wrong, when using a SCC with eanx you would have the same nitrogen absorption as using the eanx in open circuit. From there I imagine, you would simply use a ntirox capable computer...

Am I correct?

 

[landfish]

correct
you figure out your motablizim rate and find out what the bag breathing gas is and you then set the computer to that number and dive
i think you would be better off with the dolphin then the ray

 

[landfish]

allways dive wiht a ppo2 meter so you know exactly what you are breathing

 

[caveseeker7]

By what I have understood, correct me if I am wrong, when using a SCC with eanx you would have the same nitrogen absorption as using the eanx in open circuit. From there I imagine, you would simply use a ntirox capable computer...
Am I correct?

Not quite. When you dive OC you breath the fixed percentage of O2 in you mix. So you set your nitrox computer to that mix, and it will calculate accordingly.

When diving a rebreather the mix within the loop changes. Even with a SCR that uses pre-mixed gas. You metabolize gas that is in the loop, and that amount will vary depending on a variety of factors like you physical condition, your workload etc.. In a cmf-SCR like the Ray gas is added continiously through the metered orifice, and the bypass as needed. They can be 'overbreathed', meaning you metabolize more O2 than is added. Which is why I second landfish's statement that you should should dive with pO2 monitor.

Now in regards to the deco computer, if you use a computer (or OC tables) you have to calculate the worst case scenario. To figure out the O2 toxieties you use the highest O2 content (mix in tank), for deco the highest N2 content (when you 'breath down' the O2 level considerably and thus end up with a higher N2). This will give you safety, but obviously will be very conservative as you can't really take advantage of the actual mix in the loop.

If you add a pO2 monitor such as Dräger's Oxygauge, you will be able to watch your loop content, take notes and program your fO2 computer accordingly (though you still need to be conservative). You will also have the added benefit of high (depth) and low (overbreathing) alarms.

I think the better alternative is to use an O2 cell integrated computer that measures the O2 contend, displays it, and uses it to calculate your deco on the fly. The Ray's P-connector that allows you to install the Oxygauge will also accept the cell holder for the DeltaP VR2, a nitrox computer with 4 mixes OC, semi-closed or closed circuit. (As well as the VR3 and HS Explorer, two cell integrated 10 gas trimix computers, though they are overkill for a Ray).

Another possibility is the use of Uwatec's ZO2 computer with its Oxy2 SCR interface. The Oxy2 has two redundant O2 cells and screws between the rebreather and the inhalation hose. For the Ray you need an adapter as it was designed for use with the Dolphin. The pO2 is transmitted wireless to the ZO2 wrist computer. The ZO2 displays both your pO2 and the derived fO2, and uses the actual mix in the loop for its calculations and alarms. The ZO2 can also be used as a single mix OC nitrox computer, with or without wireless contents display.

 

[gkndivebum]

[...] Another possibility is the use of Uwatec's ZO2 computer with its Oxy2 SCR interface. [...] For the Ray you need an adapter as it was designed for use with the Dolphin. [...]

[Nice summary Stephan ...]

You can get the Oxy2 adapters for the Ray here

 

[wazza]

Hi all,

I am seriously considering purchasing a Dräger Ray to get my foot into the rebreather community

The production of the Ray had been discontinued in January 2003.why buy a Ray?

 

[nitrojunkie]

A KISS rebreather is priced more like a Dolphin (except it come with multiple PO2 monitors) but is a CCR system that will give you much better ppo2 levels and is easier to use. Much safer in my opinion. I have only pool dived the KISS systems but they are well built and designed by Gordon Smith who is ramping up rather than ramping down the line.

The only catch is that you will need to get pure o2 rather than Nitrox to dive the KISS but it's not that big of a deal depending upon where your travels take you.

They are soon to be releasing a Sport KISS, cheaper/lighter/smaller which might also be a great way to go. http://www.jetsam.ca will link you to the KISS site.

 

[steevke]

A KISS rebreather is priced more like a Dolphin (except it come with multiple PO2 monitors) but is a CCR system that will give you much better ppo2 levels and is easier to use.

A KISS is a cheap rebreather if you're located in the US/Canada. If you live in Europe, a KISS is much more expensive than a Dolphin.

A Kiss is 4600$, to which you need to add tanks (400$) + wing system (400$) + O2 cells (210$). Add shipping costs (about 150$), VAT (between 16 and 21%) and import duties (4%), and the 'cheap' Kiss now carries a price label well above 6500$ :eek5:.

Still cheaper than a Meg or an Inspiration, but much more expensive than a Dolphin (which can be bought new for under 3000$ in Europe).

Steven

 

[Diver Mike]

I would not let the price be the guiding fator in chosing life support equipment.

Decide what type diving you will be doing with the RB and purchse the appropriate one for your intended usage.

For more information onthe KISS and Sport KISS see the other threads in this forum.

 

[caveseeker7]

Ya'll know that Perth is on the west coast of Australia, right?

Judging by Paul's post on the Oz board he's pretty set in his decission to purchase a Ray. Also, I'm not so sure if there is much of an instructor base in that area for most CCRs.

Paul, the only Jetsam KISS I'm aware of belongs to Steve.
Steve's KISS page has a pretty good teardown, and he'll answer any questions you might have.

The KISS is not a bad idea, really, it also has a cmf orifice. Unlike SCRs, the flow rate is just below your metabolism, and you top it off manually by adding O2 with the valve. It also comes with an OC integrated DSV which is great.
Worth looking at even if you have to save a while longer.
And for more recreational profiles Jetsam will introduce the Sport KISS next month at DEMA, which is smaller, lighter, and pricewise probably around the list of a Dolphin.