Diving the Dolphin

GaryB · 17th July 2008, 19:42

I purchased a used Dolphin, had it serviced, secured a valve and tank, an Oxy2 and AirZ O2 computer, new O2 sensors, sorb, and am getting ready to dive it.

I took the PADI Speciality course in January of 2006, and have been studying all the material I received, as well as other materil I've obtianed from Rebreather World, and feel or rather felt confident about jumping in the pool with it before taking it into open water.

This portion of diving a rebreather wasn't covered in class...
I ran through the Dolphin Profiler xls spreadsheet, and was alarmed to see that at 12 feet with a 40% O2 mix and the 40% jet, there was insufficient inspired O2. (Thanks firemandiver for pointing this out to me!!!)

The profiler indicates a minimum depth of 50 feet to get the inspired O2 to 21%.

This got me to thinking about a bunch of different things:
1) I need to take a rebreather refresher class!
2) how can one make a safety stop at 15 feet with the rebreather in this configuration?
3) how does one make dives shallower than 50 feet with this configuration?
4) I'm obviously missing something; see item #1

I'm hoping a rebreather refresher class will shed some light on the topic, and hoping the experience an knowledge of Rebreather World readers will help as well!

Thanks!
Gary

GaryB · 17th July 2008, 19:47

Not sure why the pic of the spreadsheet didn't take the first time:

**Dave1w** · 18th July 2008, 01:00

Are you sure?

With my calcs, with an O2 consumption of 2.5 litres a minute, and 40% flowing at about 10 litres a minute, you will have at least 20% in the bag. I may be wrong, but I don't think so.

You shouldn't really be able to get up to 2.5 litres of oxygen a minute, but as I understand it, Drager designed the flow for all their orifices on the dolphin to give you 20% minimum at 2.5 litres a minute of oxygen consumption.

Try doing the calculation by hand with the formula in the book.

Dave

PaulTG2 · 18th July 2008, 03:23

Hello,

I come up with 21.7% O2. I don't know what the spreadsheet uses to come up with less than 10%.

(O2 injected - O2 used)/N2 injected =FiO2

((0.40*10.7)-2.5)/(10.5-2.5)=.217 or 21.7% FiO2.

That's injection EAN40% at 10.7lpm with an O2 consumption of 2.5lpm -- which is a consumption beyond what you'll sustain.

Can you show the formula the spreadsheet is using?

Sincerely,

-p

sailor · 18th July 2008, 08:54

Hi, there's something wrong with that sheet.
There's a lot of safety margin in Draeger's calculation.
Most SCR-divers i know use one jet-size smaller then required by the used gas.
According to the Draeger manual you'll never have below 20% O2 in the loop with 2,5 Ltr./min O2-usage.
Nobody can use 2,5 liter O2 per minute for more than a couple of minutes because this will cause real extreme exhaustion.
With your monitoring you are on the safe side anyway.
When you flush your loop before ascending you are on the safe side for sure.

GaryB · 18th July 2008, 14:35

I found this spreadsheet somewhere on Rebreather World. Unfortunately many of the areas are locked and password protected.

It may be beneficial with my learning to dig back into the book, grab the formulas, and build my own spreadsheet. What better way to understand the working behind the formulas!

I've attached the Drager Profiler.xls spreadsheet....

rebreatherdiver · 18th July 2008, 19:30

Entering the figures into the spreadsheet calculator I use I get 21% min. mix in the bag with a work load of 2.5 litres O2/min. This approximately equal to 50 ltr/min on open circuit and would be hard to sustain.

David

cramerdn · 19th July 2008, 09:47

Quote: (Originally Posted by GaryB)

I found this spreadsheet somewhere on Rebreather World. Unfortunately many of the areas are locked and password protected.

That spreadsheet is crap. Even if you were willing to trust a calculator where you don't know what math they are using it as other issues.

When you enter the jet size all numbers other than 32, 40, and 50 are read as zero. So even if it was working correctly a typo sends it into tail spins.

sailor · 19th July 2008, 10:40

There's a nice table in the Dolphin manual saying what 02-percentage to expect for a given jet / mix and 02-usage so i don't see the need for this sheet anyhow.

4ster · 19th July 2008, 11:53

There is a lot of good information in the sticky "CMF gas matching" at the top of this forum. Worth a read if you haven't already.

I like to keep a laminated set of tables with my Dolphin so that I can check this stuff without a computer. Attached are the tables I use. If the jets on your Dolphin are close to specification then these will give a reasonable estimate of the PO2 in your loop. If not then pm me and I will cut tables with your flow values.

17th July 2008, 19:42	#1 (permalink)
GaryB New Member Current Rebreather/s: Dolphin Other Rebreather/s: Dolphin Join Date: Feb 2007 Location: Colorado, USA Posts: 52	Diving the Dolphin I purchased a used Dolphin, had it serviced, secured a valve and tank, an Oxy2 and AirZ O2 computer, new O2 sensors, sorb, and am getting ready to dive it. I took the PADI Speciality course in January of 2006, and have been studying all the material I received, as well as other materil I've obtianed from Rebreather World, and feel or rather felt confident about jumping in the pool with it before taking it into open water. This portion of diving a rebreather wasn't covered in class... I ran through the Dolphin Profiler xls spreadsheet, and was alarmed to see that at 12 feet with a 40% O2 mix and the 40% jet, there was insufficient inspired O2. (Thanks firemandiver for pointing this out to me!!!) The profiler indicates a minimum depth of 50 feet to get the inspired O2 to 21%. This got me to thinking about a bunch of different things: 1) I need to take a rebreather refresher class! 2) how can one make a safety stop at 15 feet with the rebreather in this configuration? 3) how does one make dives shallower than 50 feet with this configuration? 4) I'm obviously missing something; see item #1 I'm hoping a rebreather refresher class will shed some light on the topic, and hoping the experience an knowledge of Rebreather World readers will help as well! Thanks! Gary
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18th July 2008, 01:00	#3 (permalink)
Dave1w Born Again Diver! Current Rebreather/s: Sport Kiss Dolphin Ray Home Build Other Rebreather/s: Classic Kiss Dolphin Ray Home Build Join Date: Jan 2005 Location: Singapore / UK Posts: 347	Re: Diving the Dolphin Are you sure? With my calcs, with an O2 consumption of 2.5 litres a minute, and 40% flowing at about 10 litres a minute, you will have at least 20% in the bag. I may be wrong, but I don't think so. You shouldn't really be able to get up to 2.5 litres of oxygen a minute, but as I understand it, Drager designed the flow for all their orifices on the dolphin to give you 20% minimum at 2.5 litres a minute of oxygen consumption. Try doing the calculation by hand with the formula in the book. Dave __________________ This message may contain spelling mistakes as it was generated by an idiot. Last edited by Dave1w : 18th July 2008 at 04:14. Reason: spelling....
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18th July 2008, 03:23	#4 (permalink)
PaulTG2 Custom Title Allowed! Current Rebreather/s: Megalodon Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Mar 2006 Location: Virginia, USA Posts: 425	Re: Diving the Dolphin Hello, I come up with 21.7% O2. I don't know what the spreadsheet uses to come up with less than 10%. (O2 injected - O2 used)/N2 injected =FiO2 ((0.40*10.7)-2.5)/(10.5-2.5)=.217 or 21.7% FiO2. That's injection EAN40% at 10.7lpm with an O2 consumption of 2.5lpm -- which is a consumption beyond what you'll sustain. Can you show the formula the spreadsheet is using? Sincerely, -p __________________ Paul's first law states that the safety of an activity is determined by how forgiving of mistakes the activity is. Paul's second law states that the difference between an adventurer and an explorer is whether the doing or the learning comes first.
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18th July 2008, 08:54	#5 (permalink)
sailor New Member Current Rebreather/s: Inspiration Vision Other CCR Dolphin Other Rebreather/s: Other CCR Dolphin Join Date: Jul 2006 Location: UAE Posts: 64	Re: Diving the Dolphin Hi, there's something wrong with that sheet. There's a lot of safety margin in Draeger's calculation. Most SCR-divers i know use one jet-size smaller then required by the used gas. According to the Draeger manual you'll never have below 20% O2 in the loop with 2,5 Ltr./min O2-usage. Nobody can use 2,5 liter O2 per minute for more than a couple of minutes because this will cause real extreme exhaustion. With your monitoring you are on the safe side anyway. When you flush your loop before ascending you are on the safe side for sure.
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18th July 2008, 19:30	#7 (permalink)
rebreatherdiver New Member Current Rebreather/s: Dolphin Other Rebreather/s: Dolphin Join Date: Mar 2008 Location: Northern Ireland Posts: 7	Re: Diving the Dolphin Entering the figures into the spreadsheet calculator I use I get 21% min. mix in the bag with a work load of 2.5 litres O2/min. This approximately equal to 50 ltr/min on open circuit and would be hard to sustain. David Last edited by rebreatherdiver : 18th July 2008 at 19:34.
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19th July 2008, 09:47	#8 (permalink)
cramerdn Obey my dog! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 612	Re: Diving the Dolphin Quote: (Originally Posted by GaryB) I found this spreadsheet somewhere on Rebreather World. Unfortunately many of the areas are locked and password protected. That spreadsheet is crap. Even if you were willing to trust a calculator where you don't know what math they are using it as other issues. When you enter the jet size all numbers other than 32, 40, and 50 are read as zero. So even if it was working correctly a typo sends it into tail spins. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
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19th July 2008, 10:40	#9 (permalink)
sailor New Member Current Rebreather/s: Inspiration Vision Other CCR Dolphin Other Rebreather/s: Other CCR Dolphin Join Date: Jul 2006 Location: UAE Posts: 64	Re: Diving the Dolphin There's a nice table in the Dolphin manual saying what 02-percentage to expect for a given jet / mix and 02-usage so i don't see the need for this sheet anyhow.
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