SCR Variable Flow Rates

gibbogeo

Check this (and take it easy) at step 4:

http://www.rebreatherworld.com/gener...ghtenment.html

There is the explanation of our differnt point of view.

Don't worry everybody passed the tremendous (for the other) step 4.

Only be really cautious about what you are doing. When you will understand the risk you accept now, you will be shocked.

Freef

Then we are both step 4? I would have said that we are both step five, we are having a discussion about the pro's and con's of rebreather uses, you decided to go mCCR, I decided to adjust the cylinder mixes for the diving I do.

I AM really cautious about adjusting the mixes, every dive I do I make notes to recalculate my vO2, which is slightly higher in the water temperatures I am diving at the moment [4-6 deg C], and I dive with a pO2 gauge.

I understand the risks I am taking, and I appreciate them every time I dive, whether it is OC or SCR. Seeing someone on OC being dragged out of the water yesterday and flown to hospital is a reminder of how dangerous diving is. With a pO2 gauge you monitor the loop pO2 and fO2 the same way you would if you were diving either the factory standard settings or CCR.

Have you worked out your vO2's for 'normal' and 'hard work' diving? If you have then you can see how you could adjust the flow rates for the Dolphin as standard.

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David.

Diving the mahogany rebreather.

EBT

For the sake of keeping daves thread clear, I've started a new thread on KISS, CCR or Posh SCR?

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gibbogeo

No, i am still at step 3. That's why i am so worried about your habit. And that's whii i don't think it is possible to have a Po2 in the loop higher than the one you have in the bottle, like you do. Maybe when i will reach step 4 i will agree with you.

No, i am confident with the value set by the factory. When i needed to extend the dive time I used a bigger bottle (8 or 10 l) and when i wanted to go deeper i used a second mix with an additional ray jet (this happened after around 120 hours of use. After 30 more hours I added a kiss valve, an oxgen bottle and three sensor and started again to learn).

I never played with gasses and mixes. Ad i have seen what can be the results to tell anybody to do this.

Nick uk.

Cioa Gibbo. Looks like your having problems with your English as i sometimes do with my Italian.

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caveseeker7

Sensible thinking given that the Dräger has a 200 bar fill pressure.

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Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

gibbogeo

I agree.

but i have the same kind of problem also in italian, when i type too fast.

Freef

I still haven't seen the chap I was diving with when he hit a pO2 of 1.7, so I can't tell you what his mix and jet size was. The pO2 in the loop when I dive is lower than the pO2 in the tank, and lower still when I mix the jets.


But even with the standard jets you should use a pO2 meter to determine your vO2 to optimise the Dolphin. Otherwise you will be diving after planning your loop fO2 to be 21%, as you will never know what it is with any certainty, and you will have a maximum depth of 1.4 bar pO2 of whatever tank mix you are using. This will have all the disadvantages of both air diving [the short no stop times] and nitrox diving [the maximum depths].

If you know your vO2 ranges from normal to heavy work load you can set your computer to an appropriate loop fO2 setting and have a longer no deco dive, or reduce your deco commitments. Section 5.2 of my original post shows that with a vO2 of 1.1 and using 50% through the 50% jet, the loop fO2 would be 41%

If you adjust the gasses and jets without a means of monitoring pO2 then you may get into trouble, if you monitor yout pO2 you aren't likely to. I am not recommending that anyone does try this method of extending the Dolphins capabilities if they are not prepared to do the monitoring dives to ensure they reduce the risk as much as possible. The formulae apply to other CMF SCR's, but as I am only familiar with the Dolphin I can only comment on that particular unit.

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David.

Diving the mahogany rebreather.

Underwaterbear

I dont usually throw my worksheets around on the net but here it might be relevant. This a spreadsheet I used to use with my Azi. Two gases, one preset flow rate (although you see a different rate in the spreadsheet since the IP on the second reg is set to allow preferential flow).

Play with the "single gas" sheet to emphasize Bowies point.

Check out the "two gases" page - play with the FsO2 values. The high value sets the flow rate (based on the Azi manual recommendations).

The graph shows you the switch points and emphasizes why compared to the Dolphin, the azi is a much superior 2nd rate rebreather

PS: No responsibility taken for the calculations in the spreadsheet. Intended as an educational device only. YMMV.

Attached Files

Azimuth flow rates.zip (11.6 KB, 9 views)

Freef

Grrrrr.....

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David.

Diving the mahogany rebreather.