Getting the most out of your O2 tank

**PhilSiswick** · 24th May 2007, 08:58

Quote: (Originally Posted by nigelh)

I'm going on holiday in a fortnight and I'll take a J of O2, a J of Helium and the Haskell so you probably can guess I don't really care about consumption that much.

That's more like it!

Cheers,

Hanssing · 24th May 2007, 09:48

Quote: (Originally Posted by PhilSiswick)

Is that right? I'd have thought that, if you have a low setpoint, the gas you'll be dumping will be made up more of dil than O2, because you'll be putting less O2 in to the mix that you are dumping. In my (admittedly limited) experience with the Vision, I'd say that there is a noticeable difference in the gas that you dump if you ascend on 1.3 rather than 0.7 - all of that difference has to be O2, as you're not adding any dil.

Hmm, you are quoting me out of context

What I was saying, is that for any given setpoint, the amount of "wasted" O2, ie. O2 not metabolized but release to the water, during ascent, is independant of ascentspeed. Reason, assuming a constant total loop-volume during the ascent, the volume released will only dendent on start-depth. Since PP02 is also constant, then it follows, that wasted O2 only denpends on PPO2-setpoint, and Total loopvolume.

When ascending with a low setpoint, say 0.7, you waste less O2, than when ascending with 1.2. I still say that the amount is independant of ascent-speed!

Quote: (Originally Posted by PhilSiswick)

I think you've got that the wrong way around - empirically, it feels as if the unit is putting a hell of a lot of O2 in shallow to keep the PO2 at 0.7. That's a pretty high FO2 to maintain. I agree with you about the loop volume to a point, but I think you should be focussing more closely on loop volume shallower, as it's amazing how much bouyancy change you'll get from one injection from the solenoid (which it'll be doing more often at this depth).

Yes, what I meant to write, was that you should/could focus on both at shallows. The advantage of keeping the high setpoint at lower depth, was to avoid hypoxic loop-content at surface pressure.
The amount of O2 (moles/free O2) released to the water from say 40-39m or 5-4m, with the same setpoint are actually not same (think about it).
So therefor the method is actually not independant of depth, and is more effective when shallow.

Quote: (Originally Posted by PhilSiswick)

Of course, I stand to be corrected on all of this. I'm a newbie too, but this is based on what I've experienced, mapped back to what I think I know. I'm also sitting at my desk in London, not diving, so who knows?

We'll see when I get my own Rebreather

I lost the spreadsheet calculation I did originally . So the attached sheet is a new one.

Dutchy · 24th May 2007, 11:58

Quote: (Originally Posted by nigelh)

... Hence an intelligently driven MCCR might outperform our computer controlled systems if O2 consumption is that important to you...

Lowering setpoint to .7 does't mean you have to dive that setpoint. There's still the option of keeping it on 1.3 manually while using the .7 setpoint as a safety-net that kicks in when you screw up the manual management.
Doing that would give you the MCCR advantage while still enjoying the ECCR ones.

**PhilSiswick** · 24th May 2007, 12:33

Quote: (Originally Posted by Hanssing)

Hmm, you are quoting me out of context

What I was saying, is that for any given setpoint, the amount of "wasted" O2, ie. O2 not metabolized but release to the water, during ascent, is independant of ascentspeed. Reason, assuming a constant total loop-volume during the ascent, the volume released will only dendent on start-depth. Since PP02 is also constant, then it follows, that wasted O2 only denpends on PPO2-setpoint, and Total loopvolume.

When ascending with a low setpoint, say 0.7, you waste less O2, than when ascending with 1.2. I still say that the amount is independant of ascent-speed!

Got it - couldn't agree more. Sorry I misunderstood the first post.

Quote:

Yes, what I meant to write, was that you should/could focus on both at shallows. The advantage of keeping the high setpoint at lower depth, was to avoid hypoxic loop-content at surface pressure.
The amount of O2 (moles/free O2) released to the water from say 40-39m or 5-4m, with the same setpoint are actually not same (think about it).
So therefor the method is actually not independant of depth, and is more effective when shallow.

Also agree - it's an interesting point.

Quote:

We'll see when I get my own Rebreather

Enjoy it when you do - it's tremendous fun (especially having these conversations!

Cheers,

Jordan · 24th May 2007, 13:42

My advice to lower your o2 consumption is to also chill baby chill but more importantly -- never exercise again and become as out of shape and as fat as you possibly can.

24th May 2007, 08:58	#31 (permalink)
PhilSiswick Phil Siswick, Tango Current Rebreather/s: Evolution Other Rebreather/s: Inspiration Vision Join Date: Apr 2006 Location: Oxford, UK Posts: 991	Re: Getting the most out of your O2 tank Quote: (Originally Posted by nigelh) I'm going on holiday in a fortnight and I'll take a J of O2, a J of Helium and the Haskell so you probably can guess I don't really care about consumption that much. That's more like it! Cheers, __________________ Phil (WSKD 0001) I have always felt that the dive I am on is not nearly important as the dives I plan to be on the rest of my life. Tom Rose, 2007 The person who gets the farthest is generally the one who is willing to do and dare. The sure thing boat never gets far from shore. Charles A. Lindbergh www.hugsac.org.uk
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24th May 2007, 11:58	#33 (permalink)
Dutchy Rene Warries Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 764	Re: Getting the most out of your O2 tank Quote: (Originally Posted by nigelh) ... Hence an intelligently driven MCCR might outperform our computer controlled systems if O2 consumption is that important to you... Lowering setpoint to .7 does't mean you have to dive that setpoint. There's still the option of keeping it on 1.3 manually while using the .7 setpoint as a safety-net that kicks in when you screw up the manual management. Doing that would give you the MCCR advantage while still enjoying the ECCR ones. __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. =
(Online)

24th May 2007, 12:33	#34 (permalink)
PhilSiswick Phil Siswick, Tango Current Rebreather/s: Evolution Other Rebreather/s: Inspiration Vision Join Date: Apr 2006 Location: Oxford, UK Posts: 991	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Hanssing) Hmm, you are quoting me out of context What I was saying, is that for any given setpoint, the amount of "wasted" O2, ie. O2 not metabolized but release to the water, during ascent, is independant of ascentspeed. Reason, assuming a constant total loop-volume during the ascent, the volume released will only dendent on start-depth. Since PP02 is also constant, then it follows, that wasted O2 only denpends on PPO2-setpoint, and Total loopvolume. When ascending with a low setpoint, say 0.7, you waste less O2, than when ascending with 1.2. I still say that the amount is independant of ascent-speed! Got it - couldn't agree more. Sorry I misunderstood the first post. Quote: Yes, what I meant to write, was that you should/could focus on both at shallows. The advantage of keeping the high setpoint at lower depth, was to avoid hypoxic loop-content at surface pressure. The amount of O2 (moles/free O2) released to the water from say 40-39m or 5-4m, with the same setpoint are actually not same (think about it). So therefor the method is actually not independant of depth, and is more effective when shallow. Also agree - it's an interesting point. Quote: We'll see when I get my own Rebreather Enjoy it when you do - it's tremendous fun (especially having these conversations! Cheers, __________________ Phil (WSKD 0001) I have always felt that the dive I am on is not nearly important as the dives I plan to be on the rest of my life. Tom Rose, 2007 The person who gets the farthest is generally the one who is willing to do and dare. The sure thing boat never gets far from shore. Charles A. Lindbergh www.hugsac.org.uk
(Offline)

24th May 2007, 13:42	#35 (permalink)
Jordan EBT called me stroppy! Current Rebreather/s: Optima Other Rebreather/s: Join Date: May 2005 Location: Garner, NC Posts: 226	Re: Getting the most out of your O2 tank My advice to lower your o2 consumption is to also chill baby chill but more importantly -- never exercise again and become as out of shape and as fat as you possibly can. __________________ Is it clear? No. Well, let's go anyways. "Those who would sacrifice a little freedom for a little order, will lose both, and deserve neither." Thomas Jefferson
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