Question CCR for recreational depths

[billgraham]

All that may be true, but the discussion is (or at least was) about whether that MCCR is more dangerous when shallow than that same MCCR is when deep, not whether MCCR or ECCR is more dangerous overall.

Having spent a bunch of time diving both, I'd say that the MCCR does connect you more closely with what's going on in the loop, but it makes things like photography (or doing a tie in) more complicated because you're doing more with your hands as compared to the ECCR. Decompression is far easier with a CCR than an SCR or OC. You're doing nothing except maintaining the PPO2 in the loop.

 

[TuckerIdaho]

Rebreather's are not for everyone. This is the attitude thing. You must take care of the rebreather; you must do the post dive maintenance; you must do thorough cleaning; you must store it correctly; you must use checklists for assembly; you must use checklists when you kit up and turn the unit on; you must be pedantic and that final check before you jump in. Preparation will be hours in the early days. Rebreathers are most definitely not for people who throw their kit into a heap and leave it.

You say this like some of us don't enjoy the fiddly, process oriented, checklist oriented nature of them.
I'll admit it, I enjoy running through my checklists.

 

[MidOH]

I also enjoy tinkering to get the most out of my rig.

When din wasn't working out so hot, in the Caribbean, buying a yoke reg was no big deal.

I've got a box of every necklace reg hose in 2" increments. To get it just right. Do I want it tight to my neck, loose, or falling over the corner of my shoulder. Just a matter of choice every week. Primary reg has a 40", 5', an 7' hose to pick from. I havent quite dialed in my inflator hose, but Im close.

So cost and complexity, takes a back seat to just getting it perfect. Getting the hoses just right, did make diving more fun. Maybe its just habit from ultralight backpacking, where everything is streamlined to the max.
Even our toothbrushes.

 

[billgraham]

You say this like some of us don't enjoy the fiddly, process oriented, checklist oriented nature of them.
I'll admit it, I enjoy running through my checklists.

Meh, if I could take a pill and breath water, I'd do it!

 

[inquis]

How far below setpoint does a typical eCCR allow the PO2 to drop before injecting oxygen? (I'm most curious about the O2ptima CM if you happen to know that.) In other words, how tight is that control system (0.01 atm, 0.1 atm, etc.)?

 

[broncobowsher]

How far below setpoint does a typical eCCR allow the PO2 to drop before injecting oxygen? (I'm most curious about the O2ptima CM if you happen to know that.) In other words, how tight is that control system (0.01 atm, 0.1 atm, etc.)?

I'm going off memory here as I typically don't let the solenoid fire and manually control the PPO2. But I want to say it is a combination of PPO2 and time, not just PPO2. That is if the PPO2 drops 0.1 below setpoint it does NOT fire right away. But after several seconds it finally will. Say you add a shot of low O2 DIL, that passes the cells and reads low. It will give you a few breaths to mix it in before deciding you are actually low on PPO2 and add some for you. But I can't say everyone does the same.

But if I change setpoint from .19 (surface) to .70 (start of dive), it fires right away. That is severally off target, so I see it would want to fire now instead of waiting to see if things will fix themselves.

 

[Heat Miser]

How far below setpoint does a typical eCCR allow the PO2 to drop before injecting oxygen? (I'm most curious about the O2ptima CM if you happen to know that.) In other words, how tight is that control system (0.01 atm, 0.1 atm, etc.)?

On the chop it seems to fire every 2-3 millivolts, so compared to a CCR with a CMF or needle valve the PP02 bounces around a bit.

 

[Heat Miser]

You say this like some of us don't enjoy the fiddly, process oriented, checklist oriented nature of them.
I'll admit it, I enjoy running through my checklists.

I had allways hated checklists, I had worked in heavily regulated financial services and check lists to me seemed to be for middle office people that really didn't understand what was going on ... their job was to tick and flick. I thought if they didn't know enough about the business to memorise the checklist, then why should they be tasked as being the businesses gatekeepers.

My views have changed with a CCR,

I had never done anything life threatening like flying a plane, for example, and I now understand how easilty it is to rush through a checklist and miss a point, during the pre flight excitement of the moment. I was probably overly skeptical about the value of those independant set of eyes looking over things checking for errors.

 

[TTPaws]

How far below setpoint does a typical eCCR allow the PO2 to drop before injecting oxygen? (I'm most curious about the O2ptima CM if you happen to know that.) In other words, how tight is that control system (0.01 atm, 0.1 atm, etc.)?

From my AP Inspo manual "If the PPO2 is 0.1 bar or more below the setpoint, the solenoid is opened."

Lately I am a photographer, so I run in auto, checking it once in a while, but concentrated on my pictures.

 

[Dsix36]

I'm missing how this is true since the fraction of O2 is greater when shallow for a given PO2. My understanding is that the density should be constant (assuming PO2 is maintained). Unless you're talking about an intentional difference in setpoint?

Example:
On the surface you have a one gallon baggie of gas with exactly 100 molecules of oxygen in it. We all know that at 33' (one atmosphere deeper than surface) the volume of gas will be halfed by the pressure. Thus you will have same amount of gas in the baggie but it will take up half the area. To have the same area taken up you would have to double what you stated with so you add another baggie (and another 100 molecules of oxygen). Now you suddenly have 200 molecules of oxygen. Extremely simplified and I know someone will criticize my terminoligy.