Hog wrapping a bail out hose under a loop on a rebreather.

[PfcAJ]

Not necessarily. On SCR the only way to increase or decrease your ppO2 is to change the fO2 of the injection gas. RB80 is more reliable in a sense, depending on the operator. CCR could be considered more reliable in another sense as it will try to maintain a breathable loop without human input.

So take a CCR, you can dive 10/70 diluent and the machine (via solenoid or the orifice & MAV) will inject oxygen to make up the difference so you have a breathable loop on the surface, no switching going down or up. You can dive that on a 60m dive if you wanted with 2 BO cylinders (untouched). As an eCCR, the JJ in good condition could do this "dive" without any human intervention. Not that you would dive without monitoring the loop, but it is designed to try to keep the loop at your specified ppO2.

If you want 10/70 gas on the bottom on an SCR you need to bring higher fO2 injection gases to start on, descend on, and switch on the way down, then again on the way up. This dive on SCR would take quite a few cylinders (probably O2, 50%, 21/35, 10/70) - you'd be (manually) switching to them both up and down. If you don't maintain a rigorous switch protocol you will die. This is how Jim Miller died.

The need to switch on the way down isn’t that dramatic. On a deep ocean (say 300’), I’ll breath the 35/25 bottle on open circuit to 20’, then through the loop down to 120, then switch to 12/85 through the loop for the rest of the bottom phase. Then on the way up plug in as a normal oc ascent, but through the loop. You need those bottles for open circuit bailout anyways, so they’re coming with you no matter what.

There are other techniques, but this works pretty well. Not as simple as CCR, but not chaos either. It’s more like open circuit diving than anything else.

 

[rjack321]

The need to switch on the way down isn’t that dramatic. On a deep ocean (say 300’), I’ll breath the 35/25 bottle on open circuit to 20’, then through the loop down to 120, then switch to 12/85 through the loop for the rest of the bottom phase. Then on the way up plug in as a normal oc ascent, but through the loop. You need those bottles for open circuit bailout anyways, so they’re coming with you no matter what.

There are other techniques, but this works pretty well. Not as simple as CCR, but not chaos either. It’s more like open circuit diving than anything else.

Yeah I was only trying to point out the switches are an integral part of diving SCR like they are on OC.

I havent done any 300' dives on OC but on CCR I havent used a 35/25 gas for those. 10/70+ dil then BOs of 12/65, 21/35, 50%, O2.

 

[PfcAJ]

Yeah I was only trying to point out the switches are an integral part of diving SCR like they are on OC.

I havent done any 300' dives on OC but on CCR I havent used a 35/25 gas for those. 10/70+ dil then BOs of 12/65, 21/35, 50%, O2.

There’s an argument to be made for taking 21/35 over 35/25. Pros and cons to each.

With the RB80 though, 21% isn’t breathable through the loop till you’re fairly deep so it’s generally my go-to. I’ll add on a 21/35 bottle for certain cave dives, but generally not in lieu of 35/25.

Both work.

 

[lermontov]

No, whatever gas you have plugged in is what you’re breathing. Generally, caves tend to be fairly constant in depth. For deco, just plug in whatever gas you want. Just like OC.

Rb80 is a bit smaller due to not needing an oxygen cylinder. It’s often paired with real big tanks due to bailout requirements.

CCR uses less gas, for sure, but the amount of gas an RB80 uses on even a preposterously long cave dive is negligible in the grand scheme of things.

so im assuming your deco is monitored by switching your preset gasses on your DC each time you switch feeds

 

[rjack321]

so im assuming your deco is monitored by switching your preset gasses on your DC gauge each time you switch feeds

fixed it for you

 

[PfcAJ]

so im assuming your deco is monitored by switching your preset gasses on your DC each time you switch feeds

Correct. Or by lookin at your tables. Or both.

 

[Wibble]

Records have such better sound quality than digital.

Who needs a computer when you can use a slide rule.

CAN-bus; two tin cans and some cave line

 

[PfcAJ]

Records have such better sound quality than digital.

Who needs a computer when you can use a slide rule.

CAN-bus; two tin cans and some cave line

It’s ok if you don’t get it.

When you’re lookin at 6-10hr (or longer) dives, people flying in from literally around the country to support, and diving windows that are days long (not weeks. Days), reliability becomes an important feature. The rb80 accomplishes this while totally eliminating unit-induced hyperoxia.

 

[Wibble]

It’s ok if you don’t get it.

When you’re lookin at 6-10hr (or longer) dives, reliability becomes an important feature. The rb80 accomplishes this while totally eliminating unit-induced hyperoxia.

I do get it. However, that use case is somewhat esoteric.

SCRs do have a place, especially where HP oxygen isn’t available. They’re not very frugal with helium though, so deep dives would count a bit.

 

[PfcAJ]

I do get it. However, that use case is somewhat esoteric.

SCRs do have a place, especially where HP oxygen isn’t available. They’re not very frugal with helium though, so deep dives would count a bit.

It’s what the unit was designed to do…