Rebreather descent on Open Circuit?

[Peter Guy]

I am NOT a CCR diver so please forgive me if this question is too ignorant for words for I am ignorant when it comes to CCRs.

I'm making one assumption here that the OP is diving the Mk 6 and if I'm wrong here, then, nevermind.

It is my understanding that the whole idea behind the PADI "R" type rebreather (Mk 6) is that EVERYTHING is automated -- there is, and can be, no user intervention. (And no, I don't want to get into the discussion regarding whether this is good, bad, indifferent or even possible.) IF this is the case, that everything is automated (PPO2 constantly checked) how could there be a problem descending/ascending? What problem did the instructor think he was solving by having the OP go to OC on descent?

Again, please forgive the ignorance which led to this question.

Thank you.

 

[Packhorse]

I am NOT a CCR diver so please forgive me if this question is too ignorant for words for I am ignorant when it comes to CCRs.

I'm making one assumption here that the OP is diving the Mk 6 and if I'm wrong here, then, nevermind.

It is my understanding that the whole idea behind the PADI "R" type rebreather (Mk 6) is that EVERYTHING is automated -- there is, and can be, no user intervention. (And no, I don't want to get into the discussion regarding whether this is good, bad, indifferent or even possible.) IF this is the case, that everything is automated (PPO2 constantly checked) how could there be a problem descending/ascending? What problem did the instructor think he was solving by having the OP go to OC on descent?

Again, please forgive the ignorance which led to this question.

Thank you.

On quick descends you need to quickly pump lots of gas into the lung to keep enough gas in it to breath from. This is usually done by the ADV which depending on how its set can be quite hard to activate. Basicly you need to suck really hard to get any gas.
With a DIL MAV you can just push a button and pump more DIL gas in whether you are breathing in or out. But if it cant flow enough gas because you are descending to fast then you run out of gas to inhale from the lung.

My solution is simple. When I feel the lung bottoming out I open up my BOV and take a big breath of OC gas, close the BOV and exhale into the counter lung. Depending on the unit and your trim you can even slightly open the BOV and leave it that way on the descent.

I have stopped using my DIL MAV now and use my BOV and ADV to add DIL gas when ever I need it.

 

[mathauck0814]

I have stopped using my DIL MAV now and use my BOV and ADV to add DIL gas when ever I need it.

+1, Use the ADV on descent. Descend slower and it won't be such an emergency.