I learned this trick from Mel Clark while taking her CCR Cave course on my rEvo.
The “what if” scenario is: what if your buddy loses their O2 supply and doesn’t have off-board O2?
By default, the O2 hose going into the Manual Add Valve (MAV) is screwed on so there is no easy way to give your buddy a “squirt” of O2 into their loop that they could they breathe down and then get another “squirt” as you exit the cave, wreck, do deco, etc.
Here is a picture of the standard MAV:
One way to share O2 would be to make the O2 connector into a quick disconnect and then carry a small hose such that you could disconnect the supply and then supply either your own unit (via the offboard connector on your MAV) or to plug it into your buddy’s manual add (assuming they have a manual add on their rebreather.
Here is what it looks like:
Note the small piece of orange cave line and the O-ring. This is very important!
You don’t want the quick disconnect to get disconnected during a dive and then not have O2 when you want/need it. Therefore, you can put an O-ring into the groove on the QD connector to stop it from happening. However, this now presents another problem: how do you then remove it when you want to disconnect to share O2? Hence the small slip of cave line cinched onto the O ring. 🙂
Thanks to Mel for the great idea.