Quote: (Originally Posted by
grazie42)
But if your gas-plan is ok (it should be as you´re DIR), you´d never need more than half your backgas to get out anyway...the "extra" gas you may save by closing the "right" valve first has no real survival value to you, while losing more than half could potentially get you killed...
Let´s say you dive 1/3s (the least conservative) and something happens just as you turn the dive. You can either:
1. Close your isolation valve, have a worst case scenario of ˝ your BG left (=1/3) which is still enough for you to get yourself out.
or
2. Close whichever post you´re guessing has the problem, have a worst case scenario where you´re basically OOG.
I might have this wrong so bear with me
As i understand thirds its a third of the gas required to get you to the farthest point from the next available gas source and two thirds to get you and your buddy back from there to the next gas source.
On an OW dive if your next available gas source is 21m on 50% you could theoretically run your gas supply down to a few mins of gas needed to get you and said buddy from 60 to 21m?
At that point (yes I know its massively unlikely) a free flow could empty back gas before you got it sorted out.
QED the fastest way of saving gas is the best way.
So the argument is, is going for the primary reg post the fastest way to guarantee some gas reserves?
Obviously TDI we are taught to isolate the center valve first to guarantee 50% of remaining gas.
Just for "Comedic value" :D I used to do the isolator and the primary reg post at the same time. Isolator was only two turns open so took a second or so, primary took how ever long it took (I had good days and bad days) but significantly longer than the isolator.
ATB
Mark Chase