I've head the 1/4 turn back thing comes from the old valves that could lock open under pressure. Today's valves typically won't do that. If they do, just drain the tank through your regulator. I keep my valve fully open.
Not so. The reason for keeping valves open all the way when diving doubles is to facilitate valve shut down drills. There's only one way to turn the valve. If it's open all the way, then you don't waste time turning the valve 1/4 or 1/2 way the wrong way. Rolls offs will happen regardless of how open the valve is. Prevention of roll offs is done by staying off the ceiling.
beautybelow:I am not sure with valves these days if there is any reason not to open them all the way. I understand when diving in an overhead enviornment that opening all the way creates a "lock" and makes it harder for an accidental roll off, so I can see the "it may be dangerous" part...
Not so. The reason for keeping valves open all the way when diving doubles is to facilitate valve shut down drills. There's only one way to turn the valve. If it's open all the way, then you don't waste time turning the valve 1/4 or 1/2 way the wrong way. Rolls offs will happen regardless of how open the valve is. Prevention of roll offs is done by staying off the ceiling.