I have tried a couple of my tank valves, and at 1/4 turn open they will pass any but the most aggressive tank check. My training was to make the tank check to insure you had air, not to check if the tank was open, which can only be done by checking the valve itself. If you have a problem getting air as you decend, surface and check the valve first.
Agreed.
Out of interest, I've just check my tanks and valves (bored today)
Each of my valves has 3 compete revolutions of the hand wheel from open to close. The spg will only have some deflection for the first one half of a turn (or 16% of total operation of valve) After that it remains stable. Purging (obviously) gets a bigger deflection over breathing
This is why I teach ( and perform) physical checks on my valves to ensure fully open, and the "standard breathing test" just shows if the tanks has been opened and closed or is just open a "crack". I consider it bad practice to leave hoses pressurised with the tank valve off.
One of the downsides of Neg entries or "hot drops" is that divers become task fixated on the way down, and could easily be transitioning into something akin to a lawn dart when they lose gas pressure (through a partially closed valve).
While I can reach my valve in a controlled no pressure situation (in a pool demonstration the gas off skill during OW) I'm under no illusions, that f it happened for real the fastest and surest way to reach my valve would be to slip my left arm out of my strap, twist my rig round and access it that way. Something I've practiced many times - but (touch wood) never needed in real life.
I try to instill in people that they should consider the "what if", have a contingency, practice and refine it. It's' never the best to assume that a plan/procedure you've read about on the internet will work in a time of stress. Worse still if someone finds out it actually doesn't.
Thank you!
