OOA after only a few minutes with a full tank at 17m

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The appropriate hand signal when you see the boat boy make a move towards your gear is this. While smiling, hold your hand palm down and wave it back and forth twice followed by an ok symbol. That usually does the trick.
 
Regarding the partial re closing of valves. On most industrial / welding gas cylinders if you open the valve fully it will leak, the harder you force it fully open the more it will leak. Scuba valves are probably different, certainly they don't leak like the gland seals on welding gas cylinders. With welding gases, to prevent gas wastage (or an explosion if using acetylene) the valve should always be closed slightly from fully open position. Also on water systems with gate or stop valves the valve should not be left fully open or it will likely seize in that position.
I am guessing that the seals on scuba valves are pressure activated, ie the greater the pressure in on the seal the greater sealing force it exerts. This is different to welding gas valves and water taps where the sealing force is only applied mechanically.
 
I’ve switched to all on (or all off), I also look at my gauge when testing the gear on set up.
 
Did you just describe opening and closing a valve?

Im not joking
Yes. A way to determine which way to turn it when you are not oriented directly facing the valve (ie when lefty loosely rightie righty doesn’t work)
 
My OW instructor was Tim Mitchell (RIP) on Catalina. He was the most amazing, patient teacher. He passed away much too young, trying to save a boat in a storm.

One thing he taught me--and told me he did himself before every one of his countless dives:
Just before you put your primary in your mouth, hit the Purge button briefly while watching your SPG--if the needle bounces at all, the valve is not open all the way. Since the purge valve blows air off a lot faster than you would by taking a breath or two, this should work as a reliable final check on the surface and obviate the need to remember to check again during descent.

Of course it's a good idea to look at your gauges early and often underwater, but on some (drift dives especially), you have to descend 60-80 feet in a minute or two, and what with equalizing along the way and maintaining as much situational awareness as possible, it is nice to know that you are completely confident about your air being "on" all the way when you first hit the water.
 
The appropriate hand signal when you see the boat boy make a move towards your gear is this. While smiling, hold your hand palm down and wave it back and forth twice followed by an ok symbol. That usually does the trick.

Reminds me of a dive in the PP - just as I turned around to pick the straps of my BCD to don the gear, the boat boy started rotating the valve all the way OFF and confidently made a half turn back after it was fully shut. I was appalled as I had just turned it on a few minutes back as the boat was slowing down to a stop. The needle was at 220bar when I had last checked and done the breathe test, and If I had turned my back to him for some reason to check my gopro rig or something and simply glanced at the pressure guage before doing the back flip ... I still remember the incident and possible what-if(s) with horror.

I now remember to do the breathe test once again after I am fully strapped in...

P
 
Taking the positives out of this, you just received your greatest ever training experience as a DM candidate. You handled the situation and the diver exited the water without injury. That's it, job done!

We drill and coach DM's on emergency situations but, in the end, they are just exercises. With students I'm forever telling new DM candidates to get closer and be vigilant rather than farting about showing of their buoyancy skills. When a student bolts, you'd be surprised how quickly they can move.

A real life potential emergency teaches you not just the muscle memory but how you will genuinely respond. It's also quite normal to retraumatise after an event and over analyse what you could have done differently. Don't, you did fine!
 
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