I see a lot of people open the valve all the way then back a half turn. Not sure why. If you get that reversed I can see a big problem. Close it when you think you are opening then half turn open.
I just open mine all the way. Also test it. Sent from my iPad using Tapatalk HD
Its normal practice with all valves unless back seated. The reason mainly is that if you open a valve the back it off a little, it becomes immediately apparent if you try and open it further with the intent to close it and hit the stop that you are going in the wrong direction. If the valve is already fully open and you turn it further it can jamb and then be stuck open.
An example is a valve that is really really tight. You turn it and are not sure if its the right way so most people naturally then try it the other way. Now they find it hard in both directions. Immediately confusion and uncertainty sets in. Which way to move it? We all know in the back of our mind that most single valves close clockwise and open anti clockwise, and yet in this situation we are unsure. We are also unsure if its wide open (particularly if stuck fully open) or closed? It also indicates that the valve is open (to some degree). If you back seat it "fully open" is it open or closed? with it not hard against the back stop its simple to test the valve to see where it is, a simple turn anticlockwise shows it was nearly fully open.
Also its standard procedure and if we all try and stick with standard procedure then in a crisis its easier for anyone to assist as we ALL have familiarity.
---------- Post added October 15th, 2013 at 03:52 PM ----------
You will be surprised at the number of divers who have at least once in their life, tried to dive with their air off. I know I did when I was first starting out, and as I reached the jump off point my air valve was checked by the dive boat assistant and her turned it on. I NOW ALWAYS suck from both my regs with gauge in hand to see that the tank pressure remains steady, a good sign my air is on and ok, all before I reach jump off point, but just before I go.
I heard of a story of a very experienced diver in Port Phillip bay (>700 dives) jump in with twin steels and go all the way to the bottom, no air on. Needless to say he is no longer with us. It can happen to anyone, no matter their experience level or knowledge. We ALL have bad days. the more routine you make the checks and tests the better it is from a point of not missing anything, not in a manner of doing it in a dream state, but in a form as pilots do; 1, 2, 3 , 4, 5 every time.
---------- Post added October 15th, 2013 at 04:00 PM ----------
Another incident we had early in our diving career which might be along the lines of what happened here. My wife went diving, before she went in her occy would slightly free flow, suck from it or hit it and it would stop. Soon after it would slightly leak a little again. We went in the water to test it and all seemed well. We used it an 3 dives but it seemed the same when above the surface. We took it in for a service and found the primary reg stuck with swarf material in it from when it was built. The line pressure was creeping up slowly thus it would slightly free flow, but soon as you sucked on it the line pressure dropped and it stopped free flowing. Had she of used it at significant depth it would not have provided sufficient air as the line pressure would have fallen right off. Without a buddy or over weighted with an uncontrolled descent it could have meant death.