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The turn half/quarter back is to ensure that the valve doesn't get stuck in the OPEN position.
This is absolute rubbish! An open valve that's stuck is not an issue at all. You wait till the cylinder is emptied and then have the valve repaired/replaced.
What IS an issue is a valve that is stuck CLOSED! what you gonna do then? 232 bar with no way to get it released!
more importantly is this, and it HAS HAPPENED.
An instructor doing a buddy check with a student asks during the BWRAF if the air is on. The student feels the valve and turns it all the way OFF, then back on a half turn. At the surface this gave enough air to continue registering on the SPG. The two breaths taken at the surface didn't feel bad at all.
Upon entering the water and descending, the instructor finds that the air is not ON and is having difficulty pulling air through the reg. The student stares WIDE EYED at the instructor because he is giving OUT OF AIR, and the student backs away because he don't know what the heck is going on!
This ACTUALLY HAPPENED.
therefore in our school, air is TURNED ALL THE WAY AND NOT BACK BY ANY AMOUNT. if the gauge reads and you can pull air, then its on. If not Its OFF!!
Lots of great rumor material here, but can anyone point me to that actual documentation that supports that "valve sticking in open position" nonsense?
We encourage our divers to open valves fully for maximum flow, then turn back a 'skosh', just enough to satisfy any inquisitive hand that may touch your valve to ensure it is open on the way to the water.
I like all the bravado about "no one touches my valves" but I wonder how many actually realize how many DM's or boat captains do one last check on your valve before you splash. As if that's a bad thing?
Ultimately it is the divers responsibility to ensure his/her gas is flowing and valves are open by taking a few good 'huffs' on your regulator while watching your primary gauge. If gas flows and gauge doesn't move, that is generally good. If gas flows but gauge reading drops, might be a good time to turn your valve to the 'open' position! No in-water surprises that way!
Before I took my cavern class a week ago I had to read not only the NSS-CDS cavern manual, but I had to read Sheck Exley's Basic Cave Diving: A Blueprint for Survival. On page 22, he talks about the actual dangers of turning your valve a quater or half turn. Here is a quote from the book:
"During the dive both valves are turned on all the way "(refering to doubles) "Do not turn the valve on all the way, then half a turn back as some diving manuals reccommmend. On more than one occasion cave divers have forgotten they had already turned on thier air, then unwittingly turned their air all the way off and back on a half turn. The result was a constricted orifice that made the diver seem to run out of air when his pressure got down to 1500 psi! It may sound ridiculous, but this writer and others have almost drowned from just such an incident. A handy way to remember which way to turn your valve is the word "cough" (coff), which stands for Clockwise= off. Counterclockwise is always on.
By having both valves turned on all the time, regulator malfunctions during the dive can be ascertained as soon as they occur. Further, if a regulator does malfunction, all you have to do is turn off the valve going to it, rather than turn one off and also turn one on as would be the case if one valve was left off instead."
For this reason you will see most divers who are cavern or cave trained keep their valves open all of the way. This way they know it is either on or off.
“From birth, man carries the weight of gravity on his shoulders. He is bolted to earth. But man has only to sink beneath the surface and he is free.” -Jacques Cousteau
When I first started teaching I would teach the full on then 1/2 turn back routine.
A few years ago I studied cave diving and learned to turn my air all the way on.
Now my air is either on or off.....not somewhere in between.
Try turning your valve a 1/4 to 1/2 on....... you will get air at the suface but not at depth.
If my valve is off I won't get any air at the surface, I know that I need to turn on my air.
Found the shot where I had the company name. Scuba Stik LLC, and the product is called the "Vindicator," incase anyone was interested in looking up the valve knob that shows you if it's on or off.
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