Full on, and a little off

[faze]

Would love some genuine feedback on this...

"Turn the tank fully on and then one quarter/half turn back"..

That's what I was taught...

Why...?

 

[rhwestfall]

that was then, this is now:

Indicator Tank Valve

and open them all the way, just don't ham-fist them....

 

[faze]

Well for the thousands of dive centers that haven't chosen to replace all their valves overnight.

Surely we just turn on fully?

 

[Hickdive]

It's an old engineer's trick of the trade. If you turn back a quarter and then someone tries to "open" the valve then they'll instantly feel that the valve is already open. If the valve isn't turned a quarter back then someone trying to "open" it might wrongly think that it is stuck closed instead of being against the open stop. They then might try to force it "open", damaging the valve and possibly even jamming it open. In an commercial engineering setting that might mean an expensive process gets stopped whilst a valve is fixed. In a military engineering setting such as on a ship it could be disastrous.

Whether this is relevant or necessary in scuba diving is open to debate - as you're about to find out.

 

[Dr. Lecter]

In diving, taking it off the stop gives the dubious benefit of allowing some slop should the valve strike an overhead or other obstruction and be forced further in the 'open' direction. I make sure my personal valves are neither hard closed nor hard open, but that's for valve component longevity rather than safety. Rental tanks, I couldn't care less how fully open or closed they are.

The 1/4 turn is, to me, excessive and leaves enough turn-ability in both directions as to invite someone (like a busybody DM or buddy) to accidentally turn it off. This just gets more complicated once doubles are involved, since the valves turn in opposing directions. There's also the issue of how many turns it takes to close - some valves must be turned many times, and a full 1/4 turn back for them may be just right. Others, like Halcyon, only take a few full turns to go from open to shut...hence my finding 1/4 turn too much.

Note that none of this applies to isolator valves on manifolds...those have the added issue of some preferring to keep them fully closed and open a 1/4 turn

 

[grf88]

The quarter turn that kills

 

[Dr. Lecter]

If your scuba tank is only partially open, you may very well die.

Absent drysuit shrinkwrap issues not contemplated by that article's argument, that should not be the case. If you cannot easily reach back and open the valves, you have bigger problems than suddenly finding your reg no longer delivering much air at 100' or 200'.

 

[tphelps]

The quarter turn that kills

Great article. For a years I've been teaching the fully turned open but quarter turn back to minimize galvanic action on the valve. But in my experience in tech diving, we always turn them all the way open or closed. There have been times too when I have checked students before going into a dive where they in fact only had a quarter turn on instead of fully open and quarter turn back.

I've enjoyed reading the comments in this thread and I think I'm going to start teaching fully open. Thanks everyone!

 

[Steve_C]

A If you cannot easily reach back and open the valves, you have bigger problems than suddenly finding your reg no longer delivering much air at 100' or 200'.

It might just mean that you are 68 with two bad rotator cuffs. Why I sling my pony.

 

[faze]

I appreciate all your comments and I completely understand your arguments.. so Is it safer to half turn close or leave fully open?