Why close the valve 1/4 or 1/2 turn???

[soudan]

OK, other than it is an old school thing, here is my 2 cents.

some times people do get confused (even though the famous Righty tighty lefty loosey exists in all our minds) but if your valve is either open all the way or closed all the way you might get confused! so a good way to clear that confusion is to have it a 1/4 closed, that way when you check your valve rotate it right rotate it left and if it stops rotating after a 1/4 rotation then its open, (that's why i do it).

but if you think your mistake free, then don't do it!

 

[wtxblaze]

I believe it has to do with the inner workings of the valve itself. We do the same thing with the valve on a oil well and its not so someone can come by later to check if its open. Everyone watches him open it and make sure he turns it back 1/4 turn.

 

[agilis]

I've never had or seen any scuba tank valves firmly jammed in the full open position, and even if this were to occur, it would be a post-dive issue, not a safety problem.

I treat every dive, even shallow currentless clear Caribbean dives, as if I were descending on the Andrea Doria. I check everything against a comprehensive mental check list. Then I do it again. And again. And once more. Watching your SPG as you take four or five breaths, and also as you manipulate the purge, before you even think about rolling off the side, is ultra-basic. So is turning the valve full on, off again, and back to full on, before you put the tank on your back. Checking regulator and gauge function, BC inflation and deflation, and the security of peripheral attachments are things as basic and as absolutely indispensable as a careful visual check for other divers before dropping yourself into the water. I don't touch a diving partner's equipment unless asked to, but I observe them carefully and expect the same.
If a divemaster or dive partner fools with my tank valve without my asking them to, I remove my gear and start my own check, from the beginning.

 

[Packhorse]

On occasion I have had DMs turn the air compleatly OFF then back ON. This screws with the connection between my computer (a vytec) and the pressure transducer, requireing that I recode the unit, and more time... I do complain about this. Its really a pain in the ****.

Surely this wouldnt matter unless the regs were purged after the valve was turned off.

I usually have mine full open and dont like anyone else touching it. If they do I always recheck.

 

[ianr33]

My valves are either fully open or fully closed.If open the reg breathes OK when tested pre dive.If closed you get maybe one breath then nothing.
If a reg is opened then backed off 1/4 turn there is a possibility that it will get closed and then opened 1/4 turn in error. This will breathe OK on the surface but will not have enough gas flow at depth. Happened to a buddy of mine in 60 feet of cold dark water.He no longer does the 1/4 turn back thing

As an aside,how many divers can reach the valve on a single tank? How many have no idea if they can reach it or not?

 

[beautybelow]

I've never had or seen any scuba tank valves firmly jammed in the full open position, and even if this were to occur, it would be a post-dive issue, not a safety problem.

I treat every dive, even shallow currentless clear Caribbean dives, as if I were descending on the Andrea Doria. I check everything against a comprehensive mental check list. Then I do it again. And again. And once more. Watching your SPG as you take four or five breaths, and also as you manipulate the purge, before you even think about rolling off the side, is ultra-basic. So is turning the valve full on, off again, and back to full on, before you put the tank on your back. Checking regulator and gauge function, BC inflation and deflation, and the security of peripheral attachments are things as basic and as absolutely indispensable as a careful visual check for other divers before dropping yourself into the water. I don't touch a diving partner's equipment unless asked to, but I observe them carefully and expect the same.
If a divemaster or dive partner fools with my tank valve without my asking them to, I remove my gear and start my own check, from the beginning.

I wish everyone who comes to do a recreational "vacation dive week" did the same thing as you....trust me there. But the fact of the matter is that in my experience, over half of the divers that I take diving are not like you. A lot of them do ask, most don't. Most of them had to be reminded how to put their gear (even perssonal and not rental) together. I think unless you have really dealt with the "general diving public", you may not have an idea of how many people go diving everyday with little experience or all that they have learned, forgotten. They certainly don't spend time on the internet learning about scuba diving, so most aren't reading this post. Like it or not, I am their buddy, the one that gets them in the water and back out safely. It's what I choose to do for a living, so I don't complain or talk down to them because they can't set up their gear or don't understand why they can't dive to 100 ft for 45 minutes even if they have the air left to do that. I just smile and say, yes, your air is on if they ask. If they don't ask, I have checked already and know for myself. It does make it easier if it is turned back a little to do a quick check, although I don't think that is why it is taught.

 

[beautybelow]

I can reach the valve...ugh...it's not easy though.

 

[beautybelow]

I've never had or seen any scuba tank valves firmly jammed in the full open position, and even if this were to occur, it would be a post-dive issue, not a safety problem.

I treat every dive, even shallow currentless clear Caribbean dives, as if I were descending on the Andrea Doria. I check everything against a comprehensive mental check list. Then I do it again. And again. And once more. Watching your SPG as you take four or five breaths, and also as you manipulate the purge, before you even think about rolling off the side, is ultra-basic. So is turning the valve full on, off again, and back to full on, before you put the tank on your back. Checking regulator and gauge function, BC inflation and deflation, and the security of peripheral attachments are things as basic and as absolutely indispensable as a careful visual check for other divers before dropping yourself into the water. I don't touch a diving partner's equipment unless asked to, but I observe them carefully and expect the same.
If a divemaster or dive partner fools with my tank valve without my asking them to, I remove my gear and start my own check, from the beginning.

by the way...I do understand your point of view, just trying to convey how it may be someone's business to check things like that.

 

[String]

Older valves also had a tendancy to seize on if fully opened and left there. One of my tanks with an old (10yr or so) valve did stick on in this way during a freeflow.

Probably not an issue these days so comes down to personal preference.

 

[1_T_Submariner]

Hi Manuel Welcome to scubaboard.
The Open a valve fully then 1/2 turn back is common practice on Submarines many valves are checked prior to submerging (by 2 people).
The problem with the valve being all the way open is to check it you would try to open it. The valve would not move you would think that the valve was open when in reality it was stuck shut. When the valve is opened all the way then turned 1/2 turn back you can very easily check it open then turn it 1/2 turn back. When checking a valve the safest way is check it open the turn back 1/2 turn, it really doesn't have much to do with the internal parts of the valve.
I understand everyone is responsible for their own gear this is just a good method to be able to verify the position of the valve.