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Tanks on - half turn back or not?


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#16 peterbj7

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Posted 12 June 2009 - 03:11 PM

I used to own 500 tanks and have never experienced a stuck valve with those tanks. Broken or defective vales yes, occasionally, but never one simply stuck so it won't turn. I have, however, experienced that with tanks from a rival operator that give all appearances of not being so well maintained. Once I was with a group using such rented tanks and two couldn't be shut down once back on the boat. Meant we had to purge the tanks via the regulators until they were empty and the regs could be removed - took a long time.

My practice & teaching has always been to open the valve fully, then back off a little (not as much as half a turn), then breathe the reg and make sure the gauge doesn't move. As "just a diver" elsewhere I have several times had boat staff meddle with my tank while I'm on my way to leave the boat, which is why I always breathe the reg and watch the gauge for movement immediately before leaving the boat.

It's a good basic skill for all divers to be able to reach and turn their tank valves underwater. It's taught at tech level but needs to be part of every diver's skillset.

#17 Dive_Girl

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Posted 12 June 2009 - 03:56 PM

It's a good basic skill for all divers to be able to reach and turn their tank valves underwater. It's taught at tech level but needs to be part of every diver's skillset.

I think this is great advice and something all divers should try their next dive out. Can you reach your own valve underwater?
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#18 scubaski

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Posted 12 June 2009 - 05:44 PM

Not fexible enough to reach my tank valve unless I slide off bc. I turn valve full open then close 1/4 turn.
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#19 peterbj7

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Posted 12 June 2009 - 09:15 PM

For some months I couldn't reach back there with my right hand as I had a problem with my shoulder, so I learned to hold the bottom of the tank up with the right hand so I could reach across with my left. Clumsy but worked. I'm now back to being able to do it with my right hand.

But if on any particular occasion you need to get out of the rig to do it then that's what you should do. How many divers are comfortable with the idea of taking their scuba unit off underwater? How about when not sitting on the bottom? - suppose you have a problem while diving a wall. Another vital for the skill set.

Anything that you would expect a buddy to help you with you should learn to do for yourself.

#20 ScubaDadMiami

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Posted 12 June 2009 - 11:30 PM

I turn my valves fully on and leave them on. You might think that it will be easy to remember which way to turn the valve until you are faced with high pressure emergency situation. You would be surprised at how quickly "logic" disappears in such a circumstance (which is one of the reasons to practice skills until one doesn't have to think about them but can instead perform instantly). Also, when you start adding more valves, this can complicate things further. So, start off with one valve, and use that same practice when you move up to more. There is no confusion between a valve that is on or off if it is all the way on or all the way off no matter how many valves there are.

I instruct all diving staff of a boat not to touch my equipment or valves (though I appreciate it when they will hook up a sidemount tank or will let me pass up my open circuit tanks from the water). So, I have no risk of someone being "helpful," resulting in turning off my gas flow. Problem eliminated.

The worst that will happen with a valve that is stuck open is that you will have to purge the regulator to empty the tank. (There is also the potential for a lost gas scenario if both a free flow and a stuck valve happen at the same time. However, consider the odds of that happening before taking precautions against that scenario over much more likely scenarios.) Typically, the worst that can happen with a tank valve that is accidentally turned off is an unnecessary gas share or worse, a very bad ending. I am willing to risk the tank purge more than I am willing to risk the bad ending.

I concur with Jim's theory about the cause of valves sticking open. I would only add to that that you do not have to open the valve forcefully against the fully open position. Just have it lightly and barely resting against the fully on position.

I maintain valves on a daily basis, sometimes half a dozen per day. You won't find problems with a properly maintained valve sticking open. So, maintain your valves properly, open them all the way, and don't worry about it. Enjoy your dive.
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#21 JimG

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Posted 13 June 2009 - 07:56 AM

Not fexible enough to reach my tank valve unless I slide off bc. I turn valve full open then close 1/4 turn.

Not questioning the lack of flexibility, but sometimes people have trouble reaching the valve because they are using a sub-optimal technique.

What I do is extend ny right arm straight out in front of me, and then go straight back over my right shoulder, such that the inside of my elbow brushes the right side of my head as it goes by (that's a bit of an exaggeration, but it's the only way I can think of to describe the motion). Doing this without tanks, I can touch a point well below my shoulder blades, almost in the middle my back. A lot of people try to reach the valve from the side, which does not give nearly as much range of motion as reaching from the front.

The other trick is to make sure you are horizontal or even slightly head down in the water. If there is any air in the BC, then from that position it will migrate to the back, which will raise the cylinder off your hips a little, while pushing it towards your head. Only your arm should move when you do this. People sometimes have a tendency to rear back, which makes the skill much more difficult to do. If you are head up, then the air in the BC will rush to the shoulders, pushing the cylinder valve farther from your head (and making it harder to reach).

Try it and see!

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#22 Landlocked Dive Nut

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Posted 13 June 2009 - 08:50 AM

How many divers are comfortable with the idea of taking their scuba unit off underwater? How about when not sitting on the bottom? - suppose you have a problem while diving a wall. Another vital for the skill set.


I'm pretty sure we're all taught how to do this on the bottom during OW training. I was only recently shown a good way to do this while suspended in the water column (with weight-integrated BC.....a much trickier task than if you wear a weight belt!). I have practiced it in the pool, but not in open water yet.

Come to think of it, removing gear in open water is a skill set that I have NEVER seen being practiced by anyone on any recreational dive trip. Since it requires more thought than typical recreational diving skill sets, I'm sure the stress of an emergency situation will affect the performance of this skill, particularly suspended in the water column.

But if you cannot reach your valves when you need to, either due to a lack of flexibility or the position of your tank, this is a skill set that you need to practice once in a while.
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#23 peterbj7

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Posted 13 June 2009 - 09:20 AM

I instruct all diving staff of a boat not to touch my equipment or valves ..... Problem eliminated

Would that were true!!


I turn my valves fully on and leave them on

Including your manifold valve?

#24 ScubaDadMiami

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Posted 13 June 2009 - 02:36 PM

Including your manifold valve?


If you are talking about open circuit here, yes, I would leave the center post open on a manifolded set of doubles. Wouldn't you?

Is "manifold" the King's/Queen's English for the CCR tank first stage connection? On CCR, I just turn the O2 side on as far as I can turn off in a single twist of the wrist. On the Dil side, I'll go a bit more.

The CCR situation is different because the tanks are so small that even a small gas leak can drain all gas in a few seconds. Therefore, there is emphasis placed on turning on and off valves from this position from day one. For example, shutting down and feathering the tank valves while breathing is a required skill with most CCRs.

On the other hand, for my open circuit bail out tanks, I turn the valves fully on. I installed shut-off valves just before the second stages. That way, I can prevent gas leaks from the second stage when gas isn't needed, and I can have full-on gas available at the flip of a switch.
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#25 JimG

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Posted 13 June 2009 - 08:33 PM

If you are talking about open circuit here, yes, I would leave the center post open on a manifolded set of doubles. Wouldn't you?

I know I do!

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#26 techintime

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Posted 13 June 2009 - 09:12 PM

I'm a full on then 1/4 turn back guy as well. The rationale as I understand it (and it makes sense to me) is that if a diver were to turn a tank fully on (with no back turn) and then along comes his dive budy or dive master to check that the tank is on, the second person may trying to turn it on (when in fact it is already on) and thinking that it is just a sticky knob or turned off really tight, he may really crank on it and damage the valve. But if it were backed off a quarter turn, the second person would easily realize that that the tank was already on by the quarter turn of movement and not make the mistake of really cranking on it.
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#27 ASDmike

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Posted 14 June 2009 - 07:03 AM

... if a diver were to turn a tank fully on (with no back turn) and then along comes his dive budy or dive master to check that the tank is on, the second person may trying to turn it on (when in fact it is already on) and thinking that it is just a sticky knob or turned off really tight, he may really crank on it and damage the valve. But if it were backed off a quarter turn, the second person would easily realize that that the tank was already on by the quarter turn of movement and not make the mistake of really cranking on it.

Coming up on twenty years now, so I was having a tough time remembering what my late great YMCA instructor told me... He covered a lot of practical info knowing most of his OW students jumped into the "diverse" world of resort diving that was the late 80s/early 90s. Probably said much like techintime above and also that before we hit the water, we will have had our air checked 3x by others. And any one of the helpful checkers might have a harebrained moment and turn a fully open tank, fully closed. The quarter turn thing was to prevent the valve from being over torqued and as a mental reminder of which way to turn the valve to open it. If one of the helpers is not sure 100% which way to turn to open a valve they will be "feeling" if the valve is on a stop and if it is, they will turn it fully the other way. Which is of course bad news if it was fully open. The beauty of the 1/4 turn was those checkers should be looking for it. A 1/4 turn open to the stop and back the 1/4 turn is a quick 1 second check that had a great chance of being done right every time. Being presented with a fully open valve takes a lot longer for either a Club Med GO or GM to figure out at that first 8AM dive after being in the disco till 4AM. :) :) :wub: :lmao: :elf: :teeth: :lmao: :wow: :taz:

BTW, it has not always helped. I have had at least two tanks turned off accidentally by helpers just before I hit the water. I knew it had been open, checked and double checked, yet I'm twisting around in the water to open my valve.

:)

Or at least they said it was an accident....

:D


That was the big reason after you are cleared to enter the pool to draw a breath and watch that needle not move. My I agree with those that are always in 100% control of their gear and turn the valve fully open. On trips when I know I am not going to be "helped", I don't bring the valve back that 1/4 turn.
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#28 Keith B

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Posted 17 June 2009 - 09:09 PM

... My buddy could not understand why I was showing him my pressure gauge with needle swinging every time I breathed in as I was pointing to my back....


My O/W instructor used to make us check our SPGs just before submerging by taking a few deep breaths from the reg and watching the needle "If it moves by just a mozzie's bollock (US translation: the width of a male mosquito's testicle), check your bloody tank valve", he used to say.

Caveat: This advice WAS given back in the dim and distant past, before the advent of single hose regulators, but I still use it today -- old habits die hard.

#29 peterbj7

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Posted 17 June 2009 - 11:20 PM

Including your manifold valve?

If you are talking about open circuit here, yes, I would leave the center post open on a manifolded set of doubles. Wouldn't you?


Yes, but only just. Unlike a valve you're breathing from it only needs to be barely open to do its job of equalising the tank pressures.

#30 JimG

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Posted 18 June 2009 - 04:06 AM

Unlike a valve you're breathing from [the isolator] only needs to be barely open to do its job of equalising the tank pressures.

That may be true, but I don't consider that a good practice for overhead environments. "Full on" is the accepted method in cave diving, from what I was taught (and have seen).

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