Full on, and a little off

[Bob DBF]

Your question was answered. In the early days, we were taught to open the valve fully, then back it off a hair (but not a quarter turn). This is what I was taught when I started diving in 1976, and was told we did this to prevent the valve from getting stuck in the open position... FYI, 1/4 turn is quite a lot, actually way too much. Tank valve do not require very many turns to open or close fully... if you feel the need to back them off, just a tiny "smidge" is enough.

I was taught to back it off a "smidge" as well, to insure it is not backseated. It was even more important when SPG's came into use, because you can see a deflection with an air check if it is only open a smidge but you will not see a deflection if opened a 1/4 turn.

As you mentioned, if anyone is mechanically challenged, all bets are off anyway.



Bob

 

[azhar]

The article above is "cave diver harry's" own argument ... not an industry norm .....Not quarter but slight final twist is fine ... prevents valve from jamming... if the needle fluctuates while breathing, it could be multiple reasons ... valve closed or blocked ... reg filter blocked ... reg first stage not performing ... reg first stage piston jammed or not adjusted properly ... so it can be many factors or a combination of them. Needle fluctuation on surface is a big no because it means that the "system" can not deliver enough air on surface or its delivering too much air on surface ... not enough air will make you out of breath while too much air will burst your lungs.

 

[Hickdive]

Great article. For a years I've been teaching the fully turned open but quarter turn back to minimize galvanic action on the valve.

Galvanic action on the valve? What Galvanic action and why would a quarter turn prevent it?

Valve spindles are chromed brass, valve bodies are chromed brass, HP seats are brass-bodied with a nylon face or all nylon, o-rings are buna or viton, lubricants are silicon grease or chrystolube, rings are nylon, handwheel is plastic or rubber, handwheel bush is nylon, spring is stainless steel, bonnet is nylon/brass or chromed brass.

I am genuinely fascinated because this is something I've never heard of let alone encountered.

 

[markmud]

Galvanic action on the valve? What Galvanic action and why would a quarter turn prevent it?

Valve spindles are chromed brass, valve bodies are chromed brass, HP seats are brass-bodied with a nylon face or all nylon, o-rings are buna or viton, lubricants are silicon grease or chrystolube, rings are nylon, handwheel is plastic or rubber, handwheel bush is nylon, spring is stainless steel, bonnet is nylon/brass or chromed brass.

I am genuinely fascinated because this is something I've never heard of let alone encountered.

Hello Hickdive,

It was common practice on vessels to jam open or closed all through-hull seacock valves. This was to prevent electrolytic action against the valve stem and gate. If the valve was locked, one way or the other, a good electrical connection was made which allowed the bonding system to transmit any stray current to the sacrificial anode (zinc).

All metals on vessels are supposed to be similar. Not dissimilar. Dissimilar metal corrosion is different from electrolytic action. They are both considered galvanic action, but they are caused by different means.

A valve in the partially open, or partially closed position, will not prevent galvanic action, whether it is dissimilar metal corrosion or electrolytic corrosion.

I agree with you, what was that poster writing about? Especially since SCUBA gear is in the water for short periods of time, neither form of galvanic corrosion would be consequential.

True brass is not a marine underwater metal. Brass is an alloy of copper and zinc. Zinc is a sacrificial anode. Toben and silicon bronze are excellent marine metals (neophytes sometimes refer to them as brass). Brass is subject to immediate electrolytic action because the zinc is leached-out vary quickly. A professional mariner should always make a distinction between brass and bronzes. Brass bad--bronze good.

markm

 

[Hickdive]

Hello Hickdive,

It was common practice on vessels to jam open or closed all through-hull seacock valves. This was to prevent electrolytic action against the valve stem and gate. If the valve was locked, one way or the other, a good electrical connection was made which allowed the bonding system to transmit any stray current to the sacrificial anode (zinc).

All metals on vessels are supposed to be similar. Not dissimilar. Dissimilar metal corrosion is different from electrolytic action. They are both considered galvanic action, but they are caused by different means.

A valve in the partially open, or partially closed position, will not prevent galvanic action, whether it is dissimilar metal corrosion or electrolytic corrosion.

I agree with you, what was that poster writing about? Especially since SCUBA gear is in the water for short periods of time, neither form of galvanic corrosion would be consequential.

True brass is not a marine underwater metal. Brass is an alloy of copper and zinc. Zinc is a sacrificial anode. Toben and silicon bronze are excellent marine metals (neophytes sometimes refer to them as brass). Brass is subject to immediate electrolytic action because the zinc is leached-out vary quickly. A professional mariner should always make a distinction between brass and bronzes. Brass bad--bronze good.

markm

I've no doubt you are correct with regard to valves on ships; however, the poster who described this as a reason for a turn back was referring to scuba cylinder valves, hence my question.

 

[gypsyjim]

I too was originally taught to open the valve, and then back off a 1/4 turn. (supposedly to save the valve from abuse, and i blindly accepted that reasoning, even having reason to know better)

Later I was taught in Rescue, and in a Fundies class to turn a valve on, or off, all the way. That way you know exactly which it is just by reaching it, and seeing which way it turns. No guesswork involved. No chance of getting into a situation where the valve is not opened far enough to deliver the needed gas at depth, which has killed a few divers over the years.

Since as a jeweler I use gas valves daily, I know from experience that opening a valve completely, repeatedly, ever day of the week will not damage it in any way, if you do not over twist it. We use tanks with valves that have been in rental use daily for decades, and they still function, which is far more use than most typical scuba tank valves will get, except in extreme rental situations

I have since adopted the all open, or all closed approach to my scuba diving. Again, I can reach over my shoulder, and in an instant assure that my gas supply is full open, and never worry if it is open far enough.

 

[FinnMom]

Thanks GRF88... that was the article that prompted this thread - I'm more than familiar with it - my original question stands

Quoting the article:
"Make sure your valves are either all the way open, or all the way closed"

No 1/4 anything. You could say it's an open & shut case

 

[mala]

if its closed then 1 turn will give you gas pressure.
if its fully open and you want it closed it will take quite a few turns.

just saying.

 

[Lost down under]

if its closed then 1 turn will give you gas pressure.
if its fully open and you want it closed it will take quite a few turns.

just saying.

A 1/4 turn back is hardly going to make a difference in terms of turning the tank off.

 

[Glenn08]

Always turn valves (scuba tank valves included) all the way on, and then back 1/4 turn - but there are exceptions. Acetylene tank valves are never turned fully open. Throttling, needle, and other flow control valves are only partially opened to the required setting. There are many techniques that are normal to tradesmen, but not appreciated by others. Not turning valves fully open apparently is one. A tangent - apparently 'blunting' a nail is also a mystery to many people.