Why isn't there a tank valve-open marking?

[Patoux01]

Fact: Many people are told to open the valve fully and back off a quarter turn.
Fact: Too many people don't know how to open or close a valve (cf OP post, and the fact that there's always someone trying to close my tank).
Fact: Many people believe that if the SPG needle doesn't move when breathing, your valve is fully (or minus a quarter turn) on, therefore you'd catch any mistake.

Well, the last one is just wrong. Which means that if some moron (sometimes yourself) closed your valve and backed off a quarter turn (ie your valve is open only 1/4 turn, YES THAT IS A MISTAKE, WE KNOW, PEOPLE TRY TO DETECT THAT MISTAKE), you will not detect it by "breathing hard in your reg on the surface", and you will jump in with a closed valve if you don't check it by hand (not including vindicators).


Oh, and by the way, both Dan T and myself are fully aware that you can breathe with no problem on a fully open (even minus half a turn!) valve. But you have to understand what the mistake is that I am trying to prevent by warning against that quarter turn before trying to send your CV.

 

[Dan]

There is absolutely nothing gained in air flow by leaving it against the stop except in the mind of the user.

Forty six years diving with over 2050 dives in addition to 20+ years using high pressure gas cylinders in an industrial setting proving the above statement to be correct. I've made dives to over 150FSW with my valves backed off the stop a degree or 3 with no ill effects. I don't do experiments, I'm not a scientist, I live in the real world where what works is the way to I do things. I do invite you to do whatever works for you.

I just cringe every time someone posts this 1/4 to 1/2 turn nonsense that is not correct and I agree could be dangerous in some situations.

Full open or full open with back off a degree or 3, as you see in the previous valve curve, would make no difference. It's still I consider them wide wide open. The danger is to have fully closed with back off 1/4 or 1/2 turn nonsense as you mentioned. The latter simply means the valve is closed in my book.

"Some" of the newbies just confused on which way to turn on the valve, as if they never turn on the faucet at home.

 

[Diverman68]

Open it all the way.JUST DON'T JAM IT.

 

[diver0008]

I often see some bubbles leak though the bad tank o-ring that created high air usage. I get the habit of not only checking the tank pressure, but also listening any hissing sound coming from the reg before doning on the gear.

Agree 100%

An excellent step towards ensuring a maximized diving experience.

 

[lermontov]

I'm wondering if you guys are dense...

Fact: Many people are told to open the valve fully and back off a quarter turn.
Fact: Too many people don't know how to open or close a valve (cf OP post, and the fact that there's always someone trying to close my tank).
Fact: Many people believe that if the SPG needle doesn't move when breathing, your valve is fully (or minus a quarter turn) on, therefore you'd catch any mistake.

Well, the last one is just wrong. Which means that if some moron (sometimes yourself) closed your valve and backed off a quarter turn (ie your valve is open only 1/4 turn, YES THAT IS A MISTAKE, WE KNOW, PEOPLE TRY TO DETECT THAT MISTAKE), you will not detect it by "breathing hard in your reg on the surface", and you will jump in with a closed valve if you don't check it by hand (not including vindicators).


Oh, and by the way, both Dan T and myself are fully aware that you can breathe with no problem on a fully open (even minus half a turn!) valve. But you have to understand what the mistake is that I am trying to prevent by warning against that quarter turn before trying to send your CV.

Fact #3 - your quite right at surface the needle will not perceptibly move on a 2 quick breathes check ( if valve closed and opened ¼ turn) but drop down to 3ATA and suddenly u realise theres a problem
Its a simple solution to get a system in place that you do every dive check(and be anal about it) so theres no mistakes. Valves fully open or fully closed -purge reg until your 100% confidant its either open tor closed

 

[diver0008]

My tests show exactly why the quarter turn kills

It's not the quarter turn that kills, but not knowing how to open a tank valve that may. As long as the valve is open before the small adjustment, no harm is done. Which brings us back to the OP's idea of having arrows to indicate which way is open.

 

[RainPilot]

A quarter turn on maybe... Not fully on and backing off a quarter

I've never ever had a DM or anyone mess with my tanks when on, if they did I'd feel it. But then I don't go on full service nanny boats

The only time I have nearly entered the water with a valve off is because I've turned it off again for some reason. My check have caught it, even if they didn't which just atmospheric pressure in my wing I stay at the surface (yup rolled without adding air too)

I am the reason that there is no such thing as idiot proof

The point is not that a small turn back is dangerous. It isn't. The problem is that if it's the other way round with valve closed and a bit back, that can become life threatening.
I have no reason at all to turn the valve back a bit, what's the worst that can happen? The tank stays open after the dive, I empty the tank and service the valve. I'm ok with that.

Edit : Hit reply and missed all the other comments similar to mine. Oops.

 

[Bob DBF]

One can argue that "the needle is moving!", but noticing it with the sun on your spg and on a rocking boat? I know I wouldn't.

First of all you should notice you are going on a dive with 50 bar in your tank! Joking aside, you will find a different result with a full tank, the higher pressure will drop will deflect the needle more with the same restriction than a lower pressure.



Bob