Diving Myths #2: Turning the tank valve a quarter turn back.

This is another one of those techniques that we’ve all taught as instructors because we’re just copying what our instructors told us. I’m not aware of it being mentioned in any of the PADI materials. I certainly used to do it myself under some vague comprehension that doing so meant that the valve wouldn’t stick open. This was despite having never seen a valve stuck open up to that point or since I started teaching students to open the valve all the way.

1st stage

A 1st stage that isn’t stuck to a tank. Probably because it’s awesome.

The turning point for me came when I started tec diving where you turn your valves all the way open or closed (there’s a story in there somewhere but not for this blog. Ask me down the pub). Anyway it occurred to me that the valves we used in tec were just the same as the ones in recreational so what was different? Had a magical valve pixie appeared and sprinkled his enchanted dust of non-valve stickiness over tanks that were used for tec? Or was it, as I suspected, complete bollocks?

I started to ask about a bit and discovered that most instructors teach this technique. In the UK, no one had seen a tank valve stick open. However overseas some instructors where aware of this happening but that it really just meant that you needed a bit of extra oomph to close it. It certainly wasn’t a servicing job.

So it seems to be a technique born out of experience based on either poor quality valves or ones where regular servicing may not always be so regular. The quality of valves on cylinders in the UK is usually very good and as I mentioned at the start I have never seen or heard from anyone else of one sticking open. Therefore I suggest that you teach your students to open the valve all the way.

I’ll explain why: Closing a valve a quarter or half turn back is potentially very dangerous. If you are about to enter the water and suddenly think that your air needs to be switched on, you might ask your buddy to do it for you (I’m aware there are ways to check these things but if everyone did every check then there wouldn’t be any accidents caused by missing them). If your buddy isn’t sure they might end up switching your air off and then opening the valve a half turn back. This has the effect of allowing air into the regulator and allows you to breathe. Your gas may then cut off at depth when the pressure in the tank drops below a point where it can hold the valve open.

Whilst this is unlikely, it’s completely avoidable by having gas all on or all off. That’s why we do it that way in tec so as to avoid any confusion.

So forget about all this quarter turn back business and teach your students to open the valve all the way. Then you’ll look like the cool new instructor on the block, swaggering in with your attitude and new fangled ways that the old hands will at first distrust but then in a series of unlikely events, mainly caused by someone doing that thing the old way, you’ll step in, save the day and in return earn the grudging respect of the towns folk. That may also be the plot of most 80s movies starring Michael J Fox.

Next time we’ll be tackling the thorny scuba related issue of how much of the music of Phil Collins is too much? (Preview answer: A lot).

Postscript: Since putting this up there’s been quite a few people taking issue. A mate of mine pointed me in the direction of this link which I think helps add a little weight to the argument. Thanks Paul Flower!



14 thoughts on “Diving Myths #2: Turning the tank valve a quarter turn back.

  1. Olav says:

    We teach the quarter back turn in rec diving.
    BUT it is not to avoid the valve stuck open. It is to avoid the valve to be damaged by being closed to tight.

    If one follow this procedure with the quarter back turn.
    If a diver finds a valve stuck, it should mean, that the th valve is closed.
    If a diver finds a valve loose (by the quarter back turn), the valve is nearly fully open and the diver can manipulate the valve as wanted.

    BUT if, as suggsted in the original article, the diver turns the valve completely open to the more or less stuck position. And later the diver or buddy can’t remember, if the valve is completely open or closed and turns the valve to closed position but the valve already was closed, the teflon vlave part will be damaged leading at the end to at leaking valve, that can’t be closed.

      • So it would seem that the damage is caused by the valve being over tightened whether it is closed or opened?

        I’d be interested to know what types of valves you use, as it never seems to happen in the UK. I’ve been teaching all my students and instructor candidates to do this for some time and the only place I’ve heard of there being an issue was in Malaysia.

        I do understand that there is a potential problem with valves getting stuck but reports of actual damage to the valve seem to be pretty rare. In the same way we teach student divers to seal a regulator hand tight, we can teach them to open a valve all the way without over tightening. Every now and then someone will always screw a DIN regulator into a tank with enough force to make the reg and valve fuse together forever(!) and someone will always over tighten a tank valve, it’s just one of those things.

        I still believe that the safety reason not to turn the valve a quarter turn back out weight potential wear and tear issues on kit but in fairness the article was mainly aimed at UK based instructors where there doesn’t seem to be an issue.

    • some random tec instructor says:

      or you could just teach people how to look after their valves. you shouldn’t ever need to use excessive force when opening or closing a valve. You should be able to open and close a properly serviced valve with no more force than finger and thumb, if it needs force service it simple. Also as a side note how do you do your s drills with valves at quarter turn? There is evidence that having valves half/quarter turn back has been a contributing factor in accidents which to me is not acceptable, especially when servicing a valve is so incredibly simple.

  2. Tom Nomad Diver says:

    Completely agree with Olav.
    There is as well a big difference between rec and tec and that’s the buddy check. In tec the diver is merely self responsible or his equipment and should be very well aware if his valves are open or closed. In recreational diving the open valve position check is an essential part of the buddy check.
    Somehow the new instructor appears maybe as a very cool guy with all his tekkie background to the student, but messing around with a standard procedure safety check might have some disadvantages on the safety later!
    It was btw mentioned in the old PADI OWD video / chapter one..
    A good thing to teach to students is to look at the pressure gauge when they breath from the reg, if the needle is moving something is wrong and your buddy might closed your tank and opened it only a quarter.
    The complete open valve procedure was invented by the technical diving legend Sheck Exley,
    Look it up in the “Blueprint of Survival” if you can get a copy of it.
    Kind of the first ever Technical Diving / Cave Diving Manual. Makes a lot of sense in technical diving but wasn’t meant for beginner recreational divers.

    • Thanks for the comments! What is the reason for teaching an open water diver to turn the valve back if a tec diver is allowed to open them all the way? I’m also not quite sure what the argument is that teaching recreational divers to open a valve all the way is unsafe?

      I understand the value of teaching them to observe fluctuations on the SPG, but I have seen valves closed and reopened a half turn that do not cause SPG fluctuations on inhalation. If the valve is either open or closed the fluctuation will be immediate and apparent.

      As far as I can see the arguments weigh up as follows:

      1. Opening the valve and turning it back:

      Advantage: No chance the valve will stick open (or closed if they do it the wrong way).

      Disadvantage: Small possibility that the diver will enter the water with their valve closed and reopened a small amount leading to gas supply cutting out during the dive

      2. Opening the valve all the way:

      Advantage: No chance of diver entering water with gas supply only partially turned on.

      Disadvantage: Small possibility of tank valve getting stuck.

      I personally have never seen a tank valve get stuck in 13 years of diving including running a London dive centre (although I know that doesn’t mean it doesn’t happen- maybe you guys have seen it happen a lot)?

      So when you look at the pros and cons, I don’t see how you can conclude that turning the valve back is a better option. I think that we would be better teaching students to open valves all the way and then if they dive somewhere that is a problem then the dive centre can brief them about the quarter turn as a local protocol.

  3. It was interesting to read the article and the comments. I see all kind of reasons divers and instructors do a fully open plus quarter turn back but, since I started teaching cave divers, it took a whole new meaning, included to me.
    Whatever configuration a diver uses, in the event of a free flow for example or dislodged first stage (not placed properly in first place), the diver in difficulty is taught to self rescue first and then if he/she can’t solve the issue, ask to the closest team member.
    One thing is for sure, at least in my mind now, is that, if valve is fully open, the diver in difficulty has only one option – CLOSE the valve.
    In overhead (cave and or wreck) what gives us time to solve a problem is gas and the more we loose gas, the less we have time…
    So, as far as I am concerned, my student divers, from OW to stage sidemount cave, they are on the same page. OW divers are not taught self-rescue.
    What are your thoughts?

  4. This is an issue that had never occurred to me until this incident came to light on an actual dive.

    Like the rest of the PADI fellowship, I’d followed the rule and advised, with full conviction, all-the-way-on-quarter-turn-back… with an I’m-awesome-me “And here’s why, kids…..”

    Invariably, though, I’ve seen this cause confusion on bustling dive boats. Multiple DMs, harried buddy checks and peer pressure… ‘Can you turn me on?’ or ‘Am I on?’ etc can always be heard pre-stride, coupled with over-eager DMs randomly twisting/checking tank valves on the dive deck. Setting up your own kit, hurtling through your 34th buddy check of the week gives no guarantees. Buddy checks are all well and good; checking air, checking gauge, divers following procedures no matter what their experiences, but I for one have hit the water minus weights or an open zip on the dry suit… and without gloves in ice cold water, for which I won a very prestigious award (thanks x). Shit (can and will) happens.

    Do buddy checks work? Of course. Are they fool-proof? Not at all. Most experienced divers are guilty of skipping procedures, or rushing off the deck to grab the shot-line or a pod of ocras (as if..!). Then there’s the fresh new Open Waters bobbing about on their first live-aboard, out of sight and out of mind of the institution that reminded them Bruce Willis Releases Awful Films. B-W-what?

    With all the helping hands, all the bustle (and pressure) and no last ‘let me just check myself to make sure’, the one sure thing we can rely on… when I descend, can I breathe..? Reg-in, breath, OK, descend. No last double-check, no last glance at gauge… all good… right? The idea that a buoyancy-deficent, cycle-kicking newbie bumbling their way down to 18m to meet with the no-air-pinch of fate is terrifying. Where’s Bruce Willis when you need him?

    The argument is pretty simple for me. Forget tradition, what we were first introduced to and buddy checks… how can I ensure this incident never happens? All on, all off. Done.

    Valves get turned all the way on and all the way off every single dive… I fail to see how a second light twist of the valve would lead to premature valve failure, unless you’re buddied-up with Bruce Banner in a decidedly colourful mood. That being said, if you’re worried about your valves, don’t touch it… take a swig of gas. If it’s all ON or all OFF, you’ll soon get your answer. I sure as hell don’t want to be sat enjoying the view from a chopper air-lifting some kid to a chamber saying ‘Well, at least my teflon valve is still in tip-top condition’.

    Great post… Definitely food for thought, and most definitely room for much consideration.

    Dive safe x

  5. As I understand it the half turn back is as much for the divemasters benefit. Last thing our divemaster does when assisting the diver to enter the water is check the air is on by giving a half turn to fully open, then half turn back again. S/he is already holding the tank to steady the diver as they approach the edge of the boat to step off, so its a quick easy movement. If the tank valve doesn’t move then that usually means the air is off so they then turn it on. If someone has broken convention and turned the tank all the way on (a very rare occurrence) the divemaster usually ends up further tightening the fully open valve, and delays the divers entry while figuring out what is wrong.
    From a clean slate fully open may be the better choice, but changing the established convention will cause problems that in no way justify the benefits….

  6. Hi guys, thanks for all the comments, a couple had gone into spam and I accidentally think I deleted one, so if you don’t see your post then please do repost, I’m not trying to censor you! I’m on my brothers stag do at the moment so will reply to some of the posts next week. Thanks again.

  7. missy says:

    Let me share my boyfriend’s experience with you…

    When night diving in Egypt, with only his Lycra overall on (30 °C ‘n’ all), the string of the Lycra overall got wrapped aroung his valve and as he was moving his body during the dive the string was slowly tightening the valve. All of a sudden his air supply was cut off. He flash-light signaled his team member, she swam to him, held him as the other two divers that were near by at that moment opened his valve. He said he wasn’t even aware that there were any other divers around. He looked at her strangely as she was only holding him and just looking at him, not helping in the first couple of moments. :))) But a few seconds later he felt someone moving his tank, opening the valve.

    You must be aware that it was a situation involving experienced divers. It all happened in half of a minute, because his fellow divers had a lot of diving experience. What if that hadn’t been the case?

    The valves are all the way open for us since.

  8. Lars Monsen says:

    Maybe you should discuss this with you training agency first. And my all means; do talk to someone who can teach you a bit about valves and regulators – “only happens in malaysia”, hahaha…

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