Things Scuba Instructors teach that are either bad or just wrong.

[Wibble]

In a similar vein, have heard some rebreather divers say that they don't fully open their oxygen or diluent so that they can shut them down more quickly if there's a "boom!". Argument goes that you don't need to inject huge quantities of gas, so you don't need it fully open.

Seems logical.

But... some valves are slow opening, especially the AP valves which are very common in the UK. I've recently replaced an oxygen valve which requires two full turns before it even starts opening (yes, I need to get that looked at, but it eventually opens OK).

Personally I'm happier opening valves fully and then backing off a fraction of a turn; Mr Cockup doesn't come visiting.

At the end of the day, should the rebreather's oxygen or diluent go bang, then you'd probably be bailing out at least until you can work out what happened. Then see if it's a full bailout or some workaround such as offboard oxygen from the deco bailout or dil from the bottom bailout.

 

[boulderjohn]

In a similar vein, have heard some rebreather divers say that they don't fully open their oxygen or diluent so that they can shut them down more quickly if there's a "boom!"

Some technical divers on open circuit will leave valves partially closed so they can shut them down quickly if needed.

 

[inquis]

+1 on a bit off the stop, perhaps 1/16th of a turn or less? The slight movement prior to the stop is important feedback should I somehow happen to turn it the wrong way.

 

[scubaozy]

The quarter turn back when opening the valve on a tank. Still see it taught, drives me nuts. Outdated, irrelevant and dangerous!

Hehe, if you have seen as many beginners as I did, who are trying to turn on an open valve and turn off a closed valve..

 

[MarkA]

Hehe, if you have seen as many beginners as I did, who are trying to turn on an open valve and turn off a closed valve..

From what I remember. What you say about people not knowing on from off was the argument for either fully on or fully off.
Fully on = safe. You can breath
Fully off = safe. You can’t breath and don’t dive
On and back 1/4 turn = safe. You can breathe.
Off and back 1/4 turn = not safe. You may be able to breathe at the surface but not at depth.
Spent every day at work doing righty tighty, lefty loosey, so never understood people getting it wrong. But stuff happens.

 

[Bob DBF]

Am very happy that the valve is turned on then backed off a bit; I probably use about 1/8th of a turn, but not hard against the end-stop as metal contracts when it's cold.

The concept is to never backseat a valve that is not built for that purpose as it may jam open. The 1/4 turn is teaching by catchphrase, rather than giving a student an understanding of the reason. Back when post valves took forever to open that could be a good rule, now that avalve can be open in two turns, or less, a 1/4 turn is a much greater distance. So with 1/4 turn open on a modern valve you can breathe normally to 30', or better, but with a post valve you probably will have restricted breathing on the surface. I'll have to check on that next time I get a chance.

 

[BoltSnap]

I avoid taking medications without prescription.

You must be eating a lot of garlic...

 

[scubaozy]

From what I remember. What you say about people not knowing on from off was the argument for either fully on or fully off.
Fully on = safe. You can breath
Fully off = safe. You can’t breath and don’t dive
On and back 1/4 turn = safe. You can breathe.
Off and back 1/4 turn = not safe. You may be able to breathe at the surface but not at depth.
Spent every day at work doing righty tighty, lefty loosey, so never understood people getting it wrong. But stuff happens.

I am not arguing, just telling what I see, a 200lbs fit male diver trying to force open and open valve will not do good on that valve. Just recently, on a rib dive, I had to interfere an experienced diver shutting down a valve because the buddy asked to turn it open. This is just a minute before a negative entry. You can be sure on how you handle your valve but someone asks you to turn on their valve on and the valve is actually on, your righty tighy will likely fail due pov. It takes a lot of repetition to handle others' valves in different configs to be able to identify correct direction without thinking. So it is debatable what is more dangerous, turning the valve little back so that you can right away identify on/off or risking poor air delivery. My own rule is turn back of tiny bit so that you can move the valve with index finger and thumb, I guess this is roughly 1/16 turn. I see your point about the last case but remember, when you turn on the valve first time, you will get positive feedback and if you applied the rule, turning it on and than back it is hard to get it wrong.

 

[Angelo Farina]

You must be eating a lot of garlic...

No, unfortunately I need Valsartan for blood pressure, plus a number of other drugs. All under medical prescription.
My point is exactly avoiding DIY medications.
My body is in a too delicate equilibrium for risking to mess it up assuming substances with significant medical effect without control from my doctor.
So no garlic, no oxygen, etc.

 

[BoltSnap]

no garlic

That's tough, food without taste