Turning air off after equipment assembly

[Tigerman]

Go diving in Egypt in august and set up your gear and leave it pressurized on the boat ride out to the dive site and you'll see real clear why its suggested to turn off and purge..
You WILL blow o-rings under those conditions - but then again its beyond hot out there..

Your hoses and regs is not very likely to have any problems but o-rings is a different story. Especially yoke o-rings..

 

[t-mac]

Summary of posts so far for those of you just joining:

1. Leave the air on or off, but be consistent.
2. Leaving it on will not damage your reg (yeah!), but in really extreme conditions (Norwegians diving in Egypt!) you could blow an o-ring (bummer, but not generally a catastrophe).
3. By leaving it on you may detect a leak and you reduce the chances of diving with your valve off (not so good).
4. If you turn your air off, purge so you reduce the likelihood of sucking H2O (very bad day, indeed).
5. Do not omit pre-dive checks. Make sure your air is on before you plunge. Breathe your regs and watch your air pressure.

I think those are the high points.

So, what will I do in the future? Unless there is a compelling reason, going forward I will leave my air on until I dive. My reg doesn't leak air and it seems to me the most extreme inconvenience is that I will have to replace an o-ring, which I have to do about 25% of the time on a rental tank anyway! I always do predive checks and pre-breath my regs anyway and so this gives me the biggest safety margin balanced against the cost of a 5 cent o-ring and about 45 seconds of inconvenience changing it out.

In the relatively rare instance that I decide to turn my tank off, I will purge it, which is my normal routine anyway, along with a pre-dive check, and that way I achieve nearly the same safety margin.

Thanks for all the responses. This was very helpful for me and I hope it was for others as well.

 

[TSandM]

He replys, "I always turn it off, after I turn it on... and we've been diving so long, we don't need to do Pre-Dive safety checks anymore"...

Sigh . . .

 

[Ironman]

He replys, " ... and we've been diving so long, we don't need to do Pre-Dive safety checks anymore"...

Even duct tape won't help in that case.

I just smiled at him, shook my head and said, "Oh Really" ???

And, I am willing to bet he completely missed your point.

 

[GrumpyOldGuy]

I pressurize and leave off. Too many boat tanks have bad o-rings, I cannot hear a leak due to the surrounding noise and seeing the bubbles once I splash is too little, too late. Same for hoses, etc.. If the pressure drops on the SPG I know I have an issue and I have some time to address. Being off, there is zero chance of loosing air due to someone messing with my system or the purge getting pushed or a slow leak.

I suppose if I was in Egypt and dealing with brutal hot sun for long periods, I might depressurize after a a few minutes of watching the SPG to reduce O-ring issues, but that's an exception. The depressurization does not reduce the heat and you still going to hit that hot o-ring with 3000lbs when you do turn it on, more if the tank heated up in the sun.

Not matter what you do, never ever omit your pre-dive check. Once you walk away for your gear for even a second you risk some other diver or DM "helping" you and turning off your air. I am so paranoid I recheck once I am in the water, taking a breath while watching the SPG. More than once I have seen DM "check" valves on divers as they get ready to jump. They are trying to be helpful, but you can't see what they are doing and their error can be your end. If you are doing a negative entry, you do this right before you jump when you are in a position that no one can screw with you valves.

 

[RTee]

I normally set-up my block, turn the valve on, check gauge, inflator and regs and then turn it off.

I also had two instances of going down and after a breath or so sucking my regulator dry. One was of my own doing and the second one, the result of a well intentioned dispatching crew member who mishandled the valve. In both cases, I reached back and turn the tank back on.

Quite frankly, I think it does not really matter personal preferences of divers as long as you conduct a last minute check just as you are about to back roll, take a giant stride or simply deflate the BCD to start going down...ie take one or two breaths while watching your SPG. It will let you know.

I also don't pose judgement on individual who ask me to either turn their valve or ...to kindly remove the bungee cord so they can stand up. I think it has happened to most of us or it will as some point in time. Things will always happen on a boat, especially when folks are either pressured or feel pressured.

 

[Tigerman]

Its not about hitting the hot o-ring with 3000 psi, its about the fact that heat will make air expand, which again will increase the already high pressure..
An air AL80 can show 250-260 bar (3600 to 3800 psi) on the deck when you turn it on. If you submerge it for 10 minutes it'll drop to 200-210 bar (2900-3050 psi)..

Really, this IS a real issue if you go diving in Egypt and dive ops cover this in their "on the way to the jetty" information, yet it happens EVERY day that someones tank goes *POP*HIIIIZZZZZZZZZZZZZZZZZZZZZZZZ* because they forgot to depressurize

 

[kelemvor]

Don't you guys fill the bladder before jumping off a boat? If the air was off, wouldn't you notice the power inflator didn't work?

I was instructed air on, check your reg and octo. Check buddies reg and octo. Fill bladder, start breathing the reg before you enter and gitter done. Am I doing it wrong?

 

[fisheater]

Don't you guys fill the bladder before jumping off a boat? If the air was off, wouldn't you notice the power inflator didn't work?

I was instructed air on, check your reg and octo. Check buddies reg and octo. Fill bladder, start breathing the reg before you enter and gitter done. Am I doing it wrong?

Nope.


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[Tigerman]

Don't you guys fill the bladder before jumping off a boat? If the air was off, wouldn't you notice the power inflator didn't work?

I was instructed air on, check your reg and octo. Check buddies reg and octo. Fill bladder, start breathing the reg before you enter and gitter done. Am I doing it wrong?

I always test my regs by actually breathing them and watching the gauge and always fill some air in the bladder..

EXCEPT..
1. If youre doing a negative entry you wont fill the bladder as you want to hit the water and not come back to the surface untill the dive is over.
2. Im diving here at home and its gotten below freezing. At that point test breathing the regs on the surface only increase your risk of them freezing and freeflowing..
The 1st case I have only rarely done, the 2nd a lot more so..