Out of air incident.

[Dan]

No, you have it backwards. It's the pressure downstream of the 1st stage regulator that CLOSES the valve. If the tank doesn't have at least 150 psi in it, a spring fully opens the valve, and your LP hose and 2nd stage receive whatever pressure is left in the tank. The 2nd stage works similarly, where it will deliver air until the pressure in the hose gets down to (almost) the ambient pressure in your mouth.

Oops, I certainly did got it backwards. The spring is on the other side of the piston or diaphragm. Thanks for correcting my misconception on how the regulator works. So we can actually breathe down to the ambient pressure.

This video shows how the 1st stage regulator works:

 

[billt4sf]

Before gearing up: Breathe air out of both regs, test the BC inflation and release, look at the SPG to verify a full tank.

Just before jumping in, breathe two - three breaths of the reg while looking at the SPG. If it moves at all, your air is not on all the way.

Especially important if you're doing a negative entry!

- Bill

 

[halocline]

Your description is correct as far as it goes, but it doesn't go far enough. Your 1st stage will continue to open until the IP reaches its 150psi set point. If it can't reach 150, it keeps trying, by simply going full open and staying there. Your 2nd stage works similarly. If it can't keep the downstream pressure it wants to, it simply opens all the way and stays there. So you can breathe your tank down until its internal pressure is equal to the ambient pressure at your 2nd stage.

I think you're close. Your description of the first stage is correct. The second stage is different, though, or I'm not understanding the way you have described it. The 2nd stage is a 'normal closed' valve which means with no pressure or under-pressurized, it's closed. It's set so that it will remain closed (barely) when supplied with IP. It opens mechanically when we lower the pressure in the case by sucking in air, which collapses the diaphragm, which pushes the lever, which mechanically opens the valve. When pressure equalizes in the case, the diaphragm returns to it's normal shape, allowing the spring to push the lever back to it's normal position which closes the valve.

But absolutely you can breathe a regulator down to ambient supply pressure. At that point it will be about as difficult to breathe as it is breathing on an un-pressurized reg without the dust cap on.

 

[Dan]

...But absolutely you can breathe a regulator down to ambient supply pressure. At that point it will be about as difficult to breathe as it is breathing on an un-pressurized reg without the dust cap on.

I hope I would never be in that situation at depth. If I do, hopefully my buddy would be nearby to assist. If not, I hope by ascending slowly from that point would reduce the ambient pressure enough to allow a bit of air to breathe in.

My rule of thumb is if SPG shows 750 psi (50 bar), it's time to ascend to the safety stop.

 

[dumpsterDiver]

It seems that there are so many misconceptions about how a tank/regulator will function as the tank is completely drained. I don't understand why people don't just experiment and before filling the tank, drain it down toward zero and hook the reg up and breath it down to nothing in the dive shop parking lot.

I think people will be surprised how long they can continue to slowly "milk" air from the tank.. Of course this is not something anyone should try while diving, but if they find themselves very low on a safety stop or something, it may give them the confidence to slowly sip their air and complete a safety stop - rather than shoot up.

 

[kafkaland]

It seems that there are so many misconceptions about how a tank/regulator will function as the tank is completely drained. I don't understand why people don't just experiment and before filling the tank, drain it down toward zero and hook the reg up and breath it down to nothing in the dive shop parking lot.

Because my dive shop would insist on a visual inspection before filling the tank again. Even when there was no chance whatsoever for water getting into the tank, like when breathing it down right in front of them.

 

[BRT]

Because my dive shop would insist on a visual inspection before filling the tank again. Even when there was no chance whatsoever for water getting into the tank, like when breathing it down right in front of them.

Might be time to get another dive shop. Or rent a tank from them and then see if it gets a new vis sticker when they fill it.

 

[ScubaWithTurk]

"Beginning" <> "OW Cert"

I am confused by what you are trying to say here. If you are telling me that the word beginning relates to the OW cert, then you are just saying exactly what I was saying. An OW certified diver is only certified to a depth of 60'. If you want to dive deeper you are technically supposed to be certified to that depth (i.e. -advanced OW or Deep)

 

[tursiops]

I am confused by what you are trying to say here. If you are telling me that the word beginning relates to the OW cert, then you are just saying exactly what I was saying. An OW certified diver is only certified to a depth of 60'. If you want to dive deeper you are technically supposed to be certified to that depth (i.e. -advanced OW or Deep)

Yes, you are confused. He said "beginning" is NOT equal to OW Cert. Think of your first dives as being a novice....hence the 60 ft limit. "An OW certified diver is only certified to a depth of 60'." is NOT a correct statement, no matter how many times you say it or how much you want it to be true.
'

 

[ScubaWithTurk]

Yes, you are confused. He said "beginning" is NOT equal to OW Cert. Think of your first dives as being a novice....hence the 60 ft limit. "An OW certified diver is only certified to a depth of 60'." is NOT a correct statement, no matter how many times you say it or how much you want it to be true.
'

I am not trying to argue here and I don't need to be right. What I need to do is have factual knowledge of the certified depth for OW. This is not about one person being right and another being wrong. This is strictly information sharing and exploration.

If, as you say, my statement is NOT correct, then why do I have to show an AOW cert to do a dive deeper than 60' ? Liability could be a reason however every songle piece of literature I can find all states 60' for OW.

Maybe I will start a new thread so this isn't hijacked anymore but I do believe that the disagreement here shows a major flaw in the systems put in place for training and certification.