possible? 2nd stage failing & supplying air above ambient?

another scuba science question: in modern american/european branded regulators, is this type of failure possible? & would the reg shoot out of your mouth before any damage was done? thx
b

ballastbelly,

There ya go, thinking again. Keep it up; I enjoy your questions.

The short answer to your question could be: “Yes, of course – it’s called a free-flow and you practiced it during class”

But even though you said "second stage failing", I think you’re talking beyond that. In class you simulated a free flow caused by a second stage issue which releases the intermediate pressure (typically around 135 psi above ambient) that always lurks in the hose between your first and second stages. I think you’re actually asking about a first stage failure in which cylinder pressure would be fed directly to the Intermediate hose, and thus to your second stage. Since I’m not sure about that answer, I’ll wait for the regulator experts to respond.

Good question.

knotical

ballastbelly:

would the reg shoot out of your mouth before any damage was done? thx

Click to expand...

Not if you clamped your jaw around the reg fast enough AND superman clenched your lips. Instead of the regulator shooting out of your mouth, you would simply explode.

But I think the reality is much more boring. An average person should be able to bite down hard enough to retain the regulator mouthpiece when a freeflow occurs, but your lips will not have the ability to retain the air flow. You will simply get a lot of bubbles spewing out of your mouth. Annoying, noisy, no need to panic. Likely the end of your dive.

P.S. I too love your questions. What IS the matter with your brain?

"Instead of the regulator shooting out of your mouth, you would simply explode."

Now let's not scare people, that hardly ever happens. It's been weeks since an OW diver exploded.

ummmm.... wouldn't it just go out the exhaust valve of the regulator????????

ummmm.... wouldn't it just go out the exhaust valve of the regulator????????


Yeah but that wasn't as funny as an exploding diver.

If Superman sealed your lips around the secondstage and stuck his fingers up the exhaust shroud to hold the flappers closed. Yes, you could explode.

I'm no expert, but having experienced a 1st stage free flow I might be able to indirectly answer that question. As your IP creeps (or shoots!) upward your second stage will also begin free flowing. One of the nice things about the 1st stage is that it acts as an inline restriction in addition to a pressure regulator. This restriction is great enough that you'll rarely be exposed to the full tank pressure. You'll be losing a lot of gas very quickly, however should have enough time to find your buddy, switch to a pony, or formulate another escape plan.

I believe this is also something that should be taught in your OW. Worst case scenario you can remove your rig, shut off the bottle and remove the 1st stage. By cracking the valve open you can bottle breath on your way up to the surface. After the time required to react and close the bottle it's quite possible you'll only have a few hundred PSI left.

In my situation I was with a buddy. We recognized the failure and switched to his alternate. By the time we got my tank shut off I had about 1000 PSI off of a new tank.

upstream reg.? anybody vintage wanna chime in?

ballastbelly:

another scuba science question: in modern american/european branded regulators, is this type of failure possible? & would the reg shoot out of your mouth before any damage was done? thx
b

Click to expand...

The second stage exhaust valve has a much higher maximum flow rate than the second stage inlet valve, which means that even if you mashed the purge button down, you would only be able to achieve slightly more than ambient pressure.

I've tried it a number of times in the pool and have never been able to get it to do anything more than puff out my cheeks a little.

Note: if you do this underwater with a flooded reg, make sure you cover the hole in the mouthpiece with your tongue, since it will blast some water down your throat with astonishing accuracy if you don't.

flots.

I had a 2nd stage free-flow a few weeks ago, and captured the regulator blowing out of my mouth on video. While it was happening, I didn't realize it had free-flowed. It had stopped before I recovered it. My recall was that I stared dumbly at the camera for 2-3 seconds before moving to recover, but the video showed that my reactions were faster than my time-sense.

Reading up later on free-flows, it seems that the flow force can vary greatly. During my OW training, I experienced two mild free-flows in the pool, with the excess air exiting through the normal exhalation exhaust. The instructor stopped them with taps on the purge button, then we surfaced and he adjusted the flow effort. I'm debating whether a computer or reg set will be my next purchase...

[video=youtube;xppBZOnZFi8]http://www.youtube.com/watch?v=xppBZOnZFi8[/video]