HP/LP Hose Failure?

[tbone1004]

@SlugMug important to remember that in the case of the LP hose failure, the air is not escaping the tank, it is escaping via the first stage that is trying to maintain a relative intermediate pressure. Even in an unbalanced design.

In terms of partially close the tank, you can feather the tank on and off, but you can't slow the flow down to anything manageable. The valve design is not a needle valve that can regulate flow. It is essentially on or off. Share gas with your buddy or dive a redundant system if the second stage isn't working well enough for a direct ascent.

 

[MaxTorque]

It's possible to breath directly from the cylinder itself. Possible, but not really recommended, but the seat and thread pitch of the cylinder valve are suitable for a basic control of air volume.. Try it next time before you screw your first stage on, very carefully, crack the valve, and you can control the air flowing out really quite well. Could you do that underwater, in a panic, in poor viz, in a current, whilst trying to maintain your buoyancy etc? er, that's a rather different question!

 

[SlugLife]

@SlugMug important to remember that in the case of the LP hose failure, the air is not escaping the tank, it is escaping via the first stage that is trying to maintain a relative intermediate pressure. Even in an unbalanced design.

In terms of partially close the tank, you can feather the tank on and off, but you can't slow the flow down to anything manageable. The valve design is not a needle valve that can regulate flow. It is essentially on or off. Share gas with your buddy or dive a redundant system if the second stage isn't working well enough for a direct ascent.

I didn't consider how the 1st-stage affects airflow. I'm a little more skeptical about the "feathering" comment. You absolutely can use a tank valve to only release a small amount of air, I've accidentally bumped tank-valves causing them to release slowly. What I don't know is how the quantity of air escaping from a feathered-valve compares to what comes out of the LP side of a first stage.

This is one of those areas, where I wouldn't bet cash (or my life) on which answer is more-correct, but would want to see a real-world test. If I had a scuba youtube channel, and multiple redundant air supplies, it would be fun to test some of these ideas.

It's possible to breath directly from the cylinder itself. Possible, but not really recommended, but the seat and thread pitch of the cylinder valve are suitable for a basic control of air volume.. Try it next time before you screw your first stage on, very carefully, crack the valve, and you can control the air flowing out really quite well. Could you do that underwater, in a panic, in poor viz, in a current, whilst trying to maintain your buoyancy etc? er, that's a rather different question!

This matches my thoughts as well. I've slightly cracked valves before, sometimes unintentionally. I don't know how much air (i.e. cu/minute) would you likely see from a slightly-cracked open valve, versus a cut LP-hose. It's possible feathering about 75psi equivalent of air manually is impractical.

Also agreed with other comments about panic, viz, etc. It seems one of the most likely scenarios, where you'd have one of these catastrophic failures would be bumping into a hard ceiling. meaning you instantly have 3 problems. The best option of course is to be able to switch to an alternate air-source, like a buddy or redundant source (which I should have one soon). Practice might actually make it viable to surface from 130ft with 1500 psi from a broken octo. However, to practice, you'd probably want a redundant air-supply, and you're putting in enough effort you might as well buy one.