Valve (not a) drill

[Kevrumbo]

Well, I keep trying to be a good lemming, but the analytical part of me is hard to turn off

That's always good --detail it down, deductively analyze it to your satisfaction, and put it back together resulting in a cogent action plan (just like a good SOAP note)

 

[Kevrumbo]

Well, if your long hose shreds and you shut off the right post first, you've actually just done the optimal thing to reduce your gas loss. Shutting down the isolator doesn't stop the loss out of the right tank in that situation.

Plus, I think the moral here is going to be adaptable. If there's a huge bang and a massive jacuzzi behind you and your bowels immediately cut loose, going for the isolator may be a better choice. As a rule, though, I don't think i agree with teaching the isolator first, always. Its most likely to be something solvable by shutting down the right or left post, and if you can reach your valves you should be able to feel the bubbles coming out of one side or the other (otherwise it isn't much of a leak) and can shut down the correct one, that minimizes the gas loss. Shutting down the isolator first in the common situation actually wastes gas while you're doing that shutdown.

To recap, if you know which is the offending post, shut it down. If that didn't solve it or you're mistaken, then isolate and signal your buddy to come take a look & troubleshoot. If you've got a massive jacuzzi behind you, proceed to shut down Right Post & breath Long Hose down and switch to Back-up. If that didn't solve it, isolate & signal buddy to take a look and be ready to follow his direction. . .

 

[cerich]

To recap, if you know which is the offending post, shut it down. If that didn't solve it or you're mistaken, then isolate and signal your buddy to come take a look & troubleshoot. If you've got a massive jacuzzi behind you, proceed to shut down Right Post & breath Long Hose down and switch to Back-up. If that didn't solve it, isolate & signal buddy to take a look and be ready to follow his direction. . .

What a waste of good gas....

 

[matt_unique]

Without reading all 6 pages, the only time I ever "needed" to do a valve shut down was with a frozen reg. I was doing a deco dive on the U853 and my primary 2nd stage froze open. I had just taken an unusually large breath and knew that had caused it. I shut down the right post for perhaps 30 seconds, turned it back on and was set for the remainder of the dive. On deck I had the 2nd stage adjusted and it has never frozen since.

Your list looks good to me, I was throwing in my 2 cents via frozen regulator.

--Matt

 

[Kevrumbo]

<snip>.
Your reply is exactly what I asked not to get, which boils down to "this is what I was taught and it's DIR so it must be right" You used "heuristically sound approach for problem solving Post & Manifold Failures/Malfunctions" which sounds impressive but doesn't address my points, it side steps it with boilerplate.

Which part in particular do you disagree with? Why?

Show me where I'm wrong, not just a party line.
Best,

Chris

You're not wrong Chris, you just have a different approach and action plan. . .

Here finally is the qualitative and somewhat quantitative Rationale behind GUE's and 5thd-x's method:

Probably the most common procedure taught by the technical diving agencies is that whenever you have a failure that causes you to start losing gas, you first shut down the isolator. The theory behind this is that you know you will at least have saved half your remaining gas. We do not advocate this approach.

If you go to the isolator first, you get no confirmation of what the problem is, which means you have to go to one of the posts anyway. So in every case you'll need to shut down at least 2 valves. If you go to the post first, in the most likely scenario (1st stage failure) you'll only have one valve to shut down. You solve the problem faster, get started on your exit faster, reduce the amount of bubbles blowing around your head faster (which may be bringing clouds of silt down on your head if you're in a wreck/cave).

Effectively we're using the odds of failure. The types of failures that would force you to need to isolate would be:
Burst disc failure
Tank neck o-ring
Manifold o-ring

The chance of a burst disc failure, tank neck o-ring failure or manifold o-ring failure are extremely small during a dive. The pressure in the tank is continually decreasing and ambient pressure is increased as compared to the start of the dive.

On the other hand, regulator 1st and 2nd stages have a number of o-rings and moving parts, which are constantly being used throughout the dive. Therefore by far the most likely failure will be a regulator failure (1st or 2nd stage) which can be solved by shutting down the post.

So if you can speed resolution in the most-likely case, why not do that?

In addition, you can usually identify the location of the failure. If the HP seat in the 1st stage fails, then the 2nd stage will begin freeflowing. So if your necklace reg begins freeflowing, you know you have a left post failure. Likewise, if your primary reg starts blowing gas uncontrollably, your right post has failed. If the failure is such that it is not delivering high pressures to the 2nd stage, and is instead just blowing gas straight out of the 1st stage, you can usually identify by sound which side this is coming from. Note that this even works with thick wetsuit hoods. Again, if you hear the gas blowing from the left side, it is likely a left post failure; gas blowing from the right side is likely a right post failure.

So the procedure we use is as follows:

Try to determine where the failure is.
If you can identify the side, shut that post down.
If you can't identify the side, then shut your right post down - this is the most likely failure (since it is the regulator being used most actively)
Breath the reg down (or hit purge button) to depressurize line
If bubbles stop, you solved the problem. Get your buddy to look at it to see if it's fixable. Fixable or not, you should probably exit
If bubbles don't stop, isolate. Get your buddy to take a look and see if they can identify the problem.
One final note - whenever you contact (or come close to contacting) the "ceiling" (roof of cave, roof of wreck, etc.) you should always do a run-through of all your valves. Reach back and check that each of the valves is turnable and on.

No Party Line --just a better heuristically, logically, and consistently sound approach. . .