Valve/manifold procedures "in the real world"

[Tortuga68]

Because it tells you nothing about the problem

Well, you can do SPG diagnosis after an isolation, right? But if you shut down the left post, no gauge diagnosis possible - although as MonkSeal and someone else (sorry I forget who you are) informed me in the other thread I referred to, the gauge will only drop if it's a major leak (from the left post, after isolating), which is a fair point

To explain, the way I was taught was 1. isolate 2. bubble/gauge check 3. shut down leaking post/swap (if right post) reg (post purge). I've since been informed that I should do it in reverse order. I'm trying to understand why that's better.

AFAIR the advice was "try to locate where bubbles are coming from (left side or right side) and shutdown that post, proceede with diagnose, evaluate if bubbles are still present, proceede with further actions if required".

IIRC, there was advice in both threads about shutting the right post down first (bubble check notwithstanding/inconclusive) as the right post is 'more likely' to fail; but I'm still trying to understand why you don't isolate as a first step regardless.

In short, I am so far failing to see the advantage of shutting a post down before isolating.

Help?

 

[TSandM]

As I understand it, the goal is to preserve as much gas as possible. Shutting the isolator does nothing to stop the leak (assuming it is a leak which can be stopped). Shutting the post may stop the leak, if it is not a tank neck o-ring or a manifold failure. Such failures are extremely rare. Failure of moving parts is felt to be far more likely than failure of static parts, and this certainly seems intuitively correct. Therefore, the most likely way to stop a leak is to shut the post on the offending side.

I can't really comment on how easily one can identify the side where a leak is coming from. With the air gun, it wasn't too difficult. In real diving, I've only had very small leaks, and they've been more challenging . . . but a very small leak gives you plenty of time to decide what to do about it, if anything.

 

[rainman_02]

If you're trying to imply that I'm a cyber-diver...I have more decompression dives logged than post on SB...as well as more cave dives for that matter.

Not my intent. Should have put a line break in-between the comments as the only thing that was directly attached to your quote was the synopsis of situations. I was referring to the type of people who simply say things like "well you need to rethink your diving if..." and think that will solve these types of problems.


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It actually resolves one of my issues, which is questioning whether a valve drill will always identify a problem. It's the re-opening of the manifold that I'd not be sure about, whereas reading between the lines here it seems like the "standard procedures" are subsets of the valve drill chosen on particular basis, which is great.

So, if I were seperated and had an unknown failure I would start with the right post, isolate it and breathe it down before swapping to backup reg.

If the bubbles continue, I'd close the manifold. If the bubbles continue, I'd reopen right post, test and breathe from it whilst shutting down the left post - if this still hasn't fixed it, I'd check the SPG and see whether the pressure was dropping. If it is, I know that I've got a left post issue.

If the SPG is static, left post should be good - but with the isolator closed and breathing off the right post, I'm at risk off being OOG whilst the left post is shut down, so that needs to be reopened, but I'd still leave the isolator closed (if shutting down the post hasn't fixed it, it must be a manifold, burst disk or similar?). I'd probably breathe off the right post as long as possible whilst still monitoring the SPG for changes. As long as it's not dropping, I'd leave it and only swap to the backup reg when required.

To the OP,

A valve drill will NEVER identify the problem. It is a DRILL. Its sole purpose is to get you manipulating your valves and understanding which regulator and inflator are attached to which post. That's why it is in Fundies; it is a fundamental skill for later classes.

As I was taught...if you wind up with the right shut down and isolated...you can continue if necessary on your left as it still has the SPG and you know how much gas you saved. If you wind up with the left shut down and isolated...you should be on a teammate's long hose as you don't know how much gas you have.

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I raised similar issues in another thread and got some good advice but had further questions; however since I'd already dragged that thread off topic, I didn't think it was the right place to continue the discussion - this one seems more apt

1. I still don't get why you don't isolate first (before post shut down). A catasprophic LP failure can drain a tank pretty quick. Why isn't gas loss prevention the first order?

2. Advice in this thread/GUE is to shut right post first, breath it down and switch regs. If your failure is actually on the less common left post, and is serious (ie major failure), couldn't that lead to no air on your secondary?

What am I missing?

TIA

Post first is about gas prevention first. It is based on the "most likely" scenarios. In those most likely (o-ring extrusion on 1st stage, blown LP hose, 2nd stage free-flow, etc), shutting down the post first will save the most gas as shutting the isolator first still allows the reg to continue dumping gas from that side.

The issues that cause the need to isolate are a sufficiently low probability compared to the other scenarios that in the long run you will save more gas by assuming it is not the most catastrophic failure.

 

[Tortuga68]

As I understand it, the goal is to preserve as much gas as possible

Agreed! Surely this leads to isolation as the first step though? If you close the wrong post, you're just losing gas (from the leaking post) that you could have otherwise saved through isolating first?

Shutting the isolator does nothing to stop the leak (assuming it is a leak which can be stopped). Shutting the post may stop the leak

True, but you may get gauge diagnosis via isolation, as I mentioned before. Alternatively - if the leak isn't large enough to indicate on the gauge - what have you lost? The premise seems to be based on probabilities and I don't like that. We all know that the thing least likely to happen is what will happen

Of course there may be a situation where your first stage has failed and you can swap one from your stage bottle, and save gas that way. I don't know, I can't see a reason to change the way I learnt yet, but I'm happy to keep reading! Thanks guys

 

[TSandM]

If you wind up with the left shut down and isolated...you should be on a teammate's long hose as you don't know how much gas you have.

Interesting. I was not taught this. I WAS taught that the diver with the left post closed should be sandwiched between the other two, as he is the most likely to go out of gas. But putting that diver on a teammate's long hose immediately is essentially operating as though the "injured" diver has lost ALL of his gas, which sort of defeats the purpose of closing valves and isolating. After all, if it is an isolated left post failure, he may well have the majority of his gas left, and ignoring that as a resource doesn't seem like a good plan to me.

 

[Tortuga68]

Post first is about gas prevention first. It is based on the "most likely" scenarios. In those most likely (o-ring extrusion on 1st stage, blown LP hose, 2nd stage free-flow, etc), shutting down the post first will save the most gas as shutting the isolator first still allows the reg to continue dumping gas from that side.

Okay, I now see that preserving tank gas that way could allow a primary reg switch from a pony or buddy, making the back gas useable again; I wasn't thinking that far ahead - thanks

 

[Tortuga68]

Interesting. I was not taught this. I WAS taught that the diver with the left post closed should be sandwiched between the other two, as he is the most likely to go out of gas. But putting that diver on a teammate's long hose immediately is essentially operating as though the "injured" diver has lost ALL of his gas, which sort of defeats the purpose of closing valves and isolating. After all, if it is an isolated left post failure, he may well have the majority of his gas left, and ignoring that as a resource doesn't seem like a good plan to me.

...but if their left post is off, then their SPG will be dead,so how would you know how much gas they have left?

 

[Rick Inman]

...but if their left post is off, then their SPG will be dead,so how would you know how much gas they have left?

Most would have a good idea (shut off left post and look at SPG. Same in both sides at that point). But not breathing it is the same as having zero. And why would I really need to know? Dive is over - might as well use what's left.

 

[Bismark]

We all know that the thing least likely to happen is what will happen

Actually, we don't know this and in fact assume that the the most likely thing to happen will be what most likely happens..........(is that a tautology?) If you were just making a joke then we can both chuckle, however if you really plan to base your troubleshooting on this then I would suggest that you have an issue.

 

[Bismark]

...but if their left post is off, then their SPG will be dead,so how would you know how much gas they have left?

You can also quickly turn your left post on and off while looking at your SPG and see how much gas you have. This will work even with a leaking first stage on the left post.