Valve Drill Logistics

[ae3753]

All this talk of which thing to shut down first... why not shut down both at the same time? Once you have your teammates attention, you have two hands to manipulate valves with.

 

[limeyx]

All this talk of which thing to shut down first... why not shut down both at the same time? Once you have your teammates attention, you have two hands to manipulate valves with.

Well, what I do is

- reach up behind me w/right hand and feel for bubbles (way better than trying to listen in a cave). In o/w, listen, and also look. At the same time I signal my team and swim towards them with the light in left hand. Yes, this means I am biased toward "right-side" failures. This is unless I can obviously see bubbles from a "left" side.

I only have 2 hands

Once one post is shut down, then I can either
1) purge that post down which tells me some more information about what failure it is
2) isolate which tells me nothing about the failure and only saves me gas if I have a tank neck or burst disk failure (which I am assuming once I enter the water are less likely than reg failures). And we are back to the original point -- if the assumption that it is a reg is correct, you save more gas by not isolating. If it is not a reg you save more gas by isolating.

 

[grazie42]

well,

1) by always going to iso then right, you make everything the "unknown" case (you are guessing right instead of looking/feeling)
2) You only benefit in your case if a tank O-ring or burst disk goes. If you do not isolate first, you "gain" gas in all other situations (except where the isolator itself fails then we both lose as there is nothing you can do)

So essentially you are betting that a burst disk/tank valve/O-ring is more likely to fail than a 1st or second stage, and I am betting the other way. If a regulator goes (1st or 2nd) I have more than 1/2 gas left and more than in the isolate first case.

1) I ONLY close the isolator first in the "unknown case"...this is the "worst case" and hence why it is the one practiced in the valve-drill...If I know (or believe I know) it´s the right post I will (and have) closed that first.

In the unknown case I don´t always guess right, I choose the one I think is failing and I think that by taking the time to close the isolator I give myself some breathing space to gather more data and so make a more "educated guess" than if I´d been forced to go for one or the other as soon as I hear the bubbling...

2) To my mind you are approaching this in the wrong way...The object isn´t to save the most gas, it´s to save enough gas to make it out.

In the "unknown case", closing the isolator first always(except for isolator failiures) saves enough gas to exit, nothing else does because sooner or later you´ll guess wrong. Closing the isolator first is always beneficial, over time, because anything else just saves gas that serves no other purpose than acting as an extra weight on my back (literally) and will eventually lead to my losing gas that I need to exit...

 

[TSandM]

Closing the isolator first is always beneficial, over time, because anything else just saves gas that serves no other purpose than acting as an extra weight on my back (literally) and will eventually lead to my losing gas that I need to exit...

(italics mine)

I don't understand this statement. It appears to be saying that closing a post is saving unneeded gas. Personally, I would always like to save as much gas as possible . . . I dive sixths in a cave, and I don't object to hauling out two thirds of the gas I started with!

 

[Mike Edmonston]

(italics mine)

I don't understand this statement. It appears to be saying that closing a post is saving unneeded gas. Personally, I would always like to save as much gas as possible . . . I dive sixths in a cave, and I don't object to hauling out two thirds of the gas I started with!

Exactly, and not to mention that the anxiety and accelerated breathing rate caused by the freeflow will USE UP that extra gas rather quickly.

 

[limeyx]

Exactly, and not to mention that the anxiety and accelerated breathing rate caused by the freeflow will USE UP that extra gas rather quickly.

Right -- I think this is another crux of the matter.

Some people see 1/3's as "safe", and as long as you have 1/3 (1/2 of the 2/3 of gas you penetrated after isolation) you are safe to exit.

Some see 1/3's as an absolute minimum and would rather preserve more gas if possible because you really do not want to exit on another divers long hose which is going to slow things down.

I'd rather have a (to me) higher chance of saving more than 1/2 of the remaining gas, but I do appreciate that given

- the rarity of the event
- how long it really takes to shut things down

that we could be being overly picky here

 

[do it easy]

Are we really talking about thirds or turn pressure? Thirds will only work in some conditions, such as a spring, no current, ideal airsharing exit, etc. Turn pressure *should* account for the spit hitting the fan so that the not-too-ideal air sharing exit actually works. Exiting independantly is just free icing on the cake.

I thought that maybe I would go for the right post first, unless I was close to turn pressure.

And yes, we are being overly picky!!

 

[grazie42]

I haven´t dived for 2 months so I reserve the right to be picky

What I´m saying is that if I plan a dive on thirds, I had better be prepared to exit on 1/3, otherwise I need a new plan. If having only 1/3 or a valve-failiure is enough to cause increased breathing rate and anxiety, I have no business planning a dive on thirds (the idea is that 1/3 should be enough even if you have a buddy hanging on your longhose isn´t it?).

I feel that exiting on someone elses longhose is a symptom of a bad dive plan (barring catastrophic failiures) so while it´s certainly something that should be a "non-issue", it´s also something that would make me reconsider my planning or my proficency...

I´ve been sloppily using 1/3 in my examples because the math is easier and because it´s the absolute minimum I´d use for an OE-dive...

Also if we leave the "theoretical arguments" behind, closing the isolator first doesen´t mean that you loose the entirety of the "other" third, just as closing one post first and being wrong doesen´t automatically mean that you save less than 1/3 but then we´d be talking "real world" and be left with nothing much to argue about...

 

[Mike Edmonston]

If having only 1/3 or a valve-failiure is enough to cause increased breathing rate and anxiety, I have no business planning a dive on thirds

Remember that thirds is a minimum, although most divers use that as their turn pressure, in some scenarios (syphons,etc...) it is not sufficient.

(the idea is that 1/3 should be enough even if you have a buddy hanging on your longhose isn´t it?).

Assuming that your failure happens at max penetration, 1/3 will be enough to get one of you out, or both of you 1/2 way out. Who lives, and who dies... Rock Paper Scissors??

I feel that exiting on someone elses longhose is a symptom of a bad dive plan (barring catastrophic failiures) so while it´s certainly something that should be a "non-issue", it´s also something that would make me reconsider my planning or my proficency...

Not really sure if I follow you on this one. I agree that barring catastrophic failure, you should not have to exit on someone's long hose, but what if someone else has an issue and they have to exit on YOUR long hose? And yes, like you said we do plan (as best we can) for failures, but how is that a bad dive plan?

I´ve been sloppily using 1/3 in my examples because the math is easier and because it´s the absolute minimum I´d use for an OE-dive...

Agreed

Also if we leave the "theoretical arguments" behind, closing the isolator first doesen´t mean that you loose the entirety of the "other" third, just as closing one post first and being wrong doesen´t automatically mean that you save less than 1/3 but then we´d be talking "real world" and be left with nothing much to argue about...

When the **** hits the fan, we do the best we can! We use our best judgement and best guess to isolate either the post, or the isolator, hoping that we are right. All in all, as long as we "plug the leak", we should make it back to post another day.

 

[grazie42]

Assuming that your failure happens at max penetration, 1/3 will be enough to get one of you out, or both of you 1/2 way out. Who lives, and who dies... Rock Paper Scissors??

What I meant was that if you plan your dive on thirds, you´d better be able to get out on 1/3, even with a buddy hanging on your longhose (because (s)he´ll be using your other 1/3)...