Crossbar and isolator valve: do they help?

[LiteHedded]

HA! closing the isolator that's rich.
you gonna pretend to drown when my tank runs out, then when i'm dead open up your eyes and boogie out of the cave?

tbone you are too much

 

[2airishuman]

it's not about when you're curious about how much gas you have, it's about strategically keeping gas in reserve.

[....]

In a more modern sense, you could use that for strategic gas reserves if you had the ability to monitor your SPG and do something like this.
Isolate and breathe until you hit 2/3's of one tank. I.e. 800, 1000 or 1200psi depending on the fill
Open and turn the dive
Close and breathe until some arbitrary number. For me that would be about 500psi
Open and close

Assuming a normal cave dive and true equal penetrations it'd look like this
Start at 3600, turn at 1200.
1200 becomes 2400 at the turn with 2400psi in the bank on the left
Come out until 600psi, open and it becomes 1500psi
Exit cave with 900psi in one tank, 1500psi in the other
Open isolator and end up with 1200psi.

I suppose that would be one way to do it. I'm not a cave diver and probably never will be, but it seems to me, in your second example, you'd just equalize before looking at the SPG and turn at 2400 etc the way you usually do. I don't see any benefit in measuring the turn pressure based on the contents of only one side. Maybe I'm missing something.

In any event, when you had to air share, you would always have more gas in your tank than the guy breathing the primary which would give a better chance at getting out. If I'm diving in manifolded doubles and have a real OOA incident, the isolator gets closed as soon as the situation mostly resolves and we start moving. I don't want a panicked diver sucking down my gas to get out and causing a double fatality. *obviously in a cave that's resolved in sidemount or independent doubles and with more conservative gas planning in the real world, but I do isolate in a real or simulated OOA scenario for that reason

First I've heard of that. All I'm going to say is, you dive the way you want, and I'll dive the way I want.

 

[tbone1004]

@PfcAJ and @LiteHedded part of the reason I dive independent bottles, don't dive to thirds, and usually have at least one stage in the cave so things like that don't become a problem but if you have one with a much higher SAC rate on the way out with no other bottles in the cave, odds are it would be a double fatality. To each his own, but I don't want to be taken out in a body bag and I my dive buddies and I have agreed that there should really be no situation where we ever have to share air that is reasonable to plan for. I know this goes well against the GUE and DIR philosophies of buddy diving, but we plan everytihng as same ocean diving instead of buddy diving for a reason

This should be obvious, but this is no different than diving sidemount which I know the DIR community hasn't been able to adopt but it has always been talked about as keeping with the "default" gear and the requirements for always being able to donate what is in your mouth. Never about both divers have unrestricted access to the combined gas source. I have also yet to see or hear of any course that teaches extra conservatism in gas planning in a cave that is calculated out similar to rock bottom with elevated SAC rates or time to resolve problems. Only that thirds is the max limit and not to violate it and add to add conservatism, never how to calculate it

 

[2airishuman]

@PfcAJ and @LiteHedded there should really be no situation where we ever have to share air that is reasonable to plan for

Then why do you plan to close the isolator? Isn't that a plan?

 

[tbone1004]

Then why do you plan to close the isolator? Isn't that a plan?

reasonable to plan for means planning for more than 2 catastrophic failures. I plan to close the isolator because I value my life more than my buddies life and choose to mitigate a risk of a double fatality by giving an equal amount of gas to each diver. I choose not to dive doubles in a cave because I firmly believe that sidemount is a safer gear configuration which renders the opportunities where isolating a manifold becomes a real issue to be pretty negligible for me. In OW I'm almost always solo or same ocean diving, there is never any plan for a buddy to assist me in case of emergency, I don't believe in planning for it. It's a firm disagreement that I have with GUE and the team diving mentality. I believe a team is stronger than the sum of its individuals, but I don't believe you should be reliant on someone.
This is pretty small in normal recreational limits, but often times when at big depths, you just can't help someone or you become a statistic with them. I prefer to take that concept and apply it to all of my diving. If I can get my buddy out I will, or make his exit easier in any way I obviously will, but if the choice is him or us, then it's him

 

[PfcAJ]

reasonable to plan for means planning for more than 2 catastrophic failures. I plan to close the isolator because I value my life more than my buddies life and choose to mitigate a risk of a double fatality by giving an equal amount of gas to each diver. I choose not to dive doubles in a cave because I firmly believe that sidemount is a safer gear configuration which renders the opportunities where isolating a manifold becomes a real issue to be pretty negligible for me. In OW I'm almost always solo or same ocean diving, there is never any plan for a buddy to assist me in case of emergency, I don't believe in planning for it. It's a firm disagreement that I have with GUE and the team diving mentality. I believe a team is stronger than the sum of its individuals, but I don't believe you should be reliant on someone.
This is pretty small in normal recreational limits, but often times when at big depths, you just can't help someone or you become a statistic with them. I prefer to take that concept and apply it to all of my diving. If I can get my buddy out I will, or make his exit easier in any way I obviously will, but if the choice is him or us, then it's him

I don't think any one here is suggesting to "rely" on anyone.

 

[stuartv]

I don't think any one here is suggesting to "rely" on anyone.

I don't know about anyone else, but my training for accelerated deco dives is to plan one of two ways. Either, plan so that I can complete all my deco on back gas (in which case, my deco cylinder just lets me get out faster), OR, plan so that I don't need more than half of the deco gas I'm carrying. The latter is the generally preferred method. When planned that way, the training is that if I lose my deco gas (e.g. deco cylinder valve O-ring blows out), my buddy has the deco gas I need. And vice versa.

On a deco dive planned that way, I believe I am totally relying on my buddy (in the event I lose my deco gas).

Are you suggesting that everyone else here plans a different way than I was trained? Do you all always plan such that you can complete all deco on your back gas (or other gases you are carrying for yourself), if necessary?

If you plan your deco the same way I was trained, then isn't everything you say about this subject built on a foundation of relying on a buddy?

Tom's plan seems eminently pragmatic. But, I do wonder how well that plan would survive a direct strike from the real world.

"We're not out yet, but my isolator is closed and my buddy has just drained his side of my tanks dry. I have 700 psi left in my tank."

Will you fight your buddy off until he drowns in order to get out? Even if you think you could possibly get out and have 250 psi left in your own tank (but you can't really be certain)? If you haven't made the decision, in advance, that you WILL fight off your buddy until he drowns, then why bother closing the isolator in the first place? Will you have a mental milestone? "If he makes it to here, I will open the isolator again. But, if he doesn't make it this far, then I'm keeping it closed and letting him drown." How precisely will you calculate that milestone? Will you condemn your buddy based on a some quick mental arithmetic and time/distance/gas estimates? Or will you do a serious attempt at the utmost accuracy in establishing your buddy's deathline?

I don't know what I would do and I'm not saying Tom or anyone else is right or wrong. I think I would rely on my training, which includes proper gas planning to prevent either of us from dying - and (so far) does not include closing my isolator - and trust (hope!) that we planned well enough that we are both able to get out - or neither of us is getting out.

 

[Caveeagle]

Wow, this thread took an unexpected turn..

Agreed on the data point, I think public shaming has been a cause for the lack of data. If someone posts "I jumped off the back of a boat with my valves off" someone else will say "what an idiot you are"...

Yes, I think It would be good if we had more "near miss", "gear failure", or "SNAFU" reports. Anonymous would be better so we could avoid most of the drama.

But even then, it would really take a large sample of DATA to have a reliable conclusion about relative frequency and risk of each component. I.e.: Tank oring, burst disk, valve, etc.

FWIW: I have become comfortable with using an ISO-manifold. I check my valves at gear up, before desc, anytime I notice contact with tank/valve, and try to make a habit of checking when I hit turn psi. I noticed a LH valve that was ~1/2 closed once when breaking down gear post dive. I was not sure if I had started to close up and got distracted, or had a semi roll-off. In any case, checking often can't hurt.

..I think I know which 104's you got. There were 3 sets for sale and I was really tempted to buy all 3.. The stories those tanks could about the places they've been.. I don't require an isolator. Heck, I dove for years using a yoke manifold (I'm sure you did too!) and there sure as heck wasn't an isolator on them, but I think they're valuable.

Haha.. you nailed it! These are early versions and don't seem to be quite as heavy as a battleship anchor. ️. I must admit having similar thoughts about the "Dive Log" these would have if only... I am tempted to make at least one dive with them and all my "1991 vintage" swag! ..104s, Seatec wing, English light, Aladdin, and of course.. my jetstreams.

..probably get "stroke" of the week honors from the local cave popo

You can get just the isolator crossbar for the manifold if you choose to add one.

Yup, I suspect many sidemount divers are literally tripping over their discarded ISO valves.

 

[PfcAJ]

I don't know about anyone else, but my training for accelerated deco dives is to plan one of two ways. Either, plan so that I can complete all my deco on back gas (in which case, my deco cylinder just lets me get out faster), OR, plan so that I don't need more than half of the deco gas I'm carrying. The latter is the generally preferred method. When planned that way, the training is that if I lose my deco gas (e.g. deco cylinder valve O-ring blows out), my buddy has the deco gas I need. And vice versa.

On a deco dive planned that way, I believe I am totally relying on my buddy (in the event I lose my deco gas).

Are you suggesting that everyone else here plans a different way than I was trained? Do you all always plan such that you can complete all deco on your back gas (or other gases you are carrying for yourself), if necessary?

If you plan your deco the same way I was trained, then isn't everything you say about this subject built on a foundation of relying on a buddy?

Minimum gas (you're reserving that anyways, right?)is roughly the amount of gas as it takes to deco on backgas for a single deco-gas dive. For instance, on a 150' dive for 30mins with 21/35, you'd need roughly 55cuft of reserve to get you though the deco if you lost your 50% bottle, which also pans out to be the right around the min gas value you need for a 150' dive (~60cuft).

On a two deco gas dive you've got options. If you lose the 1st gas you can extend stops (again, dipping into that min-gas reserve) and extend the oxygen time. If you lose the oxygen you have reserve 50% that you didn't breath leftover and you can breath that and when its exhausted use your min-gas reserve.

A buddy *helps* as you can get out of the water faster, but is not required to overcome a lost deco gas situation.

YMMV if you don't use standard gases

PS: I'm sure you can come up with some wacky scenario where this doesn't work. But generally, for most dives, it holds up.

 

[stuartv]

PS: I'm sure you can come up with some wacky scenario where this doesn't work. But generally, for most dives, it holds up.

My scenario is currently only being trained to use 1 deco gas. I'm starting Trimix and will be trained for 2 gases pretty soon. But, at the moment, I dive according to my training and only use 1 deco gas. So, my dives are such that I could not complete my deco on back gas if I lost my deco gas. I am reliant on my buddy to give me the extra half of his deco gas if I lose mine.