purposes of manifold

[WarmWaterDiver]

Hmmm - barring an extreme entanglement, I think I could doff my BC to switch regulators on posts if necessary, with back mounted independant doubles. But, I'd rather do the Rule of Thirds thing to start with. The interim period during the switch would make me a bit uncomfortable, even while breathing my teammate's gas. This would also be true if they were side mounted.

But that's more of a cave forum thing. Looks like my cue to exit this thread. Have fun!

 

[scubafool]

The rule of thirds should be used in best case situations only. If anything is less than optimal, backing out the % of gas used to penetrate is a wise decision.

At any rate, switching regulators is, to my way of thinking, a last ditch effort type of thing, whether backmount or sidemount. Backmount, it seems to me, adds another layer of complexity in an absolute worst case situation. A good buddy who is right there is the best choice.

 

[Jason B]

A good buddy who is right there is the best choice.

I hear ya there!

 

[H2Andy]

oh yeah... give me a good buddy anyday

btw, i've had the pleasure to dive with Scubafool MANY times, and he's
an awesome buddy

 

[wedivebc]

Well, if all you are interested in are the benefits of an isolation manifold, my take on it would be as follows.

An isolation manifold allows you to attach two tanks together and breathe the gas that they both contain from either of two regulators. These regulators are attached to two different posts, either of which you can shut off at any time.This allows you to shut off the gas supply to a regulator if it malfunctions, while allowing you to breathe all of the gas that both tanks contain from the other regulator. Independent doubles, worn on the back, do not offer this.

Ah yes but, breathing tanks down as DA Aquamaster suggested would insure you would never have less than the required amount of gas in each tank to ensure you make it back safely. That means all these extreme measures such as swapping regs is totally unnessasary 1/3rd in 1/3 out 1/3rd reserve. No single failure can result in less than the needed gas.

 

[scubafool]

Yup, I agree, sort of. But in the event of a really BAD problem, it very well might take more gas to exit than it takes to enter. That is why I believe that 1/3rds is a best case rule ONLY. In a high outflow cave, that required considerable exertion to penetrate, and will require little effort to exit, 1/3rds very well might be a safe parameter. In a low/no outflow cave, with an unknown buddy, with other possible issues, 1/3rds doesn't make sense to me, whether from independents or manifolded doubles. Plan for the worst, and hope it never happens.

 

[scubafool]

And to try and get this thread back on track, I think that there is another plus to isolation manifolds compared to a straight bar manifold.

If there is ANY doubt as to where a bad leak is occuring, to ensure that you have enough gas to exit, all that is neccesary is to close the isolator. Even if you take an hour to get the offending post shut down, the other tank should contain ~ the same amount of gas as you used coming in, just in case your good buddy decided that he/she wanted your truck/van/car/helicopter/private jet/girlfriend.

 

[PaulChristenson]

Hmmm - barring an extreme entanglement, I think I could doff my BC to switch regulators on posts if necessary, with back mounted independant doubles. But, I'd rather do the Rule of Thirds thing to start with. The interim period during the switch would make me a bit uncomfortable, even while breathing my teammate's gas. This would also be true if they were side mounted.

But that's more of a cave forum thing. Looks like my cue to exit this thread. Have fun!

Did anyone say side mounts???

http://www.advanceddivermagazine.com/Armadillomanual.pdf

 

[DA Aquamaster]

Yup, I agree, sort of. But in the event of a really BAD problem, it very well might take more gas to exit than it takes to enter. That is why I believe that 1/3rds is a best case rule ONLY. In a high outflow cave, that required considerable exertion to penetrate, and will require little effort to exit, 1/3rds very well might be a safe parameter. In a low/no outflow cave, with an unknown buddy, with other possible issues, 1/3rds doesn't make sense to me, whether from independents or manifolded doubles. Plan for the worst, and hope it never happens.

Like manifolded doubles, you still have the option of increasing the reserve with independent doubles by adjusting the pressures at which you make the two reg switches in order to leave you with a larger reserve.

 

[Soggy]

I'm not sure that the isolation manifold is a necessary piece of equipment, since, to the best of my knowledge, no one has ever died as a result of catestrophic gas loss due to a burst disk or tank oring failure. You might be better off with a crossbar, since it doesn't have an extra valve as a failure point. Cave Excursions East has them in stock.

:1poke: