H-Valve or side mounted pony for wreck penetration

[dolphin64]

Hello All,

I am contemplating taking a wreck penetration course. The course instructor is advising either an H-valve or a side mounted pony bottle (side mounted to the single tank) of 13 or 19 cu ft.
I know little about H-valves but my concern comes from still working with a relatively small volume of air. I know that o-ring or burst disk failure at depth is unlikely as the pressure is decreasing in my tank with descent (thank you Mr. Boyle). I am wondering though about the risk of tank valve failure.
In terms of a side-mounted pony, I am concerned about trim. Any experience out there? As well, I am thinking volume.... and thought a 40cuft luxfer would be better but I am told that is too big.
I am very comfortable in the water and others often joke that I come back with more air than I left with (not true I assure you... but my SAC rate is low). Still the risk of entanglement or entrapment is real in a wreck and under that kind of stress, my consumption rate would undoubtedly increase dramatically.
I guess my instincts are telling me that to give myself the ultimate level of safety I need to be in doubles and very comfortable with the gear. Is that an overcautious attitude???

dolphin64

 

[rmannix]

I'd go with the pony.
the H valve provides redundancy for a reg failure but no backup air supply.
Trim issues are imperceptible with my 30 CF pony. For wreck diving I wouldn't get anything smaller than a 30.

 

[The Chairman]

Welcome to the Department of Redundancy Department. While here, we aim to answer all of your questions by answering all of your questions. In order to ask a question we merely request that you just ask the question.

In any wreck penetration, true redundancy is needed. This is best done with doubles and an isolation manifold. After that, the H-Valve is my choice and then a sling bottle or a combination of the two. A pony bottle, 19cf and less, does not give you a lot of maneuvering gas.

 

[Jason B]

I know that o-ring or burst disk failure at depth is unlikely as the pressure is decreasing in my tank with descent (thank you Mr. Boyle).

The pressure in the tank is decreasing because you are breathing the gas, thus reducing the volume which in turn is reducing the pressure. Boyle's law has no effect on a sealed container.

I agree that a 19cu ft is probably not enough gas for doing penetration dives nor is a single tank. You should be using the rule of thirds when diving an overhead.
I'd say get some doubles with an isolation manifold.

An Al40 properly slung is almost unnoticeable underwater.

 

[divingbuddy]

This is best done with doubles and an isolation manifold.

Agreed. You should definitely be comfort with doubles and the true redundancy they offer.

After that, the H-Valve is my choice and then a sling bottle or a combination of the two. A pony bottle, 19cf and less, does not give you a lot of maneuvering gas.

Avoid the potential entanglement issues by relying on a pony bottle. An H-valve will not provide redundancy in the case of a tank-valve leak. Manifolded doubles with an isolator should be a minimum if seriously entering an overhead environment such as a wreck. Just my two cents. Cheers!

 

[Jay Roy]

I would advise doing this course in doubles....and also, alot of instructors demand advanced nitrox and decompression procdures certification even tho the course specifications dont ask for it...

 

[jtivat]

While I agree doubles are the best, if you are not ready for that then I would go with and H valve and a slung 40. I have done many penetrations with this set up. One thing I like about a slung bottle as opposed to a back mount is the ability to move it or even take it off if needed in those tight squeezes or when it catches on something.

JT

 

[Diesel298]

While I agree doubles are the best, if you are not ready for that then I would go with and H valve and a slung 40. I have done many penetrations with this set up. One thing I like about a slung bottle as opposed to a back mount is the ability to move it or even take it off if needed in those tight squeezes or when it catches on something.

JT

agreed
and a al 40 is like its not even there.

 

[drbill]

Pony. The H-valve offers no redundancy in the event that your tank valve's debris tube gets clogged. It happens (and did to me).

 

[T-Dog]

The 40 ft3 stage/pony bottle is probably a better long term option. You have the added gas and redundancy a already mentioned, but down the road if you upgrade to doubles the 40ft3 tank can be converted to a deco bottle.

Also with practice, you won't know an AL40 is even on your body. However, whatever gear config. you choose try diving it in a shallow controlled setting (pool, lake, quarry) before the class.

Also talk to your instructor and dicuss your options. He/she can help you out based on your dive background, the dive site for the class, and your long-term goals. Hey, that's what you're payin' for!

Finally, be careful about strapping extra cylinders to your gear - it's a slippery slope! A stage bottle here, a deco bottle there, and the next thing you know you're in the engine hold of some unknamed wreck looking for artifacts to discover the ships origin!

Good Luck, and Safe Diving!