Probably, but I imagine it would mess up your gas plan pretty good. How fast would it be, exactly, and how would you plan for the contingency?
Are single tanks used for wreck penetration? (+)
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Probably, but I imagine it would mess up your gas plan pretty good. How fast would it be, exactly, and how would you plan for the contingency?
nyresq
Contributor
...leaving the o-ring off one of the tanks for a quick test.
This I have seen and unless you tighten down the valves with a wrench, you will get a pronounced hiss when you try to fill it. Even tightened down with a wrench (which you should never do) you will still get a slow leak that will show a tiny bubble stream underwater or in a fill bath and will dump about 100-200psi per hour, so over night your tank will almost be empty. The threads are too restrictive to dump a tank in 10 seconds or a minute unless the valve was loose to begin with in which case when it gets filled, it will fail right away. Showing the urban ledgend of a catastrophic failure of a tank O ring "blow out" is a very slim possibility.
again I ask, does anyone have first hand experience with an o ring failure or have seen it first hand on a buddy?
This I have seen and unless you tighten down the valves with a wrench, you will get a pronounced hiss when you try to fill it. Even tightened down with a wrench (which you should never do) you will still get a slow leak that will show a tiny bubble stream underwater or in a fill bath and will dump about 100-200psi per hour, so over night your tank will almost be empty. The threads are too restrictive to dump a tank in 10 seconds or a minute unless the valve was loose to begin with in which case when it gets filled, it will fail right away. Showing the urban ledgend of a catastrophic failure of a tank O ring "blow out" is a very slim possibility.
again I ask, does anyone have first hand experience with an o ring failure or have seen it first hand on a buddy?
RichLockyer
Guest
Nope.
When I tested my SPG and breathability of my Apeks regs by taking the tank to zero (tank was headed in for viz the next morning), the valve turned when I handled the tank. It wasn't even hand-tight, and held air just fine for a year.
BTW: I can draw a vacuum on the tank with the Apeks reg... removed from the tank I can actually draw air through the system, and stop the flow by installing the reg's DIN cap.
Not enough to breathe, but some flow.
Dude, this is not an urban legend, it does happen. I work in a shop, and one of our rental tanks (AL 80, but I really dont think it matters what TYPE of tank it was) extruded the neck oring. This was not in the water, but after a weekend of dives, and the tank getting filled and then put in the rack. A little bit later, it starts leaking. No, its not a HUGE blowout, yes, you do lose gas rather quickly. I would not want to be inside of a wreck and have that happen to me.
For wreck PENETRATION, it should be with doubles. OR use the PADI rule for penetration, which is 130ft maximum distance to the surface, with redundant air supply (pony bottle) if I remember correctly (correct me if i am wrong)...
RichLockyer
Guest
Unless the material has been changed in the last 2 years, PADI's standard for wreck is the same as cavern... 130 to surface with a buddy. My instructor DID teach thirds, but I don't recall if it was in the printed material or the video. He also introduced us to the concept of the long hose, and showed me how horrible the "normal" hose was for the buddy while I was on my Airsource.
For the "real" dives in the class, I added a conventional "octo".
JimC
Contributor
Ignoreing all the issues with pony bottles. Your typical pony is completely inadiquate for penetration.
Assume your on a 130 with an K-Vavle and a 19cf pony. Lets say you use/plan 40cf for accent/decent/deco, inc reserve. You have 90cf left for your penetration. Cut that into 3rds' and your sitting at 30cf of pen gas.
Flash forward to a dive going perfectly well. Untill the everything goes to crapola at point of furthest pen. 30 in... 19 to get out. Not good news! Hope the pony wasn't taking place of a solid buddy, plan or you find a faster way out!
In this case you would need about 50cf in your pony to make it even have enough gas to be a bailout.
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I think most agencies are moving to 200feet to surface, 130feet max depth for cavern. I think GUE is the only agency that requires doubles for basic/intro penetration training.
Cavern can be done with a K-Valve. Intro to cave requires an H or Y valve, and special permision to use doubles. I'm not sure what the wreck courses require.
Even though I agree generally with your thinking JimC, the diver would have either runout of penetration (PADI standards) or even then, he'd probably get out with enough gas because of the rule of thirds, plus ascent gas PLUS pony anyways.
NOT that I agree with single penetration to begin with.....
It's been done, but I don't do it any more
NOT that I agree with single penetration to begin with.....
It's been done, but I don't do it any more
JimC makes a good point about 19 cu ft being inadequate. To be truly redundant in a overhead situation, your pony should be 1/3rd the size of your primary air supply to give it a fighting chance of being adequate to get you back to the surface in a worst case scenario where you need the whole 1/3rd to get out. Even then you are right of the edge.
30 cu ft would be adequate for an a 80 cu ft tank at 39% of it's air capacity, but falls short for 98's on up.
A 40 cu ft pony would be adequate for a 98, 104 or 120 but at that point you are almost better off weight wise with a set of reasonably sized doubles.
The other alternative is to limit your depth and penetration to the size of your pony. For example if you have a 19 cu ft pony you never go farther than the 19 cu ft of air required to get you home. You need careful and very conservative planning to make it work and would be limited to very short penetrations. Even then you would be right on the edge and could not afford for anything to go wrong. On a dive of any depth, you would realistically be limited to a touch dive only.
A buddy is a good idea, but I never put myself in a position of relying on one for a redundant gas supply. The potential of mechanical failure of any kind pales in comparison to the potential for a buddy to depart at an inopportune time with the needed gas.
30 cu ft would be adequate for an a 80 cu ft tank at 39% of it's air capacity, but falls short for 98's on up.
A 40 cu ft pony would be adequate for a 98, 104 or 120 but at that point you are almost better off weight wise with a set of reasonably sized doubles.
The other alternative is to limit your depth and penetration to the size of your pony. For example if you have a 19 cu ft pony you never go farther than the 19 cu ft of air required to get you home. You need careful and very conservative planning to make it work and would be limited to very short penetrations. Even then you would be right on the edge and could not afford for anything to go wrong. On a dive of any depth, you would realistically be limited to a touch dive only.
A buddy is a good idea, but I never put myself in a position of relying on one for a redundant gas supply. The potential of mechanical failure of any kind pales in comparison to the potential for a buddy to depart at an inopportune time with the needed gas.
OP
deepdiverbc
Contributor
Thank you for all of the advice, it helped me decide on the wing I want. When choosing a wing design for singles diving I won't add wreck penetration to it's list of tasks.
matt_unique
Guest
I just read through the threads and there are a few topics going on. Here's my opinion:
1.) Tank o-rings fail but it is of course extremely rare. I had it happen to me - pony bottle in fact. Fortunately it was sitting in my closet when it happened. It was fully charged to 3000psi and the o-ring squeezed out in one section and hissed loudly. The air loss was significant but it would have taken several minutes.
2.) Doubles vs. large single....well in my opinion more air and redundancy is always better. I never dive without a pony bottle because I like the idea of having a backup. For some wrecks you would most certainly prefer a single to reduce your overall size and entanglement potential negotiating tight quarters. Add an H or Y valve to your single tank as well as another reg (1st and 2nd stage) and you just added more redundancy to your dive system. Add a pony bottle and now you have three redundant regulators. I use my pony only as emergency gas. You need to know your SAC rates (air consumption rates) to properly calculate how much air you need for a given dive profile. Plan your dive such that if your primary system fails at the most critical time your pony will be able to get you back to the surface safely. The most critical time being the back of the wreck or the moment you are about to ascend from a deco dive or such.
3.) Size of pony depends on a lot of things. Shore vs boat dive and depth/time you are diving. I use a 13 CF pony for shore dives and a 30 CF pony for boat dives. The shore depths/time do not require the added risk and effort to carry a heavier 30CF pony system. Likewise the 13 CF pony does not provide sufficient air supply for a deep boat dive. Deep is a relative thing of course.
--Matt
1.) Tank o-rings fail but it is of course extremely rare. I had it happen to me - pony bottle in fact. Fortunately it was sitting in my closet when it happened. It was fully charged to 3000psi and the o-ring squeezed out in one section and hissed loudly. The air loss was significant but it would have taken several minutes.
2.) Doubles vs. large single....well in my opinion more air and redundancy is always better. I never dive without a pony bottle because I like the idea of having a backup. For some wrecks you would most certainly prefer a single to reduce your overall size and entanglement potential negotiating tight quarters. Add an H or Y valve to your single tank as well as another reg (1st and 2nd stage) and you just added more redundancy to your dive system. Add a pony bottle and now you have three redundant regulators. I use my pony only as emergency gas. You need to know your SAC rates (air consumption rates) to properly calculate how much air you need for a given dive profile. Plan your dive such that if your primary system fails at the most critical time your pony will be able to get you back to the surface safely. The most critical time being the back of the wreck or the moment you are about to ascend from a deco dive or such.
3.) Size of pony depends on a lot of things. Shore vs boat dive and depth/time you are diving. I use a 13 CF pony for shore dives and a 30 CF pony for boat dives. The shore depths/time do not require the added risk and effort to carry a heavier 30CF pony system. Likewise the 13 CF pony does not provide sufficient air supply for a deep boat dive. Deep is a relative thing of course.
--Matt
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