Pony Bottle Regulator Setup

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Can you please enlighten me as to how you work out MOD if you don't know the % oxygen in the gas mix?

He can't. He put his opinion in that you don't need to understand nitrox to dive it in a pony ( not the position of any agency I'm aware of ) and now only writes one line quips to challenge me as if I don't know what I'm talking about. Of course you need to know 1) how to analyze tank contents 2) select a max ppo2 (1.2, 1.4, 1.6 ) and why you are selecting it 3) calculate the mod for a mix and 4) calculate the best mix for a planned max depth. You probably should also know what VENTID is. I'll admit alot of the other dive planning like EAD and CNS clock isn't important since it's a pony but seriously... don't do trust me dives.

---------- Post added March 24th, 2013 at 06:51 AM ----------

That depends on your car's gas mileage, or in this case on your breathing efficiency, the length of your ascent and of your mandatory deco stop. I guess my question is a little rhetorical, or rather questioning if my 6 cu.ft. pony would do me any good in that scenario.

Gas planning is going to be part of any serious dive training such as solo diver, intro to tech, cavern, DIR-F et al and of course if you do some googling and ask your mentors some questions you can learn it on your own. That said, IMO, a really good yet simple answer is to find a luxfer 40cf pony tank. It slings really nice as an AAS and if your diving progresses into those other areas you can O2 clean it and use it for a deco bottle. IMO, anything other then that and you'll be selling it one day to buy another tank.
 
He can't. He put his opinion in that you don't need to understand nitrox to dive it in a pony ( not the position of any agency I'm aware of ) and now only writes one line quips to challenge me as if I don't know what I'm talking about. Of course you need to know 1) how to analyze tank contents 2) select a max ppo2 (1.2, 1.4, 1.6 ) and why you are selecting it 3) calculate the mod for a mix and 4) calculate the best mix for a planned max depth. You probably should also know what VENTID is. I'll admit alot of the other dive planning like EAD and CNS clock isn't important since it's a pony but seriously... don't do trust me dives.

---------- Post added March 24th, 2013 at 06:51 AM ----------



Gas planning is going to be part of any serious dive training such as solo diver, intro to tech, cavern, DIR-F et al and of course if you do some googling and ask your mentors some questions you can learn it on your own. That said, IMO, a really good yet simple answer is to find a luxfer 40cf pony tank. It slings really nice as an AAS and if your diving progresses into those other areas you can O2 clean it and use it for a deco bottle. IMO, anything other then that and you'll be selling it one day to buy another tank.

Agree with your analysis of requiring the % O2 of the contents to work out MOD. I wonder what oxygen exposure level he is prepared to attempt? “Trust me” dives might work in the short term "maybe" but sooner or later it will bite you. Murphy always lurks. I know divers do go to 70-80-90 metres on Air but many have had issues or not come back at all. Yes you can do it, but at what point does your unique body and metabolism quit on you and shut down, hence recommendations on 1.4/1.6 exposure rule.
 
That said, IMO, a really good yet simple answer is to find a luxfer 40cf pony tank. It slings really nice as an AAS and if your diving progresses into those other areas you can O2 clean it and use it for a deco bottle. IMO, anything other then that and you'll be selling it one day to buy another tank.

It looks like I'm going to have to replace my 6 cf "toy bottle" with a much bigger one. I purchased it years ago on the recommendation of the instructor that was certifying me for AOW, and luckily haven't had to use it once. Glad at least I didn't fall for the hype of the Spare Air, which also was more expensive then.
 
It looks like I'm going to have to replace my 6 cf "toy bottle" with a much bigger one. I purchased it years ago on the recommendation of the instructor that was certifying me for AOW, and luckily haven't had to use it once. Glad at least I didn't fall for the hype of the Spare Air, which also was more expensive then.

So you were previously doing planned deco dives below 100 feet using a 6 pony bottle and now you read something on the internet and figure you now need a 40 cu-ft tank? Did you do the math?
 
No, I haven't been doing any deco dives at 100ft, all of my dives have been buddy dives to no more than 65ft. The only time I've gone to 100ft was part of the mandatory AOW class with my instructor. There was a stage tank setup on the line by the dive boat at the time.

My earlier post about the emergency scenario was a worst case scenario, just that. I am also planning a half day, 2-tank no penetration dive trip to "wreck alley" in the San Diego area next month, with a potential max of a 100ft.
 
No, I haven't been doing any deco dives at 100ft, all of my dives have been buddy dives to no more than 65ft. The only time I've gone to 100ft was part of the mandatory AOW class with my instructor. There was a stage tank setup on the line by the dive boat at the time.

My earlier post about the emergency scenario was a worst case scenario, just that. I am also planning a half day, 2-tank no penetration dive trip to "wreck alley" in the San Diego area next month, with a potential max of a 100ft.
Well do the math, you sure as hell don't need a 40 cu-ft pony to do THAT dive! I personally allow my young son (14) to dive 90 feet with a 6 cu-ft bottle.
 
Again, the hypothetical was 100 to 110 ft, WITH a mandatory deco stop, and an OOA emergency, not the "perfect world" dive that one would plan and hope for. In your opinion, a 6 cf would suffice in that world, but a couple of posters above seem to favor a MINIMUM of 24 cf.
 
Again, the hypothetical was 100 to 110 ft, WITH a mandatory deco stop, and an OOA emergency, not the "perfect world" dive that one would plan and hope for. In your opinion, a 6 cf would suffice in that world, but a couple of posters above seem to favor a MINIMUM of 24 cf.

Do the math.. do the numbers and you tell me.....I would do the dive with a 6 no problem, but I would not plan on running out of air and going into deco. I avoid deco with a 6.. but let's see your numbers..
 
Again, the hypothetical was 100 to 110 ft, WITH a mandatory deco stop, and an OOA emergency, not the "perfect world" dive that one would plan and hope for. In your opinion, a 6 cf would suffice in that world, but a couple of posters above seem to favor a MINIMUM of 24 cf.

Capacity of a redundant air source is dictated by two factors:

1) The diver's air consumption rate.

2) The worst-case scenario time that the redundant air source would have to sustain the diver.

That worst case would be a loss of primary breathing gas at the end of the bottom phase of the dive: max depth, max nitrogen loading, max time to surface (ascent and deco obligation).

- A responsible diver would also factor in the capability to share air during that ascent, at least doubling the volume of redundant gas carried, from that previously.

- Air consumption would be prudently calculated at an accelerated consumption rate, in expectation of some incident-stress on that ascent.

For me, any deep, deco or overhead environment dive is planned according to (at least) rule-of-thirds. I wouldn't be using a pony for such dives - I would have full doubles redundancy. However, if I were to use a pony, the volume would represent at least 1/3rd of my main tank. The dive would be planned/undertaken on rule-of-thirds, so I'd have a 1/3rd contingency reserve in my primary tank and an 1/3rd redundant reserve in my pony.
 
It looks like I'm going to have to replace my 6 cf "toy bottle" with a much bigger one. I purchased it years ago on the recommendation of the instructor that was certifying me for AOW, and luckily haven't had to use it once. Glad at least I didn't fall for the hype of the Spare Air, which also was more expensive then.

To get the right cylinder for your application you first have to look at the diving you do, where you dive and what you may be exposed to. If you dive in a quarry that has a bottom of say 20 metres, or a reef with a maximum limited depth, you could happily use a 3 litre cylinder for emergency air. If you dive over banks in open ocean with the potential to be sucked down to 70 metres or doing blue water diving its another different story again. If you dive deco (well how long is the bottom time thus required deco time?) maybe an 11 litre sling cylinder is what you need in this case. This also depends on your back gas setup. Are you only ever going to dive single cylinder and only rec diving? Are you going to dive twin manifolded and if so what size cylinders? there are so many combinations to think about. No one setup will meet all this criteria.

What you need to do is to work out the type of diving you are doing, work out normal gas requirements and see if with normal setup you meet that. Then work out at the deepest possible depth (within reason), how much air you would need to get to the surface with any deco/safety stops (and plus some). Then you can work out the sling cylinder size you need.

As an example I use 2 x 12 litre manifolded cylinders with air, and one 5.7 litre sling cylinder with 50% Nx. This means in the back cylinders I have enough air to come from my deepest point in my dive (at the latest possible bottom time) to the surface with all deco and safety stops and still have spare. The sling cylinder is simply a deco gas I can use but not counted as emergency gas as I cant use it below about 18m. So in fact I can do the dive with no sling cylinder at all. If I want more bottom time then I need bigger back cylinders or another sling air cylinder.

Now if I were doing a NDL dive (recreational dive) to say 30 m, I would use a 3 litre sling cylinder and that would give me about enough to come to the surface and have some spare. If your air consumption is higher you may need a larger cylinder, if its lower then 3 litre cylinder may be fine. That's how you work it out rather than just guessing what you might need.

Now whether you get a 20 cu foot or 40 cu ft depends on a number of things like first "the maths of what you need", then personal choice, do you want to drag around a heavy cylinder you don't really need? Are you potentially going tech some time in the future in which a 40 cu ft might be a better long term buy. You need to think it through first before spending your hard earned money.

I know I have wasted money on getting what I think I might need only to find my thoughts were in the wrong direction. I guess we all do it and its frustrating but that's the learning curve. I wish I had gotten 300 BAR DIN from the word go. I now have 4 perfectly good K regs sitting in my dive box not needed. When I bought them I was guided by what is normally used in Australia for recreational diving. In hindsight I would recommend everyone go to 300BAR DIN straight away. If you never go tech it doesn't matter, DIN can be used for normal diving, but if you do you go tech you can use all of your DIN gear, and if its 300BAR DIN regs they fit both 235 BAR and 300BAR cylinder valves. I haven't been to anywhere in the world yet that doesn't have DIN or DIN/K tank valves, and anyway I have some adapters to use at a pinch.
Thats what I would do and the process to find what I should use and buy.
Look at;
Dive situation/style/area/location
Dive depth (and potential depth within reason)
Dive risks
NDL/Deco
Air consumption rate
Required bottom time
Potential future diving needs
Ease of use of the gear
And yes do some maths to prove your cylinder at least satisfies gas requirements. Hope that helps

---------- Post added March 25th, 2013 at 02:33 AM ----------

Again, the hypothetical was 100 to 110 ft, WITH a mandatory deco stop, and an OOA emergency, not the "perfect world" dive that one would plan and hope for. In your opinion, a 6 cf would suffice in that world, but a couple of posters above seem to favor a MINIMUM of 24 cf.

Well I am looking at the maths with your dive
6 cu ft=169 litres gas (sorry I am metric)
assume 110 foot=35m therefore average ½ depth to surface is about 17 m=2.7ATA
Assume 25 l/m gas usage
Rate of ascent=9m/min therefore ~4 min to reach the surface (give or take)
2.7*25*4=270 litres
Safety stop gas required at 5m for 3 min
1.5*25*3=112 litres
112+270=382 litres
Therefore unless I have something wrong here, without a deco you will need more than 6 cu ft you need about 14 cu ft.And I will stand corrected if my maths are incorrect.
 
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