Diving Nitrox with a pony bottle - theoretical

[scubadada]

I have air in my pony, good from any depth where I might be using it. I have enough gas to make a normal ascent and safety stop from that same depth.

 

[johndiver999]

I just bought a 20cf pony bottle (delivered to my Mom's place in Florida). It will be going straight to the LDS for assembly and fill. I'll never buy a whip for it.


A whip is somewhat expensive, but it is very useful - especially with a gauge. What if the pony free flows on the first dive? What if it leaks on the boat? what if it leaks a little over a two week period between dives - do you want to make another trip to the dive shop just for that? what if you use it for real on the first dive - then your dive day is over?. What if you want to practice with it?

If the pony gets completely empty, then getting a fill at the dive shop is often free, but it is so convenient to top it off at the start of the day - topping the pony off from 2,500 to around 3,000 from the main tank is hardly noticeable for a small pony.
If you have a 19 cu-ft bottle - then it may be important (for safety) that it be completely filled before a dive . A slow leak on a small pony will drop the pressure more than a similar one on a big tank. with a whip on board, you should never be tempted to dive with a pony that has leaked down and thus compromise your safety. Face it, if the bottle leaks down to 2,000 psi over night, are you not going to dive, or make the decision to just dive with it "low"?


Once you get a whip, you may also find it useful to transfill between main tanks before or between dives as well. It really gives you a lot of options. I know it sounds like a sales pitch, but I find myself using one a lot.

 

[James79]

If a whip seems expensive, think about this option
Tank Equalizer for $2.50
I use a variation of meathod A @couv details in that thread. As noted by others, it gives you options. Also, my usual buddy (13 y.o. son) doesn't use a pony, or as much air as I do... So I transfill the pony of his tank, we both end up with similar air available (measured in time, not volume), and the pony is full without recourse to the shop.
I feel more options are always better than less!
Respectfully
James

 

[W W Meixner]

Say a dive is within nitrox dive depths but your pony bottle isn't nitrox and just air ... say you had to go to the pony from your nitrox main tank, would you expect to experience narcosis rapidly? What is the effect?

(Of course, it's better to have the pony filled with nitrox to begin with, but this is just a hypothetical.)

R4L..

 

[IDNeon357]

Once you get a pony you'll understand. You don't take a pony to the dive shop for a fill. You plug it into whatever tank you're diving with a transfill whip, and therefore it gets whatever your main tank has. It doesn't have to be 02 cleaned in order to contain nitrox that's already mixed. 02 cleaning is really for doing partial pressure blending to make nitrox where you introduce 100% oxygen, then thin it out with air. In fact, I don't think pony bottles regularly get VIPped. You could probably even skip hydro if you wanted (I won't be doing that). Some dive shops who sell banked nitrox might insist on 02 cleaning, but that's just a money grab and has nothing to do with safety.

For the most part, my pony gets filled before the first dive of a trip. It only gets emptied if I need to get onto a plane, as you shouldn't actually be breathing from it unless you've screwed the pooch in a major way. However, I have used my pony to work on the bottom of my swimming pool since I only needed 5 minutes to screw in a new intake cover.

Since it's filled with whatever in your main tank, the specific contents require no extra consideration. Besides, even if it had 10% CO it's only for emergencies. I'd prefer 10% co to straight up drowning. At least you MIGHT live.

10% CO would kill you outright? (just wondering), 10% is 100,000 ppm.

50ppm is considered the hazardous limit, leading to headache/nausea?

Regardless I get what you mean, just asking for specificity

 

[IDNeon357]

I think the lesson I gathered from this thread is: use the pony for the tank you're using. So that means if you have mixed-gasses in different tanks for whatever reason, you'll need a pony for each of those tanks with their respective gasses.

 

[kelemvor]

10% CO would kill you outright? (just wondering), 10% is 100,000 ppm.

50ppm is considered the hazardous limit, leading to headache/nausea?

Regardless I get what you mean, just asking for specificity

Yeah, I pulled a bad number out of the air. My point was that even if the gas in your pony isn't ideal, it's better than drowning.

 

[James79]

I think the lesson I gathered from this thread is: use the pony for the tank you're using. So that means if you have mixed-gasses in different tanks for whatever reason, you'll need a pony for each of those tanks with their respective gasses.

I believe a better way to look at it is that tech divers will have different mixes in larger quantity than a "pony" and various bailout options. For recreational (no deco), if you are having to use the pony, you're ending the dive... So exact O2 percentage is immaterial. If you expect to be on the pony long enough for mix to really matter, it's more of a "stage" than a pony.
Just my take... Worth what you paid for it!
James

 

[IDNeon357]

I believe a better way to look at it is that tech divers will have different mixes in larger quantity than a "pony" and various bailout options. For recreational (no deco), if you are having to use the pony, you're ending the dive... So exact O2 percentage is immaterial. If you expect to be on the pony long enough for mix to really matter, it's more of a "stage" than a pony.
Just my take... Worth what you paid for it!
James

Gotcha, changing "pony" to "stage" for mental reference. I always considered it a "back-up" meaning the dive is aborted, didn't know there'd be different terminology for the name of such a tank.

 

[James79]

Gotcha, changing "pony" to "stage" for mental reference. I always considered it a "back-up" meaning the dive is aborted, didn't know there'd be different terminology for the name of such a tank.

More accurately, a stage is part of the plan and is expected to be used, where as a pony is an independent emergency air supply... Like airbags in a car, installed but not to be used unless things go wrong