Back mount pony bottle

[Nick_Radov]

So considering the more likely scenario, I'm thinking a back mounted 19cu pony with it's own 1st and 2nd stage. Maintain the octo I currently have because I wont always need a pony bottle. That will give the breathing air I need while using what's left in the main tank for wing and drysuit inflation. The assumption is that if I ever needed to use alternate air, the dive is over. Maybe hang the pony 2nd stage on a necklace.

If you're going to carry a back mounted pony tank, then you essentially have independent doubles. Just completely mismatched and lopsided. At that point, why not use two identical tanks connected with an isolation manifold? That will be simpler, easier to manage, and give you real gas supply redundancy. You also won't have to worry about getting separate fills for a pony or having a different gas mix. There are relatively small double tank rigs which are no heavier than a large single tank plus pony and carry at least as much gas.

 

[SlugLife]

How often are you people using a pony if you have to top it off after every dive?

As a personal rule, I bring my pony (or redundant air) on EVERY dive, no matter the depth or time. I take a few breaths before entering the water, and then later a few mid-dive, for skill-maintenance, and to ensure my regs are always easily accessible by feel alone.

Topping up is just a matter of using a transfill-whip, and is a minimal amount of air. I don't pay to have my pony tanks filled (much less VIP-tax).

 

[grf88]

There are relatively small double tank rigs which are no heavier than a large single tank plus pony and carry at least as much gas.

Double 50's come to mind so if I am doing 2 dives on a charter I will need two sets instead of 2 larger singles. Twice the cost of tanks, VIPS Hydros and fills. Would those be reason enough. Manifolded are only redundant until the isolator valve fails, unlikely but not impossible.

 

[NYCrecdiver]

I actually use my oral inflator on every dive to inflate just prior to splashing.

Never thought of that. Adding to my routine.

 

[NYCrecdiver]

If you are diving Nitrox, do you fill the pony bottle with Nitrox or air?

I like to dive 32% and plan to top off my pony after each dive after my two 120s got filled again. I figure, when I first hook up one 120 with the 19 pony and then hook up the two 120s together, among both of them they would have lost only a small amount of gas. So my pony will be filled with 32% also. I don't dive deeper than 130.

 

[inquis]

I don't dive deeper than 130.

Hopefully you meant no deeper than 110 ft since you like to dive 32%.

 

[NYCrecdiver]

Hopefully you meant no deeper than 110 ft since you like to dive 32%.

MOD of 32% is 132 ft at 1.6 partial pressure.

 

[DAJ]

While the pp02 for that depth would be 1.6 on 32%, it’s not generally utilized as 1.4 has become the NOAA, industry, and military standard. 1.6 is normally reserved as a limit during deco only and not the working phase of a dive. Granted, your dive your call but that change occurred in 2015.

 

[Angelo Farina]

I'm considering setting one up. The only time I used one was when we were using surface supplied air, and thankfully never needed it. So here's my though process.

Worse case is I suck a tank dry. Not sure how someone could get to that point without realizing they are low in air, but it's worse case. More likely case is that I find myself low on air. At this point there is still enough to inflate the wing and drysuit but maybe not enough to get to the surface safely.

If this is your concern, a pony can be a solution, but I think it is simply "too much" for a recreational dive.
What I use is much simpler: a tank with a good old reserve valve.
If you forget to watch your SPG and end up breathing hard, you pull the reserve rod and you get back 50 bars, plenty enough for ascending and doing your safety stop.
If you want maximum safety, you need a Technisub spring-loaded reserve valve: this avoids the risk of pulling the rod in advance by error.
With a reserve valve your equipment remains lightweight and streamlined, avoiding all the complexity added by a pony tank.
Please be aware that I own a pony tank, and the band for mounting it in the center of my twin tank.
But I never used it in place of the reserve. The few times I used it, it was just for having more air for long deco dives. A larger twin tank had been better, but I do not own it...

 

[Rob9876]

Topping up is just a matter of using a transfill-whip, and is a minimal amount of air. I don't pay to have my pony tanks filled (much less VIP-tax).

I have a dumb question about transfill-whips: Does, for instance, an AL80 with 500psi left at the end of the dive, have enough pressure to top off a 19cf pony that still has 2,000 or 2,500 psi left? Or does the pressure of the donor tank have to be greater than the pressure of the pony tank?