Back mount pony bottle

[Angelo Farina]

That is a bad idea. Reserve valves have been obsolete for decades. They are mechanically complex and cause more problems than they prevent. Such valves are barely even available anymore and have to be special ordered if you can get them at all.
I don't understand why some divers are trying to over complicate a simple issue. Usually, this stems from being unclear on the basics, and attempting to compensate for doing one thing wrong by doing a bunch of other things wrong as well.
If you need extra gas when real redundancy isn't needed, like for a very long shallow dive, then sling a stage tank filled with bottom mix and use that first before your back tank(s). If you can't monitor your own tank pressure, then you shouldn't be diving at all, and no amount of extra equipment can possibly compensate for being mentally unfit. If you have a mechanical failure, then your buddy has your redundant gas. And if you need a higher level of redundancy than your buddy can provide then buy a real set of doubles with a proper isolation manifold and learn how to manage failures.
But setting up a ridiculous little "pony" tank as a mismatched set of independent doubles is the worst of all possible options. It's like showing up for a race wearing different sized shoes that you scrounged out of a dumpster. Maybe I'm just vain but I wouldn't be caught dead carrying a pony.

I see you your point and I agree on the last part.
But a reserve double valve tank on a reasonably sized cylider (15 liters steel, in my case), still makes perfect sense to me.
First of all, this is my setup since 1985, so I am well used to it, and changing anything will need adaptation.
My preferred reserve valve is the Technisub one. Truly simple, never had a problem in almost 40 years, and very safe, as you cannot pull it by error, thanks to its spring-loaded mechanism.
People criticising reserve valves usually never used a Technisub one. Most deprecation comes from people who employed only the crap J-valves of the sixties and seventies. The Technisub reserve arrived later, and possibly never reached US. So please, do not criticise a system which you have never seen in action...
The tank has two posts and two valves, so I can use two fully independent regs. A first stage or O-ring failure is not a problem, I just close that valve and use the other reg.
15 liters at 200 bar provide a decent amount of air, so reserving 1/4 for the reserve mechanism still gives me enough "normal" air for planning the dive not accounting for the reserve.
Regarding the SPG; it failed me at least 4 or 5 times in the last 45 years, so it is not 100% fail safe. And there are situations in which you cannot materially look at it very often.
So, having the tank with double valves and the reserve, I really do not see any reason for switching it for a smaller tank, with a single valve and no reserve, this will reduce redundancy with no benefit.
I understand that finding such tanks nowadays can be difficult in some areas (not here, where they are still common).
But if one finds such a tank, I think it is way better than using a pony tank.
Regarding doubles: I have a nice Aralu twin tank, but the manifold does NOT separate the two tanks. Instead the Technisub reserve DOES separate the two tanks.
I think that this kind of valve is better than the "modern" manual separation manifold, but discussing this here would be slightly off topic.
And yes, for deep dives I always used my Aralu twin set. Although the air capacity is substantially the same as my 15-liters steel, the twin tank provides some slightly better redundancy.

 

[inquis]

Although you are roughly correct, in reality these calculation can be slightly wrong, because you are factoring the "total filled capacity" of each tank (80 cu.feet), whilst you should use the REAL capacity (12 liters).

A minor nit, an AL80 is 11 liters water volume (11.1 actually) rather than 12.

FWIW, an equivalent "imperial" approach would use the tank factors (rated cuft capacity per 100 psi} in the weighted average. I have these memorized for my normal tanks, much as metric folks memorize the water volume.

 

[Angelo Farina]

A minor nit, an AL80 is 11 liters water volume (11.1 actually) rather than 12.

FWIW, an equivalent "imperial" approach would use the tank factors (rated cuft capacity per 100 psi} in the weighted average. I have these memorized for my normal tanks, much as metric folks memorize the water volume.

Correct.
However here tanks are either 10, 12 or 15 liters.
Someone here calls (improperly) "80" our 12-liters tanks.
Which, being made of steel, are rated at 232 bars, so in reality they provide much more than 80 CuFt of gas (98?).
A 12 liter tank is considered a bit small here, most people, me included, prefer a 15 liters.
12 liters is good for my wife, who has a very low air consumption.
The good thing of a 15 liters tank filled at 232 bars (hopefully at 240) is that you can fill with it a small pony tank (2 liters or 3 liters, like my one) loosing just a few bars.
If the pony is empty , total capacity will be 18 liters, so the final pressure after transfilling will be 15/18 of 240 bars = 200 bars.
This is considered a safe initial pressure for initiating your dive.

 

[NYCrecdiver]

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?

If you want to top off your pony, you'd need to do that at the start of your next dive when you've got 1 or 2 primary cylinders filled (in case of a 2 dive boat trip}. You can hook up primary 1 with the pony, let the pressure equilaze. And after that hook up your 2 primaries so that they equilaze. You'll end up with a bit less gas in both primaries but a topped off pony.

 

[grantctobin]

After having an equipment incident

Gear build issue*?

 

[BlueTrin]

I'm not one to tell other people how to dive, but....

...exactly this.

I have several extra loaner pony bottles, including 6cu and 19cu, and am always a little surprised how rare it is for someone to take me up on the offer. I don't really understand why people are embarassed to carry one. Maybe some see it as a crutch or training wheels?

After having an equipment incident (loose regulator hose), I like having the insurance that should nearly anything go wrong with my primarily air supply, it'll only ever be a minor annoyance.

As a bonus, it even made me more confident with servicing my own regulators. Not that I think I'd make a mistake after getting some experience, but if I did, I'd have a completely redundant system with me.

I think a lot of people never used one before, so they just don’t want to dive a “new” config.

 

[mgbrookman]

Here's a pic of the Shark. One strap to deal with and the whole mess can be removed and moved to another tank. Quickdraw is definitely a cleaner install.

View attachment 763526

Here's a video.

Been using these for 10 years now, still a great setup. As long as you use rubber tubing to keep the band clamps from slipping.

 

[Ocddog]

Big fan of the shark mounts. Set it up once, & good to go whenever you want.

 

[34109411]

You will not get much love on this forum for pony bottles as most tend to believe that if you are concerned about such things you should be diving doubles which actually give you a properly redundant system. Marginal increase in weight but you don't have to have 3 tanks, only 2, don't have to worry about filling that 19cf bottle, and everything is working regularly so that is likely what you will see from everyone responding.

Edit: I will give the disclaimer that they are obviously used in the commercial/PSD world when diving with FFM's and make use of switch blocks and what not so the diver doesn't have to share air and remove the mask due to concerns with contaminated water and what not. This is outside the scope of recreational diving and while I think FFM's should also be outside of the scope of recreational diving people seem to like them. To me they are just a necessary evil when I have to talk to people either in-water or at the surface.

In my opinion double are good if you are getting into tech diving. I use to cave dive 20 years ago but not anymore And was using doubles. I am not physically in shape to carry double rig anyway. As a solo diver now I slung a 30 cf under my arm and this is perfect for what I do. There is no need to use double

I am a firm believer and user of a back mounted 19cf pony along with a 120HP Steel primary tank. Because of this I also don't dive a separate octo and instead have an Air 2 on my BC inflator so that I have both a redundant and share air option for my main 120cf HP. This gives me an inventory of approximately 140cf of available gas. My 19cf Pony is fully charged and good to go and is basically a no frill fully available buddy that is always there for me and doesn't ever drink any of my beer. I do dive primarily solo.....or at least end up that way if hunting or videoing. Also, my 19 pony is not factored into my primary dive and/or gas management plan. It is ONLY there as an emergency option in case if a catastrophic failure of my primary system.

The other thing that I do that is a bit unusual is that I have a dedicated SPG for my Pony so that I can monitor and confirm Pony gas pre-dive, during dive, and most importantly if needed for an emergency. Having the Pony SPG lets me know if in an emergency I have the capacity to complete a fully controlled ascent and safety stop.

This pic is of my Pony Tamer system but I have since changed to a Quick Draw Easy Mount because its more conducive for travel and for the double tank straps on my Zeagle Ranger BC.

I know that there is a lot of negative karma on this forum when it comes to back mounted Pony's and Air 2's......but it works really well for me and most importantly is what my personal mindset is ready and prepared for....

i really like that setup I am just wondering if will be off balance: I use a 30 cf that I slung under my arm, but for next summer I am considering a 19 cf cause less bulky, I will like to try it back mount. Very good idea to see your spg. Possible also to eliminate one hose using a air integrated computer but cost more.

 

[34109411]

I always sling a 40 with a button pressure gauge.
View attachment 763528

Nice