Pony Bottle: Valve On or Off while diving

[rfwoodvt]

Been musing around the idea of backup/redundant air in the form of a pony bottle for a while now and I've been wondering a few things.

Let's first start with a couple of givens:

1. 13 ft^3 bottle
2. Mounted on the main tank or on a Zeagle Zipper attachment on the BC (I have a ranger LTD)
3. Stage Kit type rigging
   1. SPG
   2. DIN first stage
   3. Second stage with long hose and retainer band

For some reason one potential and routine problem that comes to mind is sudden free flow of the pony second stage, whether at the surface or just because it doesn't like the position, or losing air through an incipient leak through a loose fitting or the like.

My gut says that the pony tank valve should remain closed until needed. Of course this would mean having immediate and ready access to the valve which in turn means the tank should likely be mounted valve down.

Am I barking at the moon or is there some merit to this thought?

 

[Marie13]

Charged but off.

 

[Angelo Farina]

The few times I did carry a pony tank for the whole dive, it was attached in the mid of my ARALU twin tanks. So it was far in the back, its valve was hard to reach.
Hence I did open it at time of entering water.
Furthetmore I do not like the idea of having a regulator not pressurized underwater. It is quite easy to loose some air from a secondary reg. If its valve is closed, after loosing the gas trapped in the hose, water can easily flow in...

 

[rjack321]

You don't need to have a sudden freeflow, even a slight dribble at depth is enough to significantly deplete your 13cf. Charge up the reg but turn the bottle off until needed. Every dozen dives or so when the pressure isn't totally full anymore you can use up the gas and get it refilled by doing a practice dive ending with it.

 

[tbone1004]

First. Don't use pony bottles, proper planning prevents the need for pony bottles. If proper planning can't prevent the need for a pony bottle then you need a fully redundant setup in the form of doubles or sidemount, both of which take up less space than a pair of tanks and a pony.

If you're going to use a pony bottle, please at least use one that is useful for rock bottom.
For 100ft, that is NO LESS than (4ata*1cfm*3min+2ata*1cfm*3min+1.5ata*1cfm*5min)/.95=26.8cf. That is what it takes to get one diver to the surface in an emergency. First value is conflict resolution, second is ascent, third is safety stop, the /.95 is because only 95% of a tanks pressure is considered usable since you need at least 150psi remaining for the regulator to work. 13cf is nowhere near enough.

Second-if you're going to use one anyway, it should replace one of the second stages on your tank, not be in addition to. I would recommend you replace the second stage around your neck with it and that way if you have a real emergency you pass your primary and switch to the secondary which is then attached to the pony. Leave the bottle on at all times.

 

[rjack321]

The few times I did carry a pony botyle for the whole dive, it was attached in the mid of my ARALU twin tanks. So it was far in yhe back, its valve was hard to reach.
Hence Idid open it at time of entering water.
Furthetmore I do not like the idea of having a regulator not pressurized underwater. It is quite easy to loose some air from a secondary reg. If its valve is closed, after loosing the gas trapped in the hose, water can easily flow in...

Just a few burps of the 2nd stage will turn 13cf into 8cf or less.

If it burps and the regulator floods just get it serviced.

 

[macado]

1. The size of the pony bottle required is largely a factor of your depth and RMV. It's a topic that has been discussed ad nauseam here but I'd recommend a slightly larger bottle (AL30 or AL40) for a better gas reserves. I don't have anything against AL13s per se but my personal opinion is you would be better served with something larger. Having said all that, an AL13 is still better than no redundancy and many will vehemently argue that's plenty of gas for a typical NDL (no decompression limit) dive at recreational depths.

One other factor to consider is if you have any plans on doing any technical diving in the future then an AL40 is a better option as this can be converted to deco bottle. AL13/AL30 are ill-suited for that purpose.

2. I'm unfamiliar with the Zeagle attachment but I'd highly recommend standard stage rigging and clipped to front d-rings and slung rather than mounted behind your primary tank. It's an overall much more flexible way of doing things. It allows you to visually inspect the bottle / regulator for leaks as it's in front of you and allows for easy manipulate of the valve.

It also allows you to remove the pony bottle in the event of an entanglement, to hand up the boat crew before climbing a ladder, or even handing the bottle off to another distressed diver in an emergency. All of which you can't do if the bottle is mounted on your primary tank.

There have been accidents/deaths where people with pony bottles mounted on their primary tank and were unable to reach them to turn gas on or accidently started the dive unknowingly on their pony bottle and ran out of gas.

3. I'd recommend DIN regulator (although some will argue yoke is fine especially if you are traveling frequently). Since this is a pony bottle for emergencies a mini-SPG (button SPG) is sufficient. a 40" hose (which is standard on most stage / deco bottles) would be sufficient. Again, if you have any plans of technical diving in the future then I would configure your "pony regulator" like a standard deco/stage bottle regulator.

There is some debate if a bottle should be on/off. I'd recommend "off and charged" as a violent free-flow can easily deplete your emergency gas reserve if you're not paying attention. There is risk of flooding the regulator but I'd rather personally flood a regulator than find out all my emergency gas is gone when I need it. It's easy to periodically crack the valve on/off during a dive to keep the regulator pressurized.

TL;DR - AL40, standard stage rigging and slung, charged but off, 40" regulator hose.

 

[Edward3c]

I dive with mine on. If I were to need it I want gas on demand.

Side slung so I can see and reach the valve easily.

 

[doctormike]

Charged (never submerge an unpressurized second stage, water gets upstream) and off. It doesn't take much of a free flow to drain a small pony.

CCR Bailout needs to be on, IMHO, because you may be struggling with an altered mental state due to bad gas in the loop and you need to be able to get that breath of fresh gas instantly.

With OC, if you suddenly went OOG, you would know it right away and you certainly can hold your breath long enough to open a valve.

And it's not a bad idea to check that it's still charged every once in a while, especially if you notice an air leak. See point one above.

 

[Marie13]

For those pounding the redundancy drum, it’s not uncommon for single tank cold water recreational divers (I’ve seen it quite frequently on the Great Lakes) to carry a pony just in case. I used to do it myself on most dives 60ft and deeper when I dived single tank.