pony bottle-open or closed?

I sometimes use a 19cf pony while diving. Mine has a conventional yoke valve. After checking the reg. I leave the valve open and ready should I need it. I was just told that the "correct" way to dive with a pony is to keep the valve closed, as in rare situations the reg. could loosen and separate from the pony bottle. I'd appreciate some feedback on this.

I leave mine open, if I need it the last thing I want to do is have to stop and open it first. Have you ever had a reg come loose under pressure?

A more compelling reason to leave it shut is is to ensure that it doesn't free flow and drain the bottle without you noticing, leaving you with no gas when you need it.

rongoodman:

A more compelling reason to leave it shut is is to ensure that it doesn't free flow and drain the bottle without you noticing, leaving you with no gas when you need it.

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If it's slung, you would notice a free flow. I wear mine slung and keep it closed, but i can see an argument for both.

I'm glad you asked this question. I dived with a slung pony bottle with two different ops/instructors this summer and they each did it a different way (open, charge, then shut down for dive vs. open and leave open for dive). When I asked, they each had good reasons why they did it their way and seemed fairly certain.

I can see that there may be no absolute, but I'm going to be interested to read people's thoughts on the subject, to help me formulate my own opinion for future dives.

Here's how I would do it:

Slung = closed.
Back-mounted = open.

I would always sling mine, so there's your answer.

Depends on how easily you can manipulate the valve, monitor for leaks, and check the pressure. It is a trade-off between potentially loosing too much gas through leaks and freeflow (thus not having it when you need it) and rapid access to breathe from it.

If you can easily open and close the valve in the water, I would pressurize the regulator on deck and close the valve before entering the water. Entry is the most common time for a spare second stage to freeflow. Then pressurize just below the surface and check for leaks.

A DIN regulator is a good choice for a pony because it is more compact and has a little less entanglement potential. A first stage mounted pressure gauge or small SPG eliminates needing to remove the regulator to check the pressure before each dive.

Although a slung pony is nice for valve access and leak inspection, it is more hassle to gear up and less hydrodynamic than back mounted. IMHO, the most important consideration is that the pony is easy to use or there will be a tendency to not bother with it. It is reasonable to make the “carry/leave onboard” decision for any additional safety device based on dive profiles you feel justifies it. When you prefer not carrying that device, it will be left on deck for profiles that fall in the gray area — when you might need it but it isn’t worth the trouble.

Closed but charged, so you know the second is working (not leaking or freeflowing) and you have a ready breath of air at a time when you may be a little freaked out.

Well, think about when you would want to use a pony bottle. If you are out of gas, or someone else is out of gas, are you going to remember to turn the valve on? And if it's charged, the person taking the reg will get a breath or two and then be "out of gas" again . . . probably not great for someone who is already stressed.

The argument is made that, if the pony is back-mounted, you cannot see leaks -- which is true, but you can't see leaks out of your primary tank, either, and we all live with that.

I would mount the second stage where a freeflow from it will be apparent, and leave the valve open. And do a bubble check before the dive

With a pony bottle I will do like with a deco stage. It is what I learned and also to be consistent in the different dive like with a pony or a deco stage. So all the way closed and pressurized after a bubble check at the surface or about 3m to 6m. For most part of the dive, you won't need it, if it's not all the dive as it is your reserve, so what is the point to have it open and risk to don't be able to use it when needed. If it's back-mounted and difficult to reach the valve like Devon mentionned, I would do valve open, but it is not the way a wear my stages. I didn't know that practice. Anyway, be consistent is a key point for me.

You shouldn't be out of gas so quickly. In my view you can anticipate it by checking your consumption underwater based on your dive plan, like a free flow on your back can be seen by your buddy and you should check your gauge regularly, so the pony can assist you to reach the surface, it is just a safety bottle. Relying on your budy for gas sharing is not the way I dive, it is in second or third rank in the solutions.