To shop owners or owners of spare air tanks

[Attreui]

Hey all, I recently got a spare air "pony" and I had a question for dive shop owners or anyone who has filled one. They fill off of a fully charged cylinder. I normally rent my tanks and own everything else. But if I rent a tank and use it to fill this, it will not be full anymore. Can the shop top it back off before I dive? Is this common? And is there normally a charge for something like this? Sorry if it's a silly question, I just wanted to know what to expect when I go next time.

Thanks,

 

[jboneng]

I can't say for certain, because I fill my own tanks and always have, and I don't know what policies shops on the other side of the pond follows. But I suspect that no one likes to fill tanks for free, no mater how small the tank is. But I would guess they would be happy to top your tanks for a small charge.

Anyways filling a 0.44l 200bar tank from a 12l 230 bar tank will only drop the pressure in your main tank down to 223 bar, which is almost insignificant.

 

[Neilwood]

I can't say for certain, because I fill my own tanks and always have, and I don't know what policies shops on the other side of the pond follows. But I suspect that no one likes to fill tanks for free, no mater how small the tank is. But I would guess they would be happy to top your tanks for a small charge.

Anyways filling a 0.44l 200bar tank from a 12l 230 bar tank will only drop the pressure in your main tank down to 223 bar, which is almost insignificant.

I know at least one of my LDS charge a minimum of £2.00 for small cylinders compared to £4/5 for normal cylinders

 

[DavidFL]

I carry a Spare Air when I'm travelling to dive by air; I just fill it from one of the rental tanks on the first dive at the destination trip. The drop in pressure/capacity is so small that I don't see the need to have it 'topped off'.

 

[Shugrnutz]

You can also get a fill whip adaptor for it.

 

[Buoy_A]

But I suspect that no one likes to fill tanks for free, no mater how small the tank is.

Here in Southern California there's a chain of sporting goods stores called Sport Chalet that will fill pony bottles for free. I believe their max size for free fills is 20CF. I'm sure they figure that they would like the foot traffic and goodwill that it brings (Pony bottles are generally associated w. safe diving practices and are typically only used in an emergency situation. So they don't expect to be filling these every time you bring in your normal tanks. So this policy, in theory, doesn't require much more labor and implicitly endorses safer diving). I think this is a pretty slick business practice and wouldn't be surprised if other scuba businesses didn't also subscribe to it.

 

[kelemvor]

Unless you actually use the thing, then it should be rare for you to have to fill it. Do it once, perhaps top it up occasionally. You'll never miss the 3cuft a spare air holds anyway.

 

[Damselfish]

Any sort of backup is not something you should be using every dive, you would fill it once and be done with it for hopefully quite awhile. So if you have one tank a little bit low should be no big deal. You will probably get some tanks a little low and a little high as a matter of course anyway.

If this is truly one of the little "spare airs" do read up on them if you haven't and understand the limitations. You'll find many people consider them more useful for getting out of a ditched helicopter (really the original use) than coming up from any sort of depth, as they simply don't hold that much air. Perhaps better than nothing, although some people would even argue that point and say it gives a false sense of security.

(There are actually a variety of things marketed by the industry and sold by dive shops that sound like a good idea at first, but really aren't. But as long as people buy them they will sell them, it is a business.)

 

[Rhone Man]

My dive shop always used to charge me full whack for my pony. Their rationale (which makes sense to me) is that they are selling a service, not a commodity. Air is free - I am paying for their labour and use of their machine, hooking it up, processing, unhooking etc.

Sadly, they didn't apply the same logic to my doubles, and charged me double rate for those.

 

[tursiops]

In my opinion, the 3 cuft Spare Air is a disaster waiting to happen. Note that only 90% of that is available, because some pressure has to still be in the bottle for your second stage to work. A diver who is not stressed is probably using 0.5 cuft/min at the surface, so three times as much at 66 ft (= 1.5 cuft/min). Double that again if someone is stressed (= 3 cuft/min), or three times that if someone is stressed and working hard (= 4.5 cuft/min). So, at 66 ft, stressed and working hard, you've got about 36 seconds of gas. That may be enough to get you to your buddy. If you wanted to go to the surface, at 60 ft/min, that would take 66 secs. At 100 ft/min (not a good idea!), it would take 40 seconds.

If you really need a pony bottle (not a bad idea), 13 cuft is your minimum, and 19 cuft is better. Then you can go to 100 ft, have a safety stop, etc.