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Leave the Spare Air. Take the cannoli.
Boston Breakwater
"Outlaw." Solo Diver
Hello. With out a doubt....this is the best answer, in my opinion to the OP.You are asking good questions, so kudos to you.
The good news - equipment failures at depth are quite uncommon. That does NOT mean they cannot occur. But, if equipment is properly maintained, and good pre-dive procedures (including inspecting the O-ring on a yoke valve cylinder, or on a DIN regulator first stage) are followed, the chances of a catastrophic gas supply failure are very small indeed. Nonetheless, IF they occur, you may not have much time to reach your buddy to get assistance, or reach the surface if that assistance is not readily available. A good article providing actual hard data on the rate of gas loss associated with different equipment failures is available online ((Life Ending Seconds ADVANCED DIVER MAGAZINE By Curt Bowen)
As you probably note from the majority of responses in this thread, a Spare Air is not considered to be an adequate 'redundant' gas supply. It is relatively expensive considering what you get, and not particularly functional - 3cf of gas, at depth, is so minimal as to be trivial. Even the newer, larger Spare Air, with 6 cf of gas offers very little. Better than nothing? Yes. Anywhere near adequate as a redundant gas supply when a gas supply emergency occurs at 110 ft? Not at all. When I am diving a drysuit, I carry a 6 cf pony bottle as the gas supply strictly for inflating my drysuit. It really isn't a lot of gas.
Carrying a pony bottle of reasonable size (19 cf or larger) is a valid approach to providing a redundant gas supply. Preferences on size, and configuration differ. A 19 cf bottle is small enough to be attached to your primary 'backgas' cylinder, and some people prefer that. I do not like that approach, but that reflects my personal preference as much as anything. I prefer to 'sling' my pony bottle - attached by bolt snaps to a chest strap D-ring and to a waist strap D-ring - because I have better access to the valve, and regulator when it is in front of me. I use 30 or 40 cf bottles, and do not find either to be at all cumbersome or inconvenient, either on the boat, or underwater. The 30 is slightly smaller, and over the years I have gravitated to that size as a (very) slight preference for recreational diving redundancy. For the kind of diving you mention (70-90 feet), either size would work well. I encourage you to make the investment in such a bottle, and a regulator, and the rigging, and learn to use it. After a few dives, you won't know it is there.And, you should practice with it, to become 'fluid' in switching to the pony bottle regulator. I started learning to carry and use a 40 cf bottle years ago, on a trip to the Florida Keys. (And, yes, I caught some grief from other people on the boat, including the captain) when I carried a 40 cf pony on a 25 ft reef dive.
Several posters have specifically mentioned O-ring failures, and that concern merits comment. I have seen a few O-ring failures on cylinder yoke valves, at depth. Usually, they are manifested as aggressive bubbling and do not represent catastrophic failures. They are inconvenient, because the dive usually needs to be called. One alternative, to avoid that possibility, is to switch to DIN cylinder valves and regulators. In the western hemisphere, that is not the norm. But, I have used DIN equipment since I began diving some time ago - my first regulator was DIN - and have never regretted my choice.
I also second scubadada's recommendation to do a search here on SB. There have been a number of discussions on this issue, including some that were somewhat 'animated', and they are worth reading as well.
Thanks for speaking up. I like you, carried my slung bottles in some "Odd." circumstances/dive sites. (If, you will.)
I wanted to become proficient, and familiar with them before I ventured into deeper water.
Cheers.View media item 209700View media item 209702
The bent one was a Mexican fisherman. The other one was a tourist, but we were diving with an op owned by a Mexican fisherman. My guess is there were no dip tubes. Both of them went feet up just before their air stopped. Believe me, there are well know dive ops in Mexico that have equipment I don't want to dive with. Usually I do use their tanks. In January I sat on a log and watched regulators being serviced by a dive op that services a BIG resort. Unbelievably bad! Disassemble, toss in some parts, hook them to a tank, test breath and on to the next one.
This happened to me, too. The dip tube was there, and when thereafter I removed the valve from the cylinder (which was property of my diving club) I did find a lot of rust.
The air supply was not cut entirely in my case, and when coming back to normal head up position for ascending even more air arrived, as the rust did fall to the bottom of the cylinder.
After this bad experience I decided to buy my own tank, a 10+10 liters aluminium twin (Technisub Aralu).
PADI added this skill to the OW course back around 2013. At the beginning of the course they are allowed to look at their SPG to see how much air they have. Midway through the course they are expected to switch to approximating how much they think they should have, report that to the instructor, and then look at their SPG to confirm. It's a simple skill, and I found most students caught on to it pretty quickly. Helps to train students to recognize when something's not right with their air supply.
You know... that is a good point about the perils of using a Spare Air that I rarely see addressed in the pros and cons of these debates. Unless its secured to the diver somehow, there is a non-zero chance of dropping the thing before it gets in the diver's mouth.
woodcarver
Contributor
I always like it when folks who obviously have never even handled, let alone used, a device, want to denigrate and advise against it.
Depending on how one slings it, the SA is as simple to deploy as a bungied 2nd on a slung pony. It is also clipped off with a coiled leash that will prevent it being lost even if you dropped it. The bag that holds it has a pair of velcroed straps to retain the tank; identical to the one I use with my 13cu H2Odyssey pony. With the swiveling 2nd on the H2Odyssey reg, it is very similar to use as the SA; no hose.
The only valid objection I've ever seen with the SA system is volume. With the 6cu tank they've come out with, the volume has been doubled. Still a small tank. But it travels better than almost any other option. It's convenient to carry. So it will be more likely to be used on every dive. So, it really boils down to the question, is some air better than no air, at any depth. (Stuff doesn't always break at the deepest point in a dive). And a system that is so simple and unobtrusive that someone will carry it consistently seems to be a good thing.
Btw, I am trying to buy a SA 6cu tank. Already have the reg obviously. It will be perfect to set up on my GF's kit.
You might check the neck threads... 18x1.5 is a common one for that size, which is also the size used on a lot of paintball tanks. 3000 psi aluminum. Might be a cheap way to get a larger tank on the SA.
Respectfully,
James
MichaelMc
Working toward Cenotes
Every picture of one I have seen has not had a leash. I now see the accessory demo picture on their site for the $20 coiled 4' safety leash, usable for cameras as well. I also now see some amazon kits with the safety leash on the outside of the pouch, which would go up to the neck of the spare air.
ETA: The kit on LeisurePro has a leash.
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