Testing a Spare Air

[happy-diver]

Hey don't go just bolt some lead to you plate

yeah thats right, listen to me as I make a lead post in a spare air thread

yep egress, good for downed helicopter training in swimming pools

 

[DandyDon]

I could not make a normal ascent from 130 feet at twice my average RMV with the 6 cf. At closer to my normal RMV I could. I use twice my average RMV for my emergency calculations.

No, I carry a 19cf pony. It's a pain, but like insurance: I'd rather carry it and not need it than not carry it and need it. I left it on the boat last night for a shallow dive in Cozumel, but failed to add lead, so had problems with floating to the surface at the end.

Once in Cozumel, I left it on the boat for a reef at the top of a wall, got pushed off the top and down, thinking it might have been a good idea to bring it on the dive after all. I swam out ok, but felt dumb.

Hi @JackD342

In what situations do you see using your 1.7 cf Spare Air?

I can't getting enough from one to offset the loss of fumbling to get to it.

To put this into perspective for folks who are unfamiliar with redundant gas and/or RMV calculations, here is a list of various size cylinders and the equivalent pressure in an AL80. Many should be able to relate to this

19 cf 736 psi
13 cf 504 psi
6 cf 233 psi
3 cf 116 psi
1.7 cf 66 psi

Great analogy.

 

[Johnoly]

..thought I would share the experience.

I also started with a Spare Air unit and exactly as you described, shallow dives, etc. I use a 6cuft handheld detachable pony now. I'm one thousand percent in favor of ANY independent air source that doesn't have a first name no matter what size. As you try different dives, you'll figure out any and all equipment upgrades that work for your type of diving, budget and needs. I still have my spare air.

 

[2airishuman]

So I decided to actually see what happens when breathing from a Spare Air. No one would mistake this for even a cheapo reg, it takes some effort to suck air out of it, but it works. First test was at 4 m depth, finning vigorously to get back to my entry point. The air lasted for a little over 4 min, which my buddy found surprising given the small size of the bottle. Second test was switching air sources at 22 m depth and performing a standard ascent at about 10 m/min. Easily made it to 3.5 m depth (took 2 min), and had enough air left for about 1 min safety stop. I could have done a CESA from there if needed.
So from my POV this thing does what I expected it to do. If I should have an equipment failure or an OOA at 20 m or less, I can make it to the surface unharmed. I agree that if I should be panicking it may not last as long, but with >1000 dives under my belt I don't see this as a very likely scenario. I can clip it to by BCD where it is out of the way but easily grabbed, and under most OOA scenarios at <20 m depth it will allow me to get back to the surface. I hope that this will not trigger a flame war, thought I would share the experience.

I do agree on a number of points:

1. That actually testing a any redundant air source during an actual dive is an important part of understanding what it can and cannot do;
2. That the received wisdom at ScubaBoard, due to multiple layers of conservativism, tends towards redundant air sources that are unnecessarily large;
3. That carrying redundant gas is better than not carrying redundant gas.

Now, while I do not "hate" on spare air, there are some Facts to Consider. To wit:

• For most people, 3cf is not enough to get you back to the surface, on a deep recreational dive, using ascent rates that are reasonable. 6cf is marginal, depending on how deep, how much current, what else has gone wrong, etc.
• Using a pony bottle (of whatever size) with a sure-enough 1st and 2nd stage has certain advantages over a spare air, over the course of many dives. Among these are: Ease of getting fills, ability to confirm that you're diving with a full cylinder, ease of getting hydro tests, ease of regulator service. When I dive with a pony cylinder, I test breathe it. Every dive. (How else would I know that it works?)
  
• If you get a flat tire on your divemobile, you can't inflate it with a spare air, because it doesn't have a BC fitting where you can attach a tire chuck.

I have mostly switched to twinsets for deeper solo dives and find that I don't use a pony as much as I expected.

 

[CWK]

I have 3cf, 6cf, 13cf and 20cf pony bottles. I tend not to use the 3cf.

I prefer to calculate capacity based on 150bar instead of 200 bar. Most of the time my pony is trans filled to just below 200bar. Pre-dive checks and post dive depressurisation of the system continually reduces the pressure. If you factor in continually dropping service pressure over a 7, 10, or 20 day trip, a 13 or 20 cu ft pony

 

[CWK]

Apologies, accidentally posted the above before completing the post.

....a 13 or 20 cu ft pony may be preferable to. A 3 or 6 cu ft pony as it reduces the frequency of having to top up the pont.

 

[vjongene]

Hi @vjongene

You didn't say which model you were diving, I assume the 3 cf, they also make a 6 cf and a 1.7 cf.

This topic has been discussed many times on SB, the calculations are easy. I could just make it directly to the surface from 60 feet with a normal ascent at twice my average RMV with the 3 cf. I wanted enough gas to cover all my diving within recreational limits, so chose a 19 cf pony. Choosing a redundant gas source is an example of the right tool for the job.

Sorry, I should have been more specific. It was a 3 cf model.

 

[markmud]

Sorry, I should have been more specific. It was a 3 cf model.

Hi vjongene,

Great thread! I am amazed that you actually tested a spare air (mini pony). Most keyboard Scuba Police Special Agents have never experimented with/or practiced with spare air or a "real" pony bottle.

As for increasing your RMV by an "emergency" ascent factor-- it is a good idea. Doubling your RMV is probably about right for people who don't freak-out when they see a mouse or rattlesnake in their garage. If you (not the OP) are the person who fears his own shadow and then hyperventilates at the mere thought of it, yeah, get the 19cf, or better yet the 40cf stage bottle. YMMV! .Dive and let dive... dealing with different styles of diving.

I did all three of my solo training dives on one 13cf pony bottle. And we did not transfill between dives. I just did not use that much gas for the three ascents. I have performed practice pony bottle ascents from as deep as 105'. It is now second nature. An ascent is just an ascent, whether on a pony or not.

To iterate, a pony ascent is no different than any other ascent--why in the hell would a skilled diver freak-out while doing a pony ascent? If you (not the OP) fear a pony ascent, you should transition away from diving and try biking (although I have seen some nasty bike-wrecks on the Little Miami Bike Trail).

One criticism for the OP: Don't use your spare air to swim underwater for your egress point. Surface immediately; next, surface swim to your egress point. The giant scuba tank in the sky is your friend.

Question: Do you see my 6cf pony and it's second stage in my avatar picture? My 6cf is my buddy-diver special--when my named buddy swims off and violates buddy diving protocols, I rely on my no-name buddy. My 6cf or 13cf has been on every dive for the last 150 dives or so, solo or not.
I am that .

Pony on bro,
markm
PS: this discussion is based on recreational dives of less than 100 fsw depth, in benign conditions, right? Not tech diving in somewhat treacherous conditions or geography. We are not talking Cape Flattery, right?

 

[caruso]

• For most people, 3cf is not enough to get you back to the surface, on a deep recreational dive, using ascent rates that are reasonable.

Where do you get that idea from? Don't know about you but you but I can swim the length of a 40' I ground pool and back on one breath. Add a half dozen breaths provided by a 3ff cylinder and that's another 40-50' easy.

 

[markmud]

Apologies, accidentally posted the above before completing the post.

....a 13 or 20 cu ft pony may be preferable to. A 3 or 6 cu ft pony as it reduces the frequency of having to top up the pont.

Hi CWK,

Yeah, I had that problem with my 6cf bottle. I fixed it by bringing my transfill whip with me. Now, my 6cf is always topped-off. It is painless.

Pony on bro!
markm