Any reason not to get a AL30, compared with a AL19?

[Esprise Me]

I hope this isn't too far off-topic, but it pertains to the question of the appropriate pony bottle size. I've heard it argued that your pony bottle should contain not just enough gas for a 30 ft/min max ascent plus safety stop at a "stressed" SAC rate, but also one minute's worth of gas at the maximum depth for "problem solving." It makes a certain amount of sense to calculate that when deciding the minimum pressure to have in your primary tank before you begin your ascent. I suppose you could get entangled just as you were starting to come up. But pony bottles are more about dealing with catastrophic gas loss; without that, you still have your main tank reserve to deal with any other problems. It seems to me that by the time the pony reg is in your mouth, your problem is either already solved or probably not solvable in one minute. But I'm curious what others think. Assuming a normal SAC rate of .5 cf/min, a stressed rate of twice that, and a max depth of 100 feet, that extra problem-solving minute's worth of gas adds 4 cf to what you would otherwise need.

 

[Shasta_man]

If diving here in your stated location, I would choose the larger as the cold water adds a little effort. More than enough is a better problem to have.

And color is easy, just coordinate with the split fins

 

[SlugLife]

I hope this isn't too far off-topic, but it pertains to the question of the appropriate pony bottle size. I've heard it argued that your pony bottle should contain not just enough gas for a 30 ft/min max ascent plus safety stop at a "stressed" SAC rate, but also one minute's worth of gas at the maximum depth for "problem solving." ...

I've been researching this for the last couple days, and read a bunch of threads on the topic & even started a thread. This is not based on my personal experience, so take it with a pinch of salt-water.

• 6cu - Somewhat useless & a waste of money, except at shallow depths. At depth, it's barely better than nothing, and may prevent drowning on a rapid ascent.
• 13cu - at about 120ft is small drowning-risk, but medium decompression-risk.
• 19cu - at about 120ft is negligible drowning-risk, but small decompression-risk.
• 30cu & 40cu at about 120ft is negligible decompression-risk.

On the flip side is convivence:

• 13cu - The spare pony-tank you have on you, is better than the one you leave at home, or on the boat.
• 19cu - Probably ideal balance of weight, size, and risk-mitigation. It's also good for travel. Since this is just for super-rare emergencies, light decompression-sickness when diving near recreational-limit is probably tolerable.
• 30cu - Good, but might as well go 40cu
• 40cu - Best for multi-use, such as tech-diving, an extra/spare tank for short/shallow dives, resale-value, or even extending dives.
• 80cu - You could always side-mount 2x 80s, and just always make sure to leave enough air on both for an ascent. That said, I'd be tempted to leave the 2nd 80 cu on the boat, or at home.

I'm currently leaning towards 40 cu for multi-use. However, 19 cu is also very tempting, and probably what I'd roll with if I owned both a 40 cu and 19 cu.

 

[SaltyFrog]

I've been researching this for the last couple days, and read a bunch of threads on the topic & even started a thread. This is not based on my personal experience, so take it with a pinch of salt-water.

• 6cu - Somewhat useless & a waste of money, except at shallow depths. At depth, it's barely better than nothing, and may prevent drowning on a rapid ascent.
• 13cu - at about 120ft is small drowning-risk, but medium decompression-risk.
• 19cu - at about 120ft is negligible drowning-risk, but small decompression-risk.
• 30cu & 40cu at about 120ft is negligible decompression-risk.

On the flip side is convivence:

• 13cu - The spare pony-tank you have on you, is better than the one you leave at home, or on the boat.
• 19cu - Probably ideal balance of weight, size, and risk-mitigation. It's also good for travel. Since this is just for super-rare emergencies, light decompression-sickness when diving near recreational-limit is probably tolerable.
• 30cu - Good, but might as well go 40cu
• 40cu - Best for multi-use, such as tech-diving, an extra/spare tank for short/shallow dives, resale-value, or even extending dives.
• 80cu - You could always side-mount 2x 80s, and just always make sure to leave enough air on both for an ascent. That said, I'd be tempted to leave the 2nd 80 cu on the boat, or at home.

I'm currently leaning towards 40 cu for multi-use. However, 19 cu is also very tempting, and probably what I'd roll with if I owned both a 40 cu and 19 cu.

Thank you. Very good summary.

This is pretty much what I had arrived on after this long thread as well.

19 cuft + 40 cuft would pretty much satisfy all your possible needs.
And if not planning to travel, then likely no need for the 19 cuft.

 

[RayfromTX]

I like my 19 and my 40. I've used the 19 to dive in rivers and creeks side attached to a simple harness with no bc and a 2 lb weight. It rides in my car for tires and such. It can also be a small travel pony. Buy both

 

[MichaelMc]

For those with 19s, how many charge and test breath cycles does it take to lower your reserve significantly?

Rough calculations say:
men inspiratory reserve volume 3.3 liter is around 0.1 cu ft
0.5 liter tidal volume is around 0.02 cu ft
Three breaths and I drain my short hose reg.
So maybe two sharp partial test breaths, a small test one, and a drain uses one third to one half a cu. ft.

Not purging and removing the reg, taking small test breaths above and below water, and avoiding purges and it would stay full much longer on travel. I'm not sure how practical not accidentally purging the line is though with surface handling.

Air travel wise, 19s seem the practical limit.

 

[SlugLife]

I like my 19 and my 40. I've used the 19 to dive in rivers and creeks side attached to a simple harness with no bc and a 2 lb weight. It rides in my car for tires and such. It can also be a small travel pony. Buy both

Stop tempting me!

(P.S. I probably will buy both eventually.)

 

[hedonist222]

For those with 19s, how many charge and test breath cycles does it take to lower your reserve significantly?

Rough calculations say:
men inspiratory reserve volume 3.3 liter is around 0.1 cu ft
0.5 liter tidal volume is around 0.02 cu ft
Three breaths and I drain my short hose reg.
So maybe two sharp partial test breaths, a small test one, and a drain uses one third to one half a cu. ft.

Not purging and removing the reg, taking small test breaths above and below water, and avoiding purges and it would stay full much longer on travel. I'm not sure how practical not accidentally purging the line is though with surface handling.

Air travel wise, 19s seem the practical limit.

good question

I noticed my al 30 went to 170 bar in about fifteen dives

this is from turning on/off and a single test breath before each dive

 

[Gandalf-the-Diver]

So going solo and based on my SAC, I probably only ever going to need a AL19 for rec diving.

But looking at the sizing and weights, as listed on DGX site:

Aluminum 19
4.38 Diameter
17.3 Height
7.9 Weight

Aluminum 30
5.25 Diameter
19.5 Height
12.3 Weight

Pros:
AL30 is almost the same size
but gives me 50% more air.
Price is only $10 more BTW, not that this is a big factor.
AL30 can be used as a deco tank if I were to go tec, while AL19 can not.

Cons:
is 4.4 lbs heavier

I don't see any other benefits to go for AL19, unless for the extra 4.4 lbs, which I'm fine with.

Am I missing anything?

I looked at the same size specs as you and opted for a 30cu. I moved up from a 13cu. I went with the30 and if you look at size, a 40 is actually considerably bigger than a 19, and a 30. But a 30 still remains neg buoyant when empty, not so much a 40.

 

[Satrekker]

I sling an AL19. I typically only carry it when I'm diving 30m+. One day I'll add an AL40, but it's probably just because I think it would be another useful tool in my toolkit. Would I use it much? I'm not sure, but it gives me an excuse to buy some more gear. ;-)