Pony bottle questions

[NAM001]

I think you are right

I think what BugHunter was referring to is the amount of pressure in the tank required to overcome ambient + IP.

For example, at 132 feet you are at 5 ATM (surface 1 ATM, plus 4 ATM for the water over your head). Your pressure gauge is reading the pressure within the tank, and calibrated to 1 ATM.

So if you add 4 ATM of water pressure (4 x 14.7) you have an additional 58.8 psi of ambient pressure for the 1st stage to overcome... 150 IP + 58.8 = 208.8 psi to take a "normal" breath... looks like he added another 150 to get 350?

Or my math is off

Anyway, I think what he was getting at is the actual pressure reading that you would need to see on your spg to still get that last "normal" breath before it started to breath hard, then stop delivering air all together (at depth).

Best wishes.

 

[Bigd2722]

I have a 13cf and a 30 cf. I hang the 13 cf on the side of my backplate. I do not give my pony to anyone (but I can share it, if I decide to do so dictated by the situation). I sling my 30cf but that is primarily for a return to exit if I am solo diving.

 

[Xaryo]

if you want a pony, get a 40ft³ and rig it as a stage.

Why 40 instead of 30 or 19? it is for re-sell value. a 40ft³ will be much more interesting than any other size of "small" cylinder. Also, it is small enough you won't feel it if staged properly.

 

[flots am]

Why 40 instead of 30 or 19? it is for re-sell value.

Why would anybody buy a tank with the intent of reselling it?

Buy a tank because it's the right tank for you. Not the right tank for someone else 20 years later.

A 19 you bring on every dive is much more useful than a 40 that sits in the garage.

flots.

 

[BugHunterNY]

I think you are right

I was using those numbers as ball park figures - but your math is correct and does illustrate what I was trying to say. There are many stories of deep divers getting Into trouble, and their tanks seemingly empty, but after ascending a bit, additional gas is accessible.




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[Dr. Lecter]

Why would anybody buy a tank with the intent of reselling it?

Buy a tank because it's the right tank for you. Not the right tank for someone else 20 years later.

A 19 you bring on every dive is much more useful than a 40 that sits in the garage.

flots.

By the same token, buy the right tank for your diving - not the tank you think you're more likely to bring because OMG the 40 is so much taller and heavier. If you're too lazy to bring a 30 or 40 when that's what your diving really needs as a redundancy cushion, you have bigger problems than pony selection.

Then again, my redundancy needs involve loading 3-4 tanks into the truck after my 70lb CCR and 35lb DPV...and of those 3-4 tanks two will be 80s. My ability to sympathize with those not wanting to lug around a single 30 or 40 is slightly limited. If I stop doing deep dives one day, it will probably be because I've decided all the work outweighs the fun...but you damn well better believe I'll stop diving that deep before I get lazy enough to say it, almost enough bailout is good enough/better than nothing!

 

[industrious95]

I have a 13 cf and have been using it for over 10 years. If I ever need to replace, I'll go with something a little larger, but for a controlled ascent from 120 feet with a 7 minute safety/deco stop, it's enough air for me.

That being said, I've never heard of someone complaining they had too much air leftover in their backup tank when returning to the surface following an incident.

 

[Bob DBF]

I was using those numbers as ball park figures - but your math is correct and does illustrate what I was trying to say. There are many stories of deep divers getting Into trouble, and their tanks seemingly empty, but after ascending a bit, additional gas is accessible.

Those stories were probably more from the day of unbalanced first stages, when diving deeper or having less tank pressure made it harder to breathe from the tank, so the tank would seem empty well before it was. Before the SPG and balanced regs, one could get a feel for tank pressure by the effort used to breathe.

Balanced regs can feed you virtually all the available air in the tank at any depth (208# in the example) so there is some air to be gained on the way to the surface, but not nearly the amount from the unbalanced, which could have double that pressure, or more, when you feel it starving you for air. Balanced regs breathe fine until they run out of air and immediately quit delivering, the unbalanced just breathes harder and harder until you can't suck any more out, it is up to you when you quit trying and head to the surface.

Also, back in the day, we were limited to 60'/min ascent and no safety stop so the surface was a lot closer than it is now. In your example on an 80 you have about 1 1/2 cuft of air available for your 4 min ascent (- safety stop), the unbalanced reg would be 6 cuft, or more, for a 2 min ascent by a diver that has no SPG or J-valve and uses this procedure regularly to end a dive.



Bob
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It pays to know your equipment.

I may be old, but I’m not dead yet.