Why do we put oxygen in aluminum cylinders?

[LiteHedded]

Well, let's use LP50s as an example, filled to 40 cubic feet. The buoyancy difference is one pound, with the steel being less buoyant:

LP50: 25" long, 5.5" diameter, 19 pounds empty, -2.4 buoyancy full, -1.7 buoyancy if filled to 40 cubic feet. source

Luxfer AL40: 25" long, 5.2" diameter, 15 pounds empty, -0.7 buoyancy full. source

That doesn't seem like a big deal. My AL19 pony is more negative than that and it isn't hard to clip off.



Well, again, using an LP50 as the example, 4 pounds makes a difference?

huh? yea 4 pounds makes a difference

 

[PfcAJ]

A 50 is bigger around, heavier on land, and more negative in the water.

Yeah, sounds great. Sign me up for that.

 

[LiteHedded]

A 50 is bigger around, heavier on land, and more negative in the water.

Yeah, sounds great. Sign me up for that.

they also cost a lot more

 

[The Chairman]

Hmm. Gear solution to a skills problem? Perhaps...

I never considered gravity to be a "skills problem".

I have two sets of bottles for my SF2. The pair that came with it are 2 L steel tanks and I use them in salt water where I drag a 40cf bailout. When I cave dive, I change them out for two AL19s so I can carry two LP95s as my bail outs (or two LP45s if I'm not going far).

 

[Wookie]

I never considered gravity to be a "skills problem".

I have two sets of bottles for my SF2. The pair that came with it are 2 L steel tanks and I use them in salt water where I drag a 40cf bailout. When I cave dive, I change them out for two AL19s so I can carry two LP95s as my bail outs (or two LP45s if I'm not going far).

Completely off topic and I'll start another thread, but I'm curious. If you are cave diving, obviously you need enough gas to get out with thirds. If you are rebreather cave diving, you need enough gas to get out from the place where your rebreather fails. But on an extremely deep push, you want a rebreather because you need the extended dive time a rebreather allows. So, if you are back 3 or 4 hours in a cave (say 3 for scrubber life), can you get out on 2 95's? Do you plan team bailout? I have nothing against team bailout, and I'm not trying to start anything, I'm just wondering what the protocol is for carrying bailout on long pushes.

 

[LiteHedded]

Completely off topic and I'll start another thread, but I'm curious. If you are cave diving, obviously you need enough gas to get out with thirds. If you are rebreather cave diving, you need enough gas to get out from the place where your rebreather fails. But on an extremely deep push, you want a rebreather because you need the extended dive time a rebreather allows. So, if you are back 3 or 4 hours in a cave (say 3 for scrubber life), can you get out on 2 95's? Do you plan team bailout? I have nothing against team bailout, and I'm not trying to start anything, I'm just wondering what the protocol is for carrying bailout on long pushes.

when you outrun the bailout you're carrying with you, that's the time to start diving over safety tanks staged in the cave

 

[Stoo]

That's why we like deco bottles that float when empty.

Priceless. I had one of those 45s escape my clutches once and it ended up in 140'. A friend recovered it the next day, but it still cost me a bottle of rum.

 

[The Chairman]

Do you plan team bailout?

Actually, yes. I'm a team diver in so much as I always carry enough gas for the "My, myself and I" team. I prefer to dive solo and always plan for being solo, even if I'm with others.

I am not an expedition caver. I have no desire to be an expedition caver. I know how far in I can go with thirds on two LP95s, so I can add a bit to that, but not so much that I don't have enough to do my deco. In fact, I don't mind limiting my dive to using just the two LP45s.

 

[northernone]

That's why we like deco bottles that float when empty.

Glad of this fact 4 days ago on a rental al80. Now while still feeling like an idiot I realize I'm in good company.

After clearing deco asking captains at the marina and a tip rectified the situation.

 

[tbone1004]

Completely off topic and I'll start another thread, but I'm curious. If you are cave diving, obviously you need enough gas to get out with thirds. If you are rebreather cave diving, you need enough gas to get out from the place where your rebreather fails. But on an extremely deep push, you want a rebreather because you need the extended dive time a rebreather allows. So, if you are back 3 or 4 hours in a cave (say 3 for scrubber life), can you get out on 2 95's? Do you plan team bailout? I have nothing against team bailout, and I'm not trying to start anything, I'm just wondering what the protocol is for carrying bailout on long pushes.

at 100ft, 0.7cfm SAC, 50fpm kick speed, and 1.5x safety factor, cave filled 95's can theoretically get you out from 4500ft. This is a rather conservative number since in an emergency you'll probably be moving a bit faster than 50fpm, and the average depth of most of the tourist caves isn't 100ft, but closer to 80ish, but that is the number I would personally use.
4500ft is a LONG way back, and well into the range that you should be using a DPV because of the decompression obligations. That's ~180 minutes of bottom time which is going to give you probably 90 minutes of deco. That's quite a long dive, so the need for anything more than that necessitates scooters and proper dive planning