Done a little research, figure this is a good place to fill in the gaps

[Sinbad the Diver]

I have begun the process of considering the option of looking into buying tanks... yes I have commitment issues.

I am in the middle of the AL vs Steel debate. I have heard the advantages of steel (more air, smaller size, use less weight) and I have to see where I come in on those factors compared to the price difference.

The one thing I have discovered that I would like to have confirmed is the Yoke vs DIN piece. One of the places I looked said that you have to use a DIN to use preasure over 3,100#, the value of steel being more air in less space if you can't get the more air part, not sure of the value. Did I read that right? If so, since my reg is a Yoke, can it be switched to a DIN? The answers to these questions could make my decision real easy.

You can tell by the question that I am new at this so any input would be appreciated.

 

[PhilEllis]

......The one thing I have discovered that I would like to have confirmed is the Yoke vs DIN piece. One of the places I looked said that you have to use a DIN to use preasure over 3,100#...........

In the United States and Canada, any cylinder with an operating pressure of 3442 PSI or less can support a yoke clamp valve. Most steel cylinders will now come with an "international valve", which allows the use of a DIN or a yoke connector. The screw-in insert allows the valve to work with a yoke clamp....removal of the insert allows the use of a DIN fitting. Thanks.

Phil Ellis

 

[DeepSeaExplorer]

If it's your fist tank, get an AL 80 with a yoke valve because that's the tank you'll get when you travel / rent, and not all dive shops have DIN adapters, or high pressure air. They're more cost effective in the long run and easier to resell if you need to unload them. Everyone, no matter what kind of diving you do, needs a few AL 80s around.

 

[Teamcasa]

The only real advantage of an aluminum tank is price. A steel tank is superior by any other measure.

The convertible DIN/Yoke valve is a must for me, all my regs are DIN. I have two AL80’s (with new valves), one HP100 and one HP80. The AL tanks almost never get any use other than as a second tank where fills are not convenient.

 

[Sinbad the Diver]

Thanks, that was very helpful, but now that I've started thinking about it I might actually be more confused.

It's been a lot of years since I took a physics class, so please forgive my ignorance.

In the end the goal is to provide the air to maximize bottom time. There are other factors that are impacted by the weight of the tank boyance full vs empty, depth, SAC rate, etc. But all else being equal, how do you calculate the difference in available gas between tanks of different sizes and preasures. I would assume that if you have an 80 at 3.4K# you get more gas than if you have an 80 at 3K#s. Correct?

I see a lot of people with smaller steel tanks (72s). How does a 72 at 3.4K# compare with an 80 at 3K#?

My head hurts....who knew I was going to have to relearn physics for ths. Dr Ently would be very hurt that I don't remember any of this. Any recomendations for a good general overview of this. I'm doing the pre-reading for the SDI deep course and it layed out a chart of sizes, preasures and weights, but I should probably understand the relationship and what it means.

 

[diver 85]

I have begun the process of considering the option of looking into buying tanks... yes I have commitment issues.

I am in the middle of the AL vs Steel debate. I have heard the advantages of steel (more air, smaller size, use less weight) and I have to see where I come in on those factors compared to the price difference.

The one thing I have discovered that I would like to have confirmed is the Yoke vs DIN piece. One of the places I looked said that you have to use a DIN to use preasure over 3,100#, the value of steel being more air in less space if you can't get the more air part, not sure of the value. Did I read that right? If so, since my reg is a Yoke, can it be switched to a DIN? The answers to these questions could make my decision real easy.

You can tell by the question that I am new at this so any input would be appreciated.

wrong on the 3100# thingy----I dive a yolk on HP 120's(3500 starting pressure) all the time......

 

[Teamcasa]

Don’t over think it. Unless you have your own compressors, fill pressures are what they are, where you get them. Most shops have no problem filling my HP100 to 3500 PSI.
The two main advantages to a steel HP100 vs AL80 is that the HP100 is 100 cuft and negatively buoyant at 500psi. The AL80 only holds 77+- cuft of air and is 4 lbs positively buoyant at 500 psi.

So… When I switch from the HP100 to the AL80, I need to add an extra 4-5 lbs of lead to compensate of the buoyancy difference and I get less air.


HP100
Empty, 33lbs
Buoyancy Full,-10lbs
Buoyancy Empty -2.5lbs

AL80
Empty, 31.7lbs
Buoyancy Full, -1.9lbs
Buoyancy Empty, 4lbs

 

[Sinbad the Diver]

OK, thanks Teamcasa I see my major flaw....the capacity measurement is at the max preasure, not the internal volume of the tank as I was thinking.

The other thing I was missing was the size. I was assuming that an AL80 and a Steel 80 were the same size. I need to go back to metalergy 101.

Thanks to all, I'm much smarter now (or at least better informed). BTW...found this site which helped me understand this a bit better ¤ Scuba Tanks - The Scuba Guide

 

[Teamcasa]

Sinbad, here is another link for tank info. Dive Rite Express -- How to Select a SCUBA Tank

 

[eponym]

[snip] how do you calculate the difference in available gas between tanks of different sizes and preasures? I would assume that if you have an 80 at 3.4K# you get more gas than if you have an 80 at 3K#s. Correct? I see a lot of people with smaller steel tanks (72s). How does a 72 at 3.4K# compare with an 80 at 3K#?

For most tanks, the quoted size is the capacity at the rated fill pressure. For example, a high-pressure (HP) steel 100 holds 100 cu.ft. at its rated pressure (3442 psi) and temperature (70F?). The one exception to this sensible standard is the AL80, which actually holds 77.4 cu.ft. at its rated pressure (3000psi) and temperature (70F).

But yes, a fat fill (as it's usually called) can give you more air in a given tank. Some shops will ignore regulations and overfill. Some won't.

Here is an article with some more thoughts on the subject.

-Bryan