Tank math?

[RDP]

I am in the process of determining which tank to buy. I have a peference for steel.

I am not fully understanding tank capacity. I read about low pressure tanks and high pressure tanks of the same size holding different amounts of gas. What is the formula? Pro's and Con's?

Size? I am looking at an E7-80. It seems short, light (28lbs.), & -2.5 bouyancy empty. I dive mostly cold water and could stand to lose a few pounds off the belt.

Suggestions???

 

[yknot]

Suggestions???

Yes. Use the forum search function. Start with any of the LP vs HP, steel vs aluminum threads. If you still don't see an answer, look again.

 

[scubasean]

I am in the process of determining which tank to buy. I have a peference for steel.

I am not fully understanding tank capacity. I read about low pressure tanks and high pressure tanks of the same size holding different amounts of gas. What is the formula? Pro's and Con's?

Size? I am looking at an E7-80. It seems short, light (28lbs.), & -2.5 bouyancy empty. I dive mostly cold water and could stand to lose a few pounds off the belt.

Suggestions???

An 80 holds 80 cu ft at its rated pressure...A 100 holds 100 cu ft at its rated pressure...

The rated pressure could be 2450 (which would mean it is an LP tank) or 3450 (which would mean it is a HP tank) or something in between...

An LP tank would have different buoyancy numbers than an HP tank holding the same amount of gas, each at their rated pressures.

 

[JimC]

Tank Specs:

Internal Volumn: The size of the inside of the tank, ususaly expresed as liters and uses in Europe: ei a 12l tank is a tank with an internal capacity of 12 liters.
Rated Presure: The fill presure which a cylinder is rated to. Usualy in PSI or Bar.
Volumn at Presure: The volumn of air, as mesured at 1atm, that a tank holds when filled to service presure. Ei: an 80 cf tank holds 80 cf of air when at 1atm (temperature ignored). Typicaly used in North America.

Some examples:

AL80: ~11 liters, 3000 psi, 77.4 cf
PST E7-80: ~9.5 liters, 3442 psi, 80cf

PST LP 80: ~12 liters, 2540, 80cf
PST E7-100: ~12 liters, 3442 psi, 100cf

PST LP 104: ~16 liters, 2640 psi, 104cf
PST E8-130: ~16 liters, 3442, 130cf

You can see that a smaller tank at a higher presure can hold the same amount of gas. You can also see that tank the same size at a higher presure can hold more.

I personal LOVE the E7-100 for recreational diveing. Its a touch shorter than an AL80, its more negative and about the same weight. You also get an extra bunch of gas, and even a hot and fast fill leaves you with buckets of gas for most dives.

 

[RDP]

Yes. Use the forum search function. Start with any of the LP vs HP, steel vs aluminum threads. If you still don't see an answer, look again.

I searched and read past threads about this before I posted.

I understand a 80cf tank holds 80cf. What I am looking for is the formula regarding pressure and capacity (in the form of volume.

Thanks for the info JimC.

 

[Boogie711]

It's really simple dude - at it's rated pressure, a tank holds that particular amount. Since pressure is variable, that will tell you a lot about a particular tank size.

An E7-80 will be tiny, but chances are good you won't get 80 cf of gas - since you need to jack it up to 3442 psi to get to it's "rated pressure."

An E7-100 is still smaller than an AL80, but at 3000 psi holds 13 extra cf of gas. (90 cf vs. 77.3 cf.) At it's rated pressure of 3442, it will hold the full 100 feet. On the other hand, something like an LP-95 will hold 95 cf at 2640 psi, and if you jack it up to 3000 psi will hold considerably more.

To come up with a 'tank rating', just take cubic feet (100) and divide by rated pressure (3442). To make it easier on yourself, then multiply by 100. For an E7-100, this number is 2.9, but for an E7-80 it's only 2.3. For an LP120, it's a whopping 4.5.

 

[RDP]

It's really simple dude - at it's rated pressure, a tank holds that particular amount. Since pressure is variable, that will tell you a lot about a particular tank size.

An E7-80 will be tiny, but chances are good you won't get 80 cf of gas - since you need to jack it up to 3442 psi to get to it's "rated pressure."

An E7-100 is still smaller than an AL80, but at 3000 psi holds 13 extra cf of gas. (90 cf vs. 77.3 cf.) At it's rated pressure of 3442, it will hold the full 100 feet. On the other hand, something like an LP-95 will hold 95 cf at 2640 psi, and if you jack it up to 3000 psi will hold considerably more.

Okay, I think I'm getting it. Thanks for the response.

 

[RDP]

A good link for this info.

http://www.diveriteexpress.com/library/tanks.shtml#alumsteel