Aldora Tanks

[divingjd]

Aldora's tanks are high-pressure steel tanks, 3500 psi operating pressure, regularly filled between 3300 and 3500 psi. Those HP steel 100s pack significantly more gas than an aluminum 100. Standard operating procedure at Aldora is to give men 120s and women 100s. Adjustments can be made after you see how it works and they see how you do. I've seen a few men who do great with the 100s. The extra gas allows very long dives. The divemasters lead the dives accordingly. 80 minutes is not a particularly long dive with Aldora, particularly on a nitrox boat.

 

[uncfnp]

Those HP steel 100s pack significantly more gas than an aluminum 100.

Hi divingjd. Could you explain this in a bit more detail please?

 

[Gdog]

Another thing I havent seen mentioned yet, the steel hp tanks trim out very nicely. I would take the steel tank over the aluminum any day. I sold all 4 of my al80 tanks here at home, was happy to get rid of them and take a few pounds off my weightbelt. I now have steel hp 100s, and steel hp119. The hp 100 trim out very well, very nice to dive.

 

[Gdog]

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan
A nice reference chart..

 

[ggunn]

Those HP steel 100s pack significantly more gas than an aluminum 100.

Not if they are both filled to their normal working pressure. 100cf is 100cf no matter where it comes from.

 

[uncfnp]

Not if they are both filled to their normal working pressure. 100cf is 100cf no matter where it comes from.

Agreed (post 28) and that was kinda my point. There can be minor differences, esp. with the 80's but I think the most is about 3 cf even then.

 

[divingjd]

Looking at the specs chart Gdog posted, I may have been wrong in saying that the steel 100s carry a lot more gas. I have never used an aluminum 100. I had assumed an operating pressure of 3000 psi, like the standard AL 80. It appears that the AL 100s have an operating pressure of 3300 psi, so that's only 200 psi less than the HP steel 100s Aldora uses. The HP steel 100s, at 3500 psi, would carry more gas than an AL 100 at 3300 psi, but not a lot more. 100 cf is 100 cf at the same operating pressure, but 100 cf at a higher operating pressure is more gas. An HP steel 100 holds more gas than an AL 100, not because it's steel, but because it has a higher operating pressure. Sorry for the confusion.

 

[uncfnp]

Looking at the specs chart Gdog posted, I may have been wrong in saying that the steel 100s carry a lot more gas. I have never used an aluminum 100. I had assumed an operating pressure of 3000 psi, like the standard AL 80. It appears that the AL 100s have an operating pressure of 3300 psi, so that's only 200 psi less than the HP steel 100s Aldora uses. The HP steel 100s, at 3500 psi, would carry more gas than an AL 100 at 3300 psi, but not a lot more. 100 cf is 100 cf at the same operating pressure, but 100 cf at a higher operating pressure is more gas. An HP steel 100 holds more gas than an AL 100, not because it's steel, but because it has a higher operating pressure. Sorry for the confusion.

Hopefully one of the tank gurus will join in but its not just the operating pressure that counts but the volume of the tank and the pressure. Yes, the working pressure of a HP steel is greater then an alumnium but the volume is actually smaller, hence the tanks themselves are smaller. The higher working pressure is what gives the stated capacity. So while a 100 cf steel tank is actually smaller than its alumnium cousin, the higher working pressure matches the capacity. Either "overfilled" will gives a higher cf of gas then the listed volume.

 

[divingjd]

Looks like you've made me go learn (or relearn) something. Thanks.

 

[boulderjohn]

For some reason, this is a very difficult concept for people to understand. I remember teaching a DM class where all the students were baffled about the differences in tank capacities and pressures.

I don't consider myself a tank guru, but uncfnp is correct. A tank has the amount of gas advertised when it is filled to its rated pressure. If an HP 100's rated pressure is 3500 PSI, it will have 100 cubic feet when it is filled to 3500 PSI. If an AL 100 has a rated pressure of 3300, it will have 100 cubic feet when filled to 3300 PSI.

Where people get confused is when dissimilar tanks are filled to the same pressure. Let's say you have three tanks, all the same advertised capacity (100 cubic feet), and all filled to 3000 PSI. The LP tank (rated at 2640) will have the most, well over 100 cubic feet, because it has been filled over 10% more than its rated capacity. The AL tank (rated at 3300) is filled at about 10% less than its rated capacity, so it has a lot less. The HP tank (rated at 3500) will have the least, because it is filled to about 15% below its capacity.