Hydrostatic testing and serviceable life of tanks

[happy-diver]

Yes you don't buy aluminium tanks for your back as everything about them is just crap

 

[OTF]

Yes you don't buy aluminium tanks for your back as everything about them is just crap

I wish someone told me this when I started buying tanks. They're good for stage bottles or warm water diving though.

 

[-JD-]

@hawkdoc60 I'm going to echo the advice of some others and say that you are likely better off with steels for diving around here.

An HP100 will give you 30% more air (as long as you get fills to working pressure on both, but still 10% more if only filled to 3000psi). They are also a couple inches shorter than an AL which is handy at times.
HP100s are about 3 lbs heavier for dry handling, but their buoyancy characteristics mean that you can drop 5lb of lead vs an AL80. This leaves you slightly lighter in total (or just a bit more with way more air in an HP120) and generally more comfortable and better trimmed because of the weight distribution.
The calculus may be different if you are diving in warm water without buoyant thermal protection where some folks may need minimal or no lead even with an AL.

This area has a bunch of older Sherwood Genesis (PST manufactured) HP tanks floating around that have 3500psi service pressure and use a smaller diameter valve thread (7/8") vs newer HP tanks that have a 3442psi service pressure and use larger, "standard" (3/4" - they are a different thread standard, thus the oddity). There is nothing wrong with the older 3500psi tanks (all 10 of mine are) BUT the 7/8 valves are essentially ONLY available with 300 bar DIN regulator connections. The 3442psi tanks allow you to use DIN or newer yoke valves with convertable valves.

There are also a ton of low and medium pressure steels around with a broad range of characteristics.

Feel free to reach out if you decide to go the steel route. Happy to have a conversation to hit some high points and then direct you to some of the more detailed threads so you can go down the rabbit hole.

I'm not quite sure when I'll be out there again, but my parents are in Terre Hill. I could bring out sample AL80 and PST HP100 & HP120 if it is helpful.

 

[hawkdoc60]

@hawkdoc60 I'm going to echo the advice of some others and say that you are likely better off with steels for diving around here.

An HP100 will give you 30% more air (as long as you get fills to working pressure on both, but still 10% more if only filled to 3000psi). They are also a couple inches shorter than an AL which is handy at times.
HP100s are about 3 lbs heavier for dry handling, but their buoyancy characteristics mean that you can drop 5lb of lead vs an AL80. This leaves you slightly lighter in total (or just a bit more with way more air in an HP120) and generally more comfortable and better trimmed because of the weight distribution.
The calculus may be different if you are diving in warm water without buoyant thermal protection where some folks may need minimal or no lead even with an AL.

This area has a bunch of older Sherwood Genesis (PST manufactured) HP tanks floating around that have 3500psi service pressure and use a smaller diameter valve thread (7/8") vs newer HP tanks that have a 3442psi service pressure and use larger, "standard" (3/4" - they are a different thread standard, thus the oddity). There is nothing wrong with the older 3500psi tanks (all 10 of mine are) BUT the 7/8 valves are essentially ONLY available with 300 bar DIN regulator connections. The 3442psi tanks allow you to use DIN or newer yoke valves with convertable valves.

There are also a ton of low and medium pressure steels around with a broad range of characteristics.

Feel free to reach out if you decide to go the steel route. Happy to have a conversation to hit some high points and then direct you to some of the more detailed threads so you can go down the rabbit hole.

I'm not quite sure when I'll be out there again, but my parents are in Terre Hill. I could bring out sample AL80 and PST HP100 & HP120 if it is helpful.

That would be amazing. I never discounted steel, but was only familiar with the aluminum ones because that was all I was introduced to in class. I try to keep an open mind. Let me know when you will be in the area and I would gladly arrange a meeting to check the tanks out.

 

[Bob DBF]

Yes you don't buy aluminium tanks for your back as everything about them is just crap

Except the price.

When I bought mine, two Als were the same price as one steel, it was over an hour to the ocean where there were no fill stations. I wanted two dives for each trip, and I had a very limited budget, it narrowed my choices. I have since been able to correct that choice.

 

[Wookie]

It isn't a "bad alloy", in many ways it's a far superior alloy. In almost every comparison between alloy 6351 and 6061, the 6351 is superior except for Maximum temperature, Mechanical.

Just not for pressure vessels.

 

[Bob DBF]

It isn't a "bad alloy", in many ways it's a far superior alloy. In almost every comparison between alloy 6351 and 6061, the 6351 is superior except for Maximum temperature, Mechanical.

Just not for pressure vessels.

Even then, they had a long, yet troubled, service life. Mine worked well for 25 or so years, I retired them because of ongoing service cost, dive shop policies, and the fact I wasn't using them much in favor of steel.

 

[Wookie]

Even then, they had a long, yet troubled, service life. Mine worked well for 25 or so years, I retired them because of ongoing service cost, dive shop policies, and the fact I wasn't using them much in favor of steel.

I had 25 or so in rental. I got rid of them when CGA said they needed to be filled in containment.

 

[OTF]

It isn't a "bad alloy", in many ways it's a far superior alloy. In almost every comparison between alloy 6351 and 6061, the 6351 is superior except for Maximum temperature, Mechanical.

Just not for pressure vessels.

EDIT: I was mistaken in the previous version of this post blaming metal fatigue from repeated load cycling, the issue with bad alloy tanks is sustained load cracking which is different. Sustained load cracking - Wikipedia

 

[-JD-]

- Deleted - Content was non-sensical as it was a response to now moderated content.