which is better Lp or HP steel's

[Rev. Blade]

drbill once bubbled...

How could an LP104 at 3000 psi have more air than a HP120 at 3200-3300 psi? I will admit that psychics was my worst subject but this doesn't seem to make sense.

I dive HP120's or HP100's all the time.

Dr. Bill

Well you shouldn't have taken your physics instruction from a psychic.

OK. I'll take a quick stab at the subject... I'll be simplifying the math, so please don't bother with saying I'm wrong. I know this is wrong. I also know it's nearly right, and is simpler than the scientific versions:

Americans measure tanks by how much air they would hold at their maximum rated pressure. (Europeans measure the tanks based on how many liters of water they hold.) A LP104 was designed to be filled to about 2600 psi.
3000/2600*104=120

 

[Braunbehrens]

Uncle Pug once bubbled...
a HP120 has 120cf at 3500 psi but only 113cf at 3300 psi.

a LP104 has 104cf at 2640 psi but 118cf at 3000 psi.

The nice thing is that the 104 has about 130cf at 3800!

Shhhh. Don't tell anybody ;-)

Actually I just got a couple of HP tanks hydroed, and was talking to the guy at the hydro facility. He said those tanks would easily hold 10 000 psi. He also showed me some O2 bottles they were dealing with. You would not believe how these bottles looked, it made the inside of my tanks (which had a little rust) look like an operating room. Then he showed me a tank they had to fail. The entire inside of the tank was covered in black gunk, and pitting isn't even the word for it, potholed more likely. The amazing thing is that this tank had been in use!

Anyway, this made me relax quite a bit about my tanks.

BTW, is the new thermo valve with the insert a 5 thread or 7 thread? All the ones I've seen are 5 thread...which I don't like (probably out of pure paranoia).

 

[LUBOLD8431]

Braunbehrens, I will count the threads today and get back to you./ They are good for up to 230 bar (3442 psi). NO fear...

 

[Braunbehrens]

Thanks. I don't know how it happens, but sometimes the tanks I use get overfilled somehow...I like to have lots of threads

 

[otobmark]

I have OMS (Faber) LP's, mostly 112's (on sale of course). I was told that the newer 230 bar tanks from Faber are the same as mine, just that they retested them to certify for higher pressure. I routinely pump mine to 3,500 psi. When not using my normal LDS (who have on occasion pumped higher for really deep tech dives--proper burst disks etc.) I can still almost always get them filled to 3,000 even at resorts etc. I like the 5 thread valves because if I have to use a yoke reg I can use the screw in adapters. I need to find out for sure but, my guess is that the main reason for the 7 threads in the 300 bar valves is just to prevent attaching improper regulator, not because it is needed to hold the pressure. By the way, my LDS is not reckless, they did a great deal of research on the subject, things such as how many times you have to cycle the cylinder and at what pressures to fatigue the steel. Even so, I don't find the personal need to go to 4k nor am I recommending others doing what I do. I do however, recommend LP tanks or the new "intermediate" e series. If you travel, all you can usually count on is 3,000 psi used to fill thoses gazillions of AL80's.

 

[jonnythan]

Uncle Pug once bubbled...
a HP120 has 120cf at 3500 psi but only 113cf at 3300 psi.

a LP104 has 104cf at 2640 psi but 118cf at 3000 psi.

The LP104 also weighs 10 pounds more, is another 3/4" in diameter, and probably won't get filled to 3000 by your LDS.

edit: the point is well taken, but it isn't the whole story

 

[Dryglove]

jonnythan once bubbled...
and probably won't get filled to 3000 by your LDS.

I have a heck of time trying to get the dive shops to give a proper fill to 2640psi. After cool down they mostly end up at 2400 to 2600 psi depending where i get them filled. I got excited once cause i got a nitrox fill to 2700 psi and that was only cause they screwed up when doing the partial pressure fill.

Its discouraging when you walk into the dive shops and they have big signs on the wall stating they will not over fill your tanks so dont ask. Maybe its a CA thing.

 

[LUBOLD8431]

So, I just counted the threads and there are FIVE.

 

[LUBOLD8431]

I wouldnt be scared about using those valves with 3442. They can hold the pressure. IF however, you dont like that valve, you can order the cylinders in with a 300 bar DIN for an additional $20.

 

[Braunbehrens]

Thanks Lubold

Hey lal, where in Central CA are you trying to get fills?