LP vs HP tanks on doubles...

[iztok]

I don't believe I mentioned any pressure of 3860psi.

You are right.

Superlyte27 mentioned it and sean_nc quoted it in his response and you quoted sean_nc in your statement. (about "magic fills")

So if I had a choice between filling LP95 to 3860 or HP119 to 3860psi I would chose the later.

Overfilling LP to 3860 is overfilling by 46% while overfilling HP to the same pressure is only 12% overfill.

 

[DA Aquamaster]

The test pressure on a 3442 psi special permit tank is 5163 psi (3/2 times the service pressure).

The test pressure on a 2400 psi 3AA steel tank is 4000 psi, 5/3rds the service pressure.

So yes, If I am going to fill a tank to 3860 psi, I'd rather fill the 3442 psi tank.

On the other side of the coin, the 3AA engineering standard has been around a long time, is not as dependent on proper heat treating, is massively over engineered and the tanks have a long record of successfully withstanding overfills to 3600 psi. In comparison, everyone is a lot less sure how well the special permit steel tanks will hold up over the long term.

 

[EzeeDiver]

I feel your pain as well. I just moved into tec, and here is what I did...

2- LP 95 (yes, advised from Florida cave country instructor)
2- AL 80 (recommended for deco gas)
[only 4 tanks I own]

As opposed to putting together doubles, I am sidemounting them, either the AL80s or LP95s. From someone who never used two tanks before, this made the transition and horizontal trim very easy. Other nice thing is that since all tanks are left as singles, I can choose any tank I want based on the diving I'm doing. Even if I'm doing a rec dive with my single tank BC, I will typically choose one of the LP95s if in a drysuit (not as much weight needed), or an AL80 if diving wet.

I have been diving with these tanks since January, and am pleased with the different configurations I can make up. Also, the sidemount configuration makes toting the tanks around a lot easier, just one at a time. Lots easier on the back...

Just a suggestion to check out to see if you can take your tec class from a sidemount instructor in your area, and possible even check out the PADI sidemount class. Again, made transition to tec a breeze. That way, you can just use the tanks you have and fill them however you want, and have many configurations available to you. Just a thought...happy diving!

 

[UCFKnightDiver]

PADI has a sidemount class? lol

 

[sean_nc]

Find me an HP tank that holds in excess of 130 cuft of gas and I will, and it has been happening for years with no failures and tanks are still passing hydro's with no problem, not seeing the issue here.

Yea, it's that whole "I've never had a problem" attitude that I don't get. If you want more why don't you just take that 130 and overfill it to 5163psi? ...lots of gas if it holds together. (2400 overfilled to 3600=1.5 3442 overfilled by 1.5=5163) You'll get away with it a certain number of times but I don't want to be around.

DA has a great point about test pressures and I understand the issues with different (maybe less tested) materials.

What I don't understand is why not use the newer materials that are rated for what you're trying to do. Why overfill a 95 when you could just rated fill a 119?

 

[Meng_Tze]

.. Why overfill a 95 when you could just rated fill a 119?

Usually this comes down to physical size, weight, price and buoyancy characteristics.

 

[DA Aquamaster]

Usually this comes down to physical size, weight, price and buoyancy characteristics.

I wish that were true, but in many, even most cases, individual divers have not thoroughly researched the size, weight, price and buoyancy issues. Instead it often comes down to diving a tank because of adivce they got from someone else, and that advice may or may not be accurate or all that credible.

If people really looked at a Worthington X8-119 or an X8-130 compared to a Worthington LP 95, Worthington would sell damn few LP 95s.

 

[PfcAJ]

Yea, it's that whole "I've never had a problem" attitude that I don't get. If you want more why don't you just take that 130 and overfill it to 5163psi? ...lots of gas if it holds together. (2400 overfilled to 3600=1.5 3442 overfilled by 1.5=5163) You'll get away with it a certain number of times but I don't want to be around.

DA has a great point about test pressures and I understand the issues with different (maybe less tested) materials.

What I don't understand is why not use the newer materials that are rated for what you're trying to do. Why overfill a 95 when you could just rated fill a 119?

There has never been a problem, therefore, it just isn't a problem. And as mentioned before, filling past a certain pressure results in diminishing returns, and only serves to stress your equipment. There just isn't a reason to go higher. If tanks started exploding tomorrow from 3600psi fills, I'd stop diving lp tanks. I have a set of 104s from the 80s that just passed hydro, and they've seen some interesting pressures.

For real diving, lp104s/hp130s ( or lp120s for really big dives) to 3600 is the limit of the amount of gas I want to carry in one basket, anyway. If I need more than that, its time for stages.

 

[pernicia]

The REAL HP tanks are 3500psi (stamped on the neck) w/ 7/8 valve.
The new "HP" tanks are rated 3442 psi which in reality they are a LP tank with a DOT exemption. That explains what "DA Aquamaster" mentioned before.

From the Fill Express/Dive Gear Express Website...
X-Series Steel SCUBA Tanks by Worthington Cylinders - Dive Gear Express

Many experienced divers have preferred low-pressure cylinders because they are easier on regulators, have no short-fill concerns, and are more suitable for partial-pressure blending. More recently, the low-pressure 3AA cylinders (2640 psi, i.e., 2400 with a +) are being replaced by the new DOT exemption cylinders (3442 psi, no plus needed). That's because you can use the high-pressure 3442 psi cylinders as low-pressure 2650 psi cylinders if you prefer, simply by under filling. The 3442 psi DOT Exemption cylinders have the same length, diameter, and capacity at lower 2640 psi pressure as the 3AA cylinders. Even better, the empty weight of the new cylinder design has been reduced slightly, yet the buoyancy remains slightly negative when empty.

Cylinder...............2640 psi....3000 psi....3442 psi

X7 Steel 80...........64 cu. ft.----72 cu. ft.----80 cu. ft.
X7 Steel 100.........80 cu. ft.----89 cu. ft.----100 cu. ft.
X7 Steel 120.........96 cu. ft.---107 cu. ft. ---120 cu. ft.
X8 Steel 119.........95 cu. ft.---107 cu. ft.---119 cu. ft
X8 Steel 130........104 cu. ft.---117 cu. ft.---130 cu. ft.

 

[DC53]

I wish that were true, but in many, even most cases, individual divers have not thoroughly researched the size, weight, price and buoyancy issues. Instead it often comes down to diving a tank because of adivce they got from someone else, and that advice may or may not be accurate or all that credible.

If people really looked at a Worthington X8-119 or an X8-130 compared to a Worthington LP 95, Worthington would sell damn few LP 95s.

NOW THAT's FOR SURE! I have been absolutely AMAZED at how even the very experienced divers INCLUDING ADVANCED INSTRUCTORS that I have spoken to seem to have NO IDEA of the actual specifics, for example, the weights of various sized tanks, actual measured underwater bouyancy full and empty. It's almost impossible to have a real discussion based on specifics as opposed to their idea of conventional wisdom.... When I ask a question and quote a weight of a couple of given tanks (empty with valve), for illustration, 9 of 10 will go "HUH!? Oh I don't know about that but I know that (such and such) tank is better". So I ask, "Well, what makes it better, actually?" An answer for example was, "I just know they are better. I don't know where you get your numbers from but I know my Faber LP95 has got to be lighter than that HP 100 youre talking about." It's as if that I as a relatively new diver with only 130 dives could not be in a position to challenge or question the isses. At least that's what if feels like. That's why I posted the question here; I am very inpressed to get all of the detailed knowledgable responses... Even though they don't always agree, most of them are backed up by facts and explanation. THAT is usable to me.. Thank you.