HP or LP double

[PerroneFord]

XS Scuba,

Can you speak to the buoyancy charactistics of the X8 130 tank? This is the only tank which might hold enough gas for my purpose. Similar tanks from other manufacters place me on my head even with the bands pushed right up to the shoulder of the tank. The LP108 has a center of buoyancy that is nearly perfect for me.

While available gas in the cylinder is important, more important is the ability to actually DIVE the things.

Thanks for your thoughts.

 

[lamont]

Therefore it's just as "safe" to fill an aluminum tank to hydro as steel.

Aluminum cracks faster than steel.

I understand they're tested to the same degree and that two tanks that pass hydro should still have the same characteristics when overfilled because they all pass the same 10,000 cycle LBB test, but there's no track record of overfilling Al tanks, there is a track record of neck cracks causing Al tanks to not fail in LBB, and the metallurgical difference in cracking is not comforting...

YMMV...

 

[PhilEllis]

I had a good sense about you when you were going through that B.S. in the spring, and I'm glad I spent money with you and your shop. We need more vendors like you.

But, my friend, you aren't spending enough! You gotta give to the Phil Foundation at LEAST once a week! Thanks.

 

[limeyx]

Spratman,

Here's the problem.

Lets say I buy a LP95 and you buy a HP100. We are in say Boston. They will fill both of our tanks to rated pressure. I get 95cuft, you get 100.

We go to NYC, they have a 3000psi compressor. They are willing to overfill my tank. Now I get 107cuft and you get 85.7.

Now we come to N.FL. to dive the springs. They have a 3500psi compressor. They give us both 3500. I get 126cuft, you get 101.

The only instance in which you get more gas than me is if we are at a shop with a compressor that can push 3500psi AND they are not willing to overfill me. In that instance, I get exactly what I paid for.

Your example is misleading. You are comparing apples and oranges.

Run the same comparison with an LP95 and HP-119 which is essentially the same physical size as the LP95.

 

[PhilEllis]

Aluminum cracks faster than steel.

I understand they're tested to the same degree and that two tanks that pass hydro should still have the same characteristics when overfilled because they all pass the same 10,000 cycle LBB test, but there's no track record of overfilling Al tanks, there is a track record of neck cracks causing Al tanks to not fail in LBB, and the metallurgical difference in cracking is not comforting...

YMMV...

If I am not mistaken (don't have the standard in front of me) I think the failure after 10,000 cycles must be "controlled and non-catastrophic" in nature. Given that, I think the relative metallurgy and the speed of the failure is not significant. What is significant is that there is no "explosion". Again, my view.

Phil Ellis

 

[cerich]

HP130s are the same physical size / water volume and are rated to 3500 psi. All other things being equal the HP tanks are hands-down better than the LP tanks. Where things are not equal are that some people prefer the bouyancy characteristics of the LPs, the LPs are cheaper, and nothing (with reasonable buoyancy characteristics) can beat a jacked up LP120...

Hi Lamont,

Normally HP refers to cylinders that are 2500 psi like the Genesis, the new exemption tanks are very close in pressure but not really "HP" tanks, they still use standard valves and yoke fittings are common.

The 130 Exempt are similar to 108 LP but not 130's HP, follow?:huh:

 

[cerich]

If I am no mistaken (don't have the standard in front of me) I think the failure after 10,000 cycles must be "controlled and non-catastrophic" in nature. Given that, I think the relative metallurgy and the speed of the failure is not significant. What is significant is that there is no "explosion". Again, my view.

Phil Ellis

To the tanks or the poor guy filling it?

 

[PerroneFord]

Your example is misleading. You are comparing apples and oranges.

Run the same comparison with an LP95 and HP-119 which is essentially the same physical size as the LP95.

Well, I've never heard math called misleading.. but ok. I selected tanks that at rated pressures have nearly the same capacity. For dive planning, in order to not do dissimilar cylnder calcs, it's helpful if everyone is working with the same VOULME of tank. Who cares what physical size the tank is?

But I'll humor you:

First example, I get 95cuft, you get 119.

Second example I get 108 you get 104

Third example I get 126 you get 121

Again, the math proves out that the ONLY instance you get more gas is when the shop CAN fill you to 3500 and they refuse to overfill me.

So what was your point?

 

[PhilEllis]

To the tanks or the poor guy filling it?

LOL. I assume it means to the tank. No matter how you instantly release an extra 80 or 100 CF of air into a room (that is already full of air), the poor guy filling the cylinder is not going to like it. But the room temperature will certainly drop a few degrees.

Phil Ellis

 

[PerroneFord]

But the room temperature will certainly drop a few degrees.
Phil Ellis

Drop?

If the room held together, I'd think compression of gas in an enclosed space would raise the temp...