Why choose LP tanks over HP Steel tanks?

[JackD342]

Quoting myself from a different post:

For all those that "weighed in", so to speak, on aluminum versus steel and buoyancy, here is a reference document.
where I did the math on what changes if you move from an AL80 or an AL100 to another common aluminum or steel cylinder size. For this comparison I used current Luxfer and Faber specs. I have calculated the impact on your weighting, and on how much you carry on your back/waist out of the water. (extra 8 pounds on my back if I use my AL100s!) Of course, a cylinder from a different manufacturer will not be exactly the same, but this gives you a good general idea.

To my surprise, I found that a standard aluminum 80 requires more lead than any other cylinder in the comparison. If I am really bored some day, I may add Faber LP tanks to the table too and see what I find.

 

[Marie13]

I don’t know the specifics of the problems with LP fills. All I know is I was told people had issues getting them filled. That’s all.

 

[Bob DBF]

Got interested in this along the way and figured I'd put it togather before I chimed in with my perspective.

Higher pressures put more stress, wear, and tear on your regulator. Same reason you turn your air on slowly rather than quickly.

First, any HP air should be turned on slowly because of the possibility of injury producing leaks, physical damage to equipment, and the possibility of diesel ignition.

They don't.
You don't, unless your regulator is not all intact.

You know, I hesitated before typing out the wear and tear comment, but decided it should be out there. I wish I had a solid source...

Thanks for the conversation. I've been noodling on this as well. Here's a source:
How to Select a SCUBA Tank | Dive Gear Express®

Regs now are made for HP air, 300 bar in most cases, and that pressure would be what the design engineers would consider as normal wear and tear for maintenance cycles. Considering that, a lower pressure might stress the equipment less and produce less wear and tear, but is irrelevant if you follow the recommended maintenance.

I take my perspective from what the equipment is designed to do.


Bob

 

[Billy Northrup]

Well in South Florida, unless your at a tech shop your going to get 3000 psi no matter what your tank rating is. I learned quickly to ditch my HP's because I get a nice overfill instead of an under fill without the hassle. Never a problem when running mix because the people are dialed in who do that.

 

[boulderjohn]

Well in South Florida, unless your at a tech shop your going to get 3000 psi no matter what your tank rating is. I learned quickly to ditch my HP's because I get a nice overfill instead of an under fill without the hassle. Never a problem when running mix because the people are dialed in who do that.

You and I have had very different experiences getting fills in South Florida--which is what I described above (post #23).

 

[Diving Dubai]

I'm still confused between LP and HP tanks, please educate me

I obviously live in metric land, where Al is filled to 207bar (3000psi) and Steels to 232 (3364psi (ish) For Ali we have the usual candidates AL 30,40 and 80, (yes we sometime refer to them in their CU ft size) then Steels, 10, 12 & 15 which roughly translate as far as I can figure @3442psi to HP85, HP100 &HP120 respectively

Where did the LP and HP difference come from?

Why would you use LP? (I'm presuming that an LP 85 is larger than an HP85?)

Is it just filling pressures or are there other benefits?

Genuinely interested

 

[MichaelMc]

I'm still confused between LP and HP tanks, please educate me

In the US we have
- LP: 2400 psi tanks, certified for 10% over fill (2640) if they got a plus rating at hydro.
- HP: 3442 psi tanks, not certified for any over fill.

Current LP tanks are closer to neutral than HP, which can be nice for sidemount if you don't need much lead.

The spec under which LP tanks are certified makes their rating more conservative than that of HP tanks, suggesting some additional overfill would be sound from an engineering stand point.

Edit: HP - High pressure, LP - Low pressure....
Plus aluminum tanks usually to 3000, and some old steel 72 tanks to 2250.
More details on the above difference in specs:

Most LP tanks are based on the DOT 3AA specification which is very conservative. HP tank specifications represent exemptions to the 3AA specification and as a result, allow service (working) pressures that amount to a slightly higher percentage when compared to burst pressures. There is ample anecdotal evidence regarding the safety of "Cave Filling" (50% overfill) LP cylinders. In reading one manufacturer's exemption specifications, it appears that their HP cylinder could sustain a 35% overfill and not exceed the same percentage of overfill to burst pressure that seems to be common on LP cylinders in 'Cave Country'. Of course, overfilling any cylinder means operating outside of the design parameters and accepting its concomitant risk. I do not recommend the deliberate overfilling of any cylinder. I also do not get too concerned about a slight overfill that cools to service pressure, nor do I get too concerned about a properly filled cylinder that lies on hot asphalt and rises to uncomfortable levels. Again, I do not recommend deliberate overfilling of any cylinder.

 

[EireDiver606]

What does HP mean? High pressure? 300 bar? Very confused by this American terminology...

 

[boulderjohn]

In the American system, a scuba tank contains a specified amount of gas when it is filled to its service pressure. If it is filled to less than its rated pressure, it has less gas; when it is filled to more than that pressure, it has more gas. Low pressure tanks have rated pressures around 2400 PSI. High pressure tanks have rated pressures around 3442 PSI.

As an example, my LP 108s will be filled to 108 cubic feet of gas if they are filled to 2640 PSI. If I fill them to 3,000 PSI, they will have about 120 cubic feet. In contrast, an HP 120 will not have 120 cubic feet in it until it is filled to about 3442 PSI. If it is filled to only 3,000 PSI, it will only have about 100 cubic feet in it.

 

[Diving Dubai]

In contrast, an HP 120 will not have 120 cubic feet in it until it is filled to about 3442 PSI. If it is filled to only 3,000 PSI, it will only have about 100 cubic feet in it.

That's obvious.

So my question to that would be, is there a huge difference in what pressure shops will fill to (to justify LP over HP) in the US?

Every-where I've been Ali's get filled to 200-210bar and those holiday op's offering steels fill them to 240..

If some handed my a tank with 2400 (165) they'd get a Paddington stare....