High pressure or low pressure tank

[mk706]

I believe what tbone was referring to was internal volume as measured in liters.

Lets compare Worthington steel cylinders at the same volume. How much gas would each tank hold at 3,000 psi?

Tank	Water Volume	Gas Volume @3,000 psi
HP100	12.2 L	87.1 cu.ft
LP85	12.8 L	96.6 cu.ft
HP119	14.8 L	103.7 cu.ft
LP95	14.8 L	108.0 cu.ft
HP130	16.0 L	113.3 cu.ft
LP108	16.8 L	122.7 cu.ft

To calculate cu.ft: (Fill Pressure in psi* Volume in cu.ft)/Service Pressure
Example, LP 95 @3600 psi has 134 cu.ft gas (95*3,600)/2,640

Service pressure for HP 3,442 psi, LP 2,640 psi

 

[Peter69_56]

I find it interesting the logic of creating a max fill pressure, then stating an overfill rating. Call me old school, but I obhore this logic. My feeling is it creates an attitude of "overfill is ok" under any circumstance. If I can overfill by 10%, maybe 15% is ok too etc etc

I like the the idea of a max rating, clear and simple, logical. KISS (keep it simple stupid). 232 BAR means exactly that, anything above that is exceeding the tank rating.

i know it's your system over there and what you have always worked to, but as an outsider I find it strange.

my thoughts anyway

 

[PfcAJ]

DOT isn't logical.

 

[tbone1004]

Peter, they did it because the 10% was factored into the design, and it has to be retested every 5 years for the overfill rating. If the metal starts to show signs of stress fatigue and isn't stretching properly, they remove the + rating so the tank will only be eligible for it's initial fill rating. Gives the bottles an extra few hydro cycles before they are junk. The LP tanks are so overbuilt though that cave country has been filling the 2400+ bottles to 3600psi for over 40 years and the tanks from the 70's are still passing hydro with the + rating.

 

[Peter69_56]

Peter, they did it because the 10% was factored into the design, and it has to be retested every 5 years for the overfill rating. If the metal starts to show signs of stress fatigue and isn't stretching properly, they remove the + rating so the tank will only be eligible for it's initial fill rating. Gives the bottles an extra few hydro cycles before they are junk. The LP tanks are so overbuilt though that cave country has been filling the 2400+ bottles to 3600psi for over 40 years and the tanks from the 70's are still passing hydro with the + rating.

yes I understand it all from a straight technical point of view, but struggle with the logic of following this methodology. There is nothing wrong with it from a technical point of view. It's the human factor and thought process which can lead to over pressurisation above sane levels (the Darwinian factor). I know we cannot stop the stupid, but often these less than ideal approaches lead the stupid into dangerous areas.

 

[tbone1004]

agreed, but so many years of this without a single incident and all of them passing hydro every 5 years means the pressure ratings were just too conservative, it was an industry standard and it is what it is. Like I said about, I own LP72's with a 2250 service pressure, fill to about 2800psi and that's it. The rest of my bottles are true HP 3500psi bottles and the only LP tanks I'd consider would be the PST104's, but since I like skinny 7.25" tanks over 8" tanks, there's not a lot of reason to buy the LP bottles for me. For most modern tanks though, I would definitely get the 3442 versions over the 2400 tanks any day.

 

[Peter69_56]

agreed, but so many years of this without a single incident and all of them passing hydro every 5 years means the pressure ratings were just too conservative, it was an industry standard and it is what it is. Like I said about, I own LP72's with a 2250 service pressure, fill to about 2800psi and that's it. The rest of my bottles are true HP 3500psi bottles and the only LP tanks I'd consider would be the PST104's, but since I like skinny 7.25" tanks over 8" tanks, there's not a lot of reason to buy the LP bottles for me. For most modern tanks though, I would definitely get the 3442 versions over the 2400 tanks any day.

Are new cylinders designed with overfill still or are we talking old cylinders only?

 

[scubastingray]

Are new cylinders designed with overfill still or are we talking old cylinders only?

They're nearly all over-engineered.

Seems you would take issue with my almost exclusively LP steel tank collection and my filling habits.

Aren't nearly identical tanks sold in other regulatory environments with higher fill pressures?

 

[muddiver]

Back to the OP's question:
If you boat dive a lot go Low Pressure because a lot of boats can't or don't do fills up to or over 3000psi.

If you always go to a dive shop for fills and most of the local dive shops where you frequent can and do fill up to 3000 psi or 3442 psi, go High Pressure. They have better buoyancy characteristics.

Easy pezzy

 

[scubastingray]

Back to the OP's question:
If you boat dive a lot go Low Pressure because a lot of boats can't or don't do fills up to or over 3000psi.

If you always go to a dive shop for fills and most of the local dive shops where you frequent can and do fill up to 3000 psi or 3442 psi, go High Pressure. They have better buoyancy characteristics.

Easy pezzy

That's a silly way to look at it, becuase you could get a similarly sized HP tank (that would be rated for nearly teh same amount of air at the equivalent LP). Then you are at least not limited when there are high pressure fills available. See the first post on this page.