tank overfills HP vs LP
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JohnB47
Contributor
I really hope that nobody reading this gets confused by the quote from LeadKing about tensile strength. Tensile strength is NOT the same as the maximum air pressure the tank can hold, even though both are measured in psi. The tensile strength is the force required to permanently deform the steel divided by its cross-sectional area. Personally, I like the idea of buying an HP tank (rated at 3442 psi) and filling it to ~3000 psi. It will last longer that way. If I need more air, I can always buy a bigger tank or use doubles. As for the regulator rating, Scubapro lists it in the manual that comes with their regs. If I remember correctly, most of their recent ones are rated at ~4350 psi using a DIN connector, but the yokes are rated at 3362 psi (slightly less than the new HP tanks).
Peter_C
Contributor
So if my Worthington tanks are rated for 100,000 cycles and by overfilling them I lower that to 10,000 cycles per tank. With Six tanks that means I can only get 60,000 dives in before they are junk and my bones are swiss cheese
Are you recommending that I should make them last longer, since that might not be enough dives for me?
Dang it! I might have to try the duct tape and zip ties first 
adm3745
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I just thought of something that could be usefull for determining the strength of my individual tanks. I can throw some strain gauges on my tanks and take them to the lab and depressurize one from 2600 to maybe 100psi. Working backwards you think it would be reasonable for me to get acurate material properties? IF I were to discover the tensile strength of my tanks was on the upper end, I could maybe start filling to 2700??
Leadking
Contributor
Here is the data from my original posts (Feb 2007)
view all the posts at
[http://www.scubaboard.com/forums/tanks-valves-bands/177917-difference-between-lp-hp-tanks.html
Quote:
Originally Posted by Jimmer
The exemption question is a good one, maybe Lee from Sea Pearls can answer that for us, if he sees this thread.
As my name is mentioned, I will reply;
U.S.tensile strength (105,000-125,000 psi for 3AA cylinders) is not the same as European tensile strength (135,000-155,000 psi as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi for their 3AA cylinders (as required by DOT)
As an example, all of the E cylinders, Exempt or soon to be SP, Special Permit cylinders are made from a harder steel and cannot exceed 159,000 psi yield which exceeds 3AA tensile yield by as much as 50%. As you can see the E/SP cylinders being produced more closely follow the European metallurgy which allows for higher pressures.
and
Originally Posted by Arcaporale
Well I know that some European tanks are rated to 275 bar or 4000psi, but when the same tank is sold in North America it is rated to 2400+ because we have stricter laws. But then what makes a HP tank legal in the US? Is this some type of elaborate marketing scheme?
The only reasonable answer I can come up with is that LP tanks are designed to hold a certain volume at a lower pressure for people who don't have access to compressors the pump up to 3500, so they make a bigger tank and stamp a lower pressure on it and all of a sudden they got an LP tank.
A tank sold in the U.S. as a 2400+ cylinder which will be a DOT 3AA cylinder cannot have a tensile yeild greater than 125,000 psi and therefore would fall far short to qualify for a European HP cylinder. The confusion is that there are different steels used in construction. Manufacturers use the identical tooling to manufacure LP and HP cylinders, the difference is in the metallurgy not the dimensions of the cylinder.
I spoke with our engineers today and found that DOT 3AA cylinders have a typical tensile strength of 105,000-120,000 psi and Worthington's tensile strength on our X-Series (E-14157) is 135,000-155,000 psi with nominal at 145,000 psi which they tell me they hit "pretty well on the money" every time.
This demonstrates that a high pressure E cylinders is at least 30% higher tensile than 3AA cylinders.
Please pass this information on and do everything you can to stop the rumor that HP and LP cylinders are the same except for the markings.
and
Quote:
Originally Posted by Arcaporale
Well I know that some European tanks are rated to 275 bar or 4000psi, but when the same tank is sold in North America it is rated to 2400+ because we have stricter laws. But then what makes a HP tank legal in the US? Is this some type of elaborate marketing scheme?
The only reasonable answer I can come up with is that LP tanks are designed to hold a certain volume at a lower pressure for people who don't have access to compressors the pump up to 3500, so they make a bigger tank and stamp a lower pressure on it and all of a sudden they got an LP tank.
A tank sold in the U.S. as a 2400+ cylinder which will be a DOT 3AA cylinder cannot have a tensile yeild greater than 125,000 psi and therefore would fall far short to qualify for a European HP cylinder. The confusion is that there are different steels used in construction. Manufacturers use the identical tooling to manufacure LP and HP cylinders, the difference is in the metallurgy not the dimensions of the cylinder.
view all the posts at
[http://www.scubaboard.com/forums/tanks-valves-bands/177917-difference-between-lp-hp-tanks.html
Quote:
Originally Posted by Jimmer
The exemption question is a good one, maybe Lee from Sea Pearls can answer that for us, if he sees this thread.
As my name is mentioned, I will reply;
U.S.tensile strength (105,000-125,000 psi for 3AA cylinders) is not the same as European tensile strength (135,000-155,000 psi as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi for their 3AA cylinders (as required by DOT)
As an example, all of the E cylinders, Exempt or soon to be SP, Special Permit cylinders are made from a harder steel and cannot exceed 159,000 psi yield which exceeds 3AA tensile yield by as much as 50%. As you can see the E/SP cylinders being produced more closely follow the European metallurgy which allows for higher pressures.
and
Originally Posted by Arcaporale
Well I know that some European tanks are rated to 275 bar or 4000psi, but when the same tank is sold in North America it is rated to 2400+ because we have stricter laws. But then what makes a HP tank legal in the US? Is this some type of elaborate marketing scheme?
The only reasonable answer I can come up with is that LP tanks are designed to hold a certain volume at a lower pressure for people who don't have access to compressors the pump up to 3500, so they make a bigger tank and stamp a lower pressure on it and all of a sudden they got an LP tank.
A tank sold in the U.S. as a 2400+ cylinder which will be a DOT 3AA cylinder cannot have a tensile yeild greater than 125,000 psi and therefore would fall far short to qualify for a European HP cylinder. The confusion is that there are different steels used in construction. Manufacturers use the identical tooling to manufacure LP and HP cylinders, the difference is in the metallurgy not the dimensions of the cylinder.
I spoke with our engineers today and found that DOT 3AA cylinders have a typical tensile strength of 105,000-120,000 psi and Worthington's tensile strength on our X-Series (E-14157) is 135,000-155,000 psi with nominal at 145,000 psi which they tell me they hit "pretty well on the money" every time.
This demonstrates that a high pressure E cylinders is at least 30% higher tensile than 3AA cylinders.
Please pass this information on and do everything you can to stop the rumor that HP and LP cylinders are the same except for the markings.
and
Quote:
Originally Posted by Arcaporale
Well I know that some European tanks are rated to 275 bar or 4000psi, but when the same tank is sold in North America it is rated to 2400+ because we have stricter laws. But then what makes a HP tank legal in the US? Is this some type of elaborate marketing scheme?
The only reasonable answer I can come up with is that LP tanks are designed to hold a certain volume at a lower pressure for people who don't have access to compressors the pump up to 3500, so they make a bigger tank and stamp a lower pressure on it and all of a sudden they got an LP tank.
A tank sold in the U.S. as a 2400+ cylinder which will be a DOT 3AA cylinder cannot have a tensile yeild greater than 125,000 psi and therefore would fall far short to qualify for a European HP cylinder. The confusion is that there are different steels used in construction. Manufacturers use the identical tooling to manufacure LP and HP cylinders, the difference is in the metallurgy not the dimensions of the cylinder.
Last edited:
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