Why would anyone dive HP tanks?

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Where are you guys buying manifolded double steels for $500? I've been looking at divesales.com, and they seem to have pretty good prices (better than my LDS at least), but I can't even get a set of doubled alu 80's with bands and isolation manifold shipped to my door for less than $500.


Thanks in advance!



David
 
Aren't my 104's HP? Renniker filles them to 4300. Peacock 1 to Olsen and back (peanut to crossover) and they are still full!

My wife uses double HP 100's because they are lighter on land. They still weigh as much as she does. I'm trying to get her to try LP 85's or 95's.
 
Originally posted by MikeFerrara
Aren't my 104's HP? Renniker filles them to 4300. Peacock 1 to Olsen and back (peanut to crossover) and they are still full!

You're way too well known to ask such a seemingly innocent question - :jester: - don't you own a dive shop or something?

PST 104's, for instance, are "low pressure" tanks and are rated to 2400 p.s.i. and may, with additional certification, be filled an additional 10%. According to DOT and TC, anyway. If you know of a 104cf tank rated to higher pressure, I'm interested.

I know the argument - DOT and TC are nincompoops (or morons from beyond the pale, if you prefer) that don't have a clue what they're doing and we should trust you and the DIR dark hordes when they tell us that it's okay to inflate an LP tank to whatever a compressor can squeeze out. I'm going to continue to play this one conservatively until someone can show the results of a solid scientific study demonstrating that an LP tank with a 2400+ rating can handle 4300 for an extended number of years.

Steven
 
Originally posted by reefraff
I'm going to continue to play this one conservatively until someone can show the results of a solid scientific study demonstrating that an LP tank with a 2400+ rating can handle 4300 for an extended number of years.


Is this proof enough? If you scroll down to the bottom of this link you will find the following information...

OMS Tank Specs

Hydro Test Pressure (psi) : 4000 psi
Minimum Burst pressure (psi): 6400 psi
Design Life: 10,000 Cycles at 4000 psi

I personally do not not anyone with 10,000 dives...


Dive often, dive safe

John
 
This is something I have been wondering about for some time. What is the real deal with HP/LP tanks? If you can safely fill a LP tank to 4300 psi (can you?) than why can't you fill a HP tank even more? What is the difference between a so called low pressure tank that gets a rating of 2400+ psi but is sometimes filled alot more and a so called high pressure tank that gets a rating of 3500 psi and it is never over filled.
I have been searching the board here for some information about the HP/LP debate and have found alot of good information but I am still not understanding the basics of it. If you have to tanks, both of the same liquid capacity (read that as "same size") and one is rated to 2400+ and one is rated to 3500 and the are both filled to 3500psi what makes the LP tanks better.
 
Originally posted by Cave Diver


Is this proof enough? If you scroll down to the bottom of this link you will find the following information...

OMS Tank Specs

Hydro Test Pressure (psi) : 4000 psi
Minimum Burst pressure (psi): 6400 psi
Design Life: 10,000 Cycles at 4000 psi

I personally do not not anyone with 10,000 dives...

Dive often, dive safe

John

Nope - this isn't even close to being proof.

This is a list of design specifications - for lack of a better phrase a maximum design tolerance. The inescapable fact remains that these tanks are certified by DOT and TC to a maximum of 2640 pounds, or 2400 pounds without the + rating. I don't see any science - independent lab or internal - to support any contention that their design ratings are real world numbers, so I have to assume that these numbers were developed by some earnest young engineer with a taste for metal alloys and are based upon extrapolations, not scientific rigorous testing. Indeed, OMS does NOT contend, recommend or even suggest that it's safe to pressurize these tanks to anything over 2640psi. In fact, the opposite is true - they issue a stern warning to the purchaser not to pressurize above the DOT/TC rating.

While we're on the subject of taking a dealer/manufacturers word at face value, OMS would really like for you to buy one of their Elastomeric Retraction Band BC's, which they categorically state are safe, effective and field proven. They even back up these claims with lab test results supplied by a purportedly independent third party. Argo Diving Service I'm under the impression that most cavers would rather stay dry than dive a BWOD rig, so if you're going to accept their statements as fact without need for verification, what's the basis for rejecting their statements regarding bungeed wings?

Dive often to dive safe!

Steven
 
Originally posted by omar
The only swing weight is from the weight of the gas used. If you use your HP100's down to 500 psi you will use more gas than AL80's and have more of a bouyancy change.

It is simple physics.

omar

Omar, I understand that. I should have said something to the effect of my HP100 is still negative when empty.
 
Originally posted by reefraff

The inescapable fact remains that these tanks are certified by DOT and TC to a maximum of 2640 pounds, or 2400 pounds without the + rating. I don't see any science - independent lab or internal - to support any contention that their design ratings are real world numbers, so I have to assume that these numbers were developed by some earnest young engineer with a taste for metal alloys and are based upon extrapolations, not scientific rigorous testing. Indeed, OMS does NOT contend, recommend or even suggest that it's safe to pressurize these tanks to anything over 2640psi. In fact, the opposite is true - they issue a stern warning to the purchaser not to pressurize above the DOT/TC rating.

Steven

Yes, and a bottle of childrens cough syrup has a stern warning that use of the product could cause drowsiness and that they shouldnt drive or operate heavy machinery while taking it. Not that I see many 5 year olds driving dump trucks anyway...

In today's litigious society there are many such warnings put there for the 'safety' of the public. The 10% overfill came into play during the war. Higher capacity was needed and the lack of available materials made the feasibility of retooling cylinders impractical. From DOT:
"In 1930, the ICC implemented regulations for periodic inspection and testing of cylinders; the regulations, as amended, were first published in the Federal Register on December 12, 1940 (5 FR 4908). During the 1930's and 1940's, the Compressed Gas Association (CGA) developed and refined the water jacket test method for determining the serviceability of a cylinder. During World War II, there was a shortage of high pressure gas cylinders. Because of CGA's work on steel wall stress limitations, the ICC granted "temporary'' regulatory relief to increase the gas carrying capacity of existing cylinders by allowing the cylinders to be filled 10% over their marked service pressures, and by marking those cylinders with a plus, "+'', mark. Ten years later, the regulations were codified into the Code of Federal Regulations (15 FR 8261; Dec. 2, 1950). In 1967, pursuant to the Department of Transportation Act, Pub. L. 89-670, 80 Stat. 931, regulatory responsibility for the transportation of dangerous articles in commerce was transferred from the ICC to DOT."

It was determined that they could easily go to 10% over rated capacity. I *believe* that this early capacity was set, not because of a weakness of design in the cylinders but rather due to a lack of widespread availability of compressors capable of achieving higher fill pressures. The DOT issuance is a U.S. regulation and it is my understanding that most European tanks are not even equipped with burst discs and it is a common practice for the tanks to be filled well beyond a 10% margin.

The premise is that steel tanks have a much higher tensile strength than aluminum tanks and because of that they stress more slowly from the cycle of being filled than does an aluminum tank. The problem that occurs with most steel tanks is that they will rust and become unusuable long before they will develop problems due to cracking, etc from being pressurized beyond the rated fill capacity.

The DOT states that a tank must pass hydrostatic testing equivalent to 5/3 of it's rated working pressure. For a 2400 psi tank with a 10% overfill (2640) that comes to a pressure of 4400 psi.

That does not mean that I would advocate filling a tank to 4000 psi on a regular basis. It simply means that a properly mantained tank that has not been subjected to any extraordinary stress (fire, etc) *should* be well capable of handling the 3500 psi cave fills that are commonly used.

I have read several good articles on this and if I can find find them again I will post a link or send them to you to see if it provides the facts you desire.

In regard to the BWOD, you are correct many cavers (as well as other divers) do not advocate their use. However I don't recall as those wings being marketed specifically at cavers and there seem to be some people who own and dive them safely that are quite happy with them (and no, I am not one of them). That however, is another topic for another post.

Dive often but dive safe

John
 
Originally posted by Burke
I have been searching the board here for some information about the HP/LP debate and have found alot of good information but I am still not understanding the basics of it. If you have to tanks, both of the same liquid capacity (read that as "same size") and one is rated to 2400+ and one is rated to 3500 and the are both filled to 3500psi what makes the LP tanks better.

One of the points that makes people advocate the use of LP cylinders it the fact that it places less stress on the compressor (depending on the setup of your LDS and whether they have adequate air bank) to pressurize a tank to 2600 psi vs 3500 psi. Also, the more psi you put in a tank, the more heat is generated and heat is a contributor to the stress of a tank, especially aluminum. Therefore many people see it favorable to use LP tanks vs HP tanks. However when the LP tanks are filled well past rated capacity (a common practice in some areas) that kind of nullifies the argument.

Hopefully this somewhat answered your question.

Dive often, dive safe

John
 

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