It says right on my tanks - DO NOT OVERPRESSURIZE

[Ted Judah]

A year ago, I bought tanks for my wife and I. In that year we have used them on 16 dives and had them filled at 5 different dive shops. The pressures after each fill seem to vary wildly and is often overfilled.

Here are the markings on the tanks:

FABER MADE IN ITALY M8303 21/0154/ 073 02•21+
TC - 3AAM - 184/DOT - 3AA2400 DO NOT OVERPRESSURIZE REE67 BS85S


Below are the start fill pressures for each dive:

2400 lbs.
3400 lbs.
2600 lbs.
2500 lbs.
2500 lbs.
2500 lbs.
2200 lbs.
2800 lbs.
2800 lbs.
2800 lbs.
2950 lbs.
2400 lbs.
3000 lbs.
2750 lbs.
3250 lbs.
3525 lbs.

Am I missing something? should I be concerned? Should I request a certain pressure from dive shops?

 

[Manatee Diver]

A diver who is conservative enough to preserve the excess gas as a safety margin is likely also the dive to instruct shop not to do overfill.

You would be wrong. Proper gas reserves are probably most respected (though still broken) in the cave community, yet the cave community is also most known for overfilling that it is commonly known as a cave fill.

 

[NDonahue]

You would be wrong. Proper gas reserves are probably most respected (though still broken) in the cave community, yet the cave community is also most known for overfilling that it is commonly known as a cave fill.

I think you missed my point. Assuming all gas planning could be reduced to the rule of thirds, a diver with an overfilled tank is still going to use a third for outbound and a third for return. Having an overfilled tank doesn’t offer any additional margin of safely to the diver unless they reserve a higher percentage. All it does is allow a deeper cave penetration without any additional conservatism.

 

[Manatee Diver]

I think you missed my point. Assuming all gas planning could be reduced to the rule of thirds, a diver with an overfilled tank is still going to use a third for outbound and a third for return. Having an overfilled tank doesn’t offer any additional margin of safely to the diver unless they reserve a higher percentage. All it does is allow a deeper cave penetration without any additional conservatism.

Except I wasn't replying to that, but the statement that people who believe in having proper reserves are also the same people that don't do overfills. When in reality it is the opposite.

And it isn't hypocrisy but comes from experience in the area. If cave fills were unsafe then the shops wouldn't be doing them as it would be a danger to themselves and their employees (as the fill stations and operators take the highest risk). But yet hundreds of cave fills are done everyday.

 

[inquis]

Assuming all gas planning could be reduced to the rule of thirds

This is where you went wrong.

 

[Outbound]

I think you missed my point. Assuming all gas planning could be reduced to the rule of thirds, a diver with an overfilled tank is still going to use a third for outbound and a third for return. Having an overfilled tank doesn’t offer any additional margin of safely to the diver unless they reserve a higher percentage. All it does is allow a deeper cave penetration without any additional conservatism.

I'm not sure I follow. Yeah, that first third is being used on the way there, and the second third on the way back. But that last third is for reserve, and if you have a larger starting volume of gas you then have a larger remaining third for reserve. Now, I'm not going to argue that the way to add conservatism to a dive is to overfill tanks, but more gas in reserve is more gas in reserve.

 

[NDonahue]

Except I wasn't replying to that, but the statement that people who believe in having proper reserves are also the same people that don't do overfills. When in reality it is the opposite.

cool. I guess I pulled us down the rabbit hole.

I didn’t intend to imply that people who cave fill don’t follow safe gas planning. I was originally responding to someone who implied that “more gas is safer” as a justification for cave fills. In that original context I was trying to say that the extra gas in cave fills isn’t typically used to increase the margin of safety, but rather the increased gas is used (within the same safe gas planning processes that almost all divers follow) to extend the dive.

I jumped into this convo because I’m interested in how it became the norm to overfill in cave country. You all are lucky that some early divers and shops were willing to push the boundaries, and that enough positive experiences have shown that it’s safe to overfill such that it’s now common practice in North Florida.

Personally I’m more of a deep wreck diver so I lived first hand through the time of Pyle stops when a few influential divers with not much data convinced us to do deep stops. Most divers now agree (based on actual data) that deep stops were a bad idea. That experience taught me to be wary of deviation from standards. Who knows, maybe I’m too conservative.

One of the things I love about diving is the tension that exists between following the rules and processes that keep a diver safe while sometimes simultaneously bending some of the rules to push boundaries and extend the sport.

 

[Manatee Diver]

I didn’t intend to imply that people who cave fill don’t follow safe gas planning. I was originally responding to someone who implied that “more gas is safer” as a justification for cave fills. In that original context I was trying to say that the extra gas in cave fills isn’t typically used to increase the margin of safety, but rather the increased gas is used (within the same safe gas planning processes that almost all divers follow) to extend the dive.

There is an argument that super high pressure cave fills provide better margin of safety.

So lets say you get a 4,200psi fill. That gives you a 1,400psi third for penetration. But that means that third is is from 2,800psi to 4,200psi the pressure at which Z factor means you get less actual gas for the given pressure. So that means you go through it more quickly as you still need the same amount of gas to get IP.

Now this is one of stupid post dive arguments you have while waiting for dinner because we are probably talking maybe a few percent difference. And 4,200psi cold is very very hard to get.

 

[Superlyte27]

cool. I guess I pulled us down the rabbit hole.

I didn’t intend to imply that people who cave fill don’t follow safe gas planning. I was originally responding to someone who implied that “more gas is safer” as a justification for cave fills. In that original context I was trying to say that the extra gas in cave fills isn’t typically used to increase the margin of safety, but rather the increased gas is used (within the same safe gas planning processes that almost all divers follow) to extend the dive.

I jumped into this convo because I’m interested in how it became the norm to overfill in cave country. You all are lucky that some early divers and shops were willing to push the boundaries, and that enough positive experiences have shown that it’s safe to overfill such that it’s now common practice in North Florida.

Personally I’m more of a deep wreck diver so I lived first hand through the time of Pyle stops when a few influential divers with not much data convinced us to do deep stops. Most divers now agree (based on actual data) that deep stops were a bad idea. That experience taught me to be wary of deviation from standards. Who knows, maybe I’m too conservative.

One of the things I love about diving is the tension that exists between following the rules and processes that keep a diver safe while sometimes simultaneously bending some of the rules to push boundaries and extend the sport.

You forget that it wasn’t us that just started cave filling one day. A tank manufacturer literally wrote in their marketing material to say, “Guaranteed 10,000 fills at 4000 psi”

 

[Eric Sedletzky]

I think you missed my point. Assuming all gas planning could be reduced to the rule of thirds, a diver with an overfilled tank is still going to use a third for outbound and a third for return. Having an overfilled tank doesn’t offer any additional margin of safely to the diver unless they reserve a higher percentage. All it does is allow a deeper cave penetration without any additional conservatism.

I know what you’re saying, more gas pumped into a LP tank over it’s rated pressure more than likely means that the extra gas becomes part of the dive plan, not an extra reserve portion. In that case to be “proper” just get a bigger tank. They do, and then they overfill those too and that new extra amount of gas becomes part of the regular dive plan, and so on.

 

[Bearded Diver]

My 72 is stamped "USD" and "U.S. Divers" (the old name of Aqua Lung; google says the name change happened in 2003). I am almost certain (99.9% certain) that it was manufactured by Pressed Steel Tank Company (PST).

My university open water scuba course (NAUI/YMCA, in 1986) used these cylinders in class--except, some of those were already very old at that time. They were/are owned by the university. Last year, my daughter took the same course, which continues to use these very same cylinders!

rx7diver

Very cool. Thank you for the information. I appreciate it.
I started learning more about steel tanks when I was looking to buy my first set, read on SB that Simone was diving 50 year old tanks and they were steel. Flash forward to Thanksgiving day ‘21 and I bought two Faber HP 133’s. At $400 for both it was a great deal imo. I look forward to acquiring old tanks made well before I was around sicne they not only look cool, some are reasonably priced and are overfilled by the cavers all the time. Happy diving.