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?

 

[lexvil]

I think I’ll get a Sharpie and write “please overfill” on it, sharpies are very powerful tools.

 

[Eric Sedletzky]

If it makes any difference to you, I work with people whose whole job is the failure and fracture of metals. They assure me that there is effectively no danger in filling a steel tank to a pressure that the tank has seen before. Steel is quite flexible and the grain structure stretches like a rubber band. It won't break unless you take it past the breaking point. I don't blame any shop or person for not wanting to take on the risk of an overfill, but it's exceeding unlikely, closer to a lightning strike type of event.

Once the tank has been filled, it starts to cool and shrink, relieving the stress. As long as you keep the tank cool it will be fine. I'm not sure there has ever been an instance of a tank exploding on a user's back. The risk is borne by the fill station, not you.

I would think it would actually be safer to have the tank fairly hot when it’s overfilled, it makes the steel more elastic. I would also think that it would be worse to have an excessively overfilled tank that is freezing cold. I would think the steel would technically be more brittle.

 

[Eric Sedletzky]

Yes, but the issue is worrisome only for many 1000's or 10's of thousands of cycles, not the few our cylinders undergo, and even then it is for stressing to near maximum, towards the elastic limit, not the lower levels we use in scuba.

Somebody would have to take it to the max every time it’s filled for years. I’m not so sure it would make the tank that much more prone to exploding though. It would just eventually lose elasticity and fail a hydro. That may not mean that when it’s at it’s max it’s any more liable to suddenly give way, it’s just not retracting back to where it should be. Whether or not it makes the tank more brittle within it’s maximum pressure value, IDK?

 

[rob.mwpropane]

I would think it would actually be safer to have the tank fairly hot when it’s overfilled, it makes the steel more elastic. I would also think that it would be worse to have an excessively overfilled tank that is freezing cold. I would think the steel would technically be more brittle.

That's an interesting thought, but I believe the temp of the steel isn't really a factor like we would assume. Let's say you get a hot fill and the tank is 140°... is that really all that hot to steel? It could get up to the same temp sitting in a hot car. Just because it's "hot" to us doesn't mean it's hot.

I would think you're right just on a much smaller scale, like one that really probably doesn't matter (to steel).

I am not an engineer, but I have worked with a lot of "cold" and "hot" steel... I've never seen it do anything different at ambient temps. I could be totally wrong... I never claim to be right, that's just my thought process. I know you work with metal, what do you think?

 

[rongoodman]

I think I’ll get a Sharpie and write “please overfill” on it, sharpies are very powerful tools.

They can, after all, divert hurricanes.

 

[Eric Sedletzky]

That's an interesting thought, but I believe the temp of the steel isn't really a factor like we would assume. Let's say you get a hot fill and the tank is 140°... is that really all that hot to steel? It could get up to the same temp sitting in a hot car. Just because it's "hot" to us doesn't mean it's hot.

I would think you're right just on a much smaller scale, like one that really probably doesn't matter (to steel).

I am not an engineer, but I have worked with a lot of "cold" and "hot" steel... I've never seen it do anything different at ambient temps. I could be totally wrong... I never claim to be right, that's just my thought process. I know you work with metal, what do you think?

I think it’s probably true on a micro scale, and since we’re here intellectualizing about it what the hell? More for the conversation.

 

[SubseaSports]

OP, never get a fill in north central Florida...........you'll have a panic attack.

Even my propane tanks get overfilled up here .

Having said that, I rarely put my lp85s past 3200. I even do self serve at my lds.

 

[Divin'Papaw]

I have an X7-100 Worthington that I bought in 2007. It just passed its 4th hydro counting the original hydro at manufacture. It has been overfilled to 3600-4200 regularly. The key thing is though, being a personal tank, there is just no way it sees enough fill cycles to make a hill of beans worth of different. It is used and then filled (overfilled) at most twice a month. Given how well I take care of my tanks, it will very likely still be passing hydros when I am no longer fit to dive.

 

[Eric Sedletzky]

That's an interesting thought, but I believe the temp of the steel isn't really a factor like we would assume. Let's say you get a hot fill and the tank is 140°... is that really all that hot to steel? It could get up to the same temp sitting in a hot car. Just because it's "hot" to us doesn't mean it's hot.

I would think you're right just on a much smaller scale, like one that really probably doesn't matter (to steel).

I am not an engineer, but I have worked with a lot of "cold" and "hot" steel... I've never seen it do anything different at ambient temps. I could be totally wrong... I never claim to be right, that's just my thought process. I know you work with metal, what do you think?

140 to steel is nothing.
Steel begins to turn brown at 480 degrees, it begins to tirn blue at 520 degrees.
The first brown coloration is technically when it’s soft enough to move with some persuasion.
In my auto body days when we needed to shrink steel where a dent was we would work out the dent first then strip all the paint off the outside. If the metal was stretched from being hit which is always common, then we would begin to heat the steel with a torch on the outside just to the point that it began to turn brown and the metal would raise up. Immediately following the heating we would bump the high spot in with a body hammer working the metal back in shape. What that does is gathers the steel back up and compresses the grain back to shape. When it cooled we would check it and if needed we would repeat the process.
Scuba tanks are obviously a much stronger alloy than car bodies but I don’t know the mix. I know tanks are not just mild steel.

 

[Rose Robinson]

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?

Hi Ted,

I'm sure by now you've had a look at most of the responses, and as you can clearly see, the opinions are varied.

Being one who has made it a life practice to adhere to manufacturers instructions, I'd be inclined to follow the information stamped onto your cylinders.

No certified fill station attendant was ever instructed by a certified instructor that it is acceptable to over-pressurize scuba cylinders.

Filling a scuba cylinder to stamped operating pressure is not difficult.

If the fill station attendant cannot get it right, what else does he/she do wrong. If this same person is also reg service certified, I do not think I'd have them servicing my regs.

What ever happened to plan the dive, and dive the plan?

Sorry folks, just me, carry on as you see fit.

LOL

Rose