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?

 

[Angelo Farina]

Please don’t just throw out fatigue or stress/strain…I want numbers and/ or credentials.

I have a very hard time believing a 6% overfill exceeds any safety factor.

Edit: I’m not advocating for cave filling aluminum , just that a +200psi mistake is not the end of the world.

The safety factor for any tank, wathever the material, is mandated to be 50%.
When the tank are hydroed, if they are stamped for 200 bar, they fill them (with pressurised water) at 300 bar.
So a 6% overfill is substantially irrelevant.
However during hydro you sometimes see alu tanks to literally break apart, while steel tanks are condemned just for dilating more than the allowed tolerance.
So at the structural crisis point alu and steel behave differently. Steel plasticizes, but does not explode suddenly. Alu instead is much more dangerous.
That's the reason for which steel tanks are considered more "safe" for overfilling.
But luckily there is not a statistically relevant number of cases of explosion of alu tanks, as no one is so stupid to fill them at 300+ bars.
So there are no numbers regarding accidents. There are numbers regarding failed hydro tests.

 

[Eric Sedletzky]

Are they

PSTs?

They are tanks from 1967 through 1980.
Probably?
I would have to look.

 

[Bearded Diver]

Careful: Aluminum cylinders are different than steel. If your Al 80 is filled so that it is 3,150/3,200 psig warm, but cools to 3,000, then this is probably okay. It's better (perhaps) for an Al 80 to be filled to 3,000, then allowed to cool, and then topped-up to 3,000.

rx7diver

After it’s cooled it lands about 3050/3100, but the 3100 was only once.

 

[Bearded Diver]

Do you have any data on this? Sounds like keyboard engineering to me.

Please don’t just throw out fatigue or stress/strain…I want numbers and/ or credentials.

I have a very hard time believing a 6% overfill exceeds any safety factor.

Edit: I’m not advocating for cave filling aluminum , just that a +200psi mistake is not the end of the world.

The shop owner sometimes overfills all tanks, not what I’d recommend anyone do, but then again an extra 50 psi 3050 is the typical full, those higher numbers were few and far between, isn’t bad imo

 

[Bearded Diver]

They are tanks from 1967 through 1980.
Probably?
I would have to look.

If you ever glance at them, love to know what the make is?