Oh no! My 72s are too small for tech classes! :(

[p_kos]

What is Z factor? That’s the first time I have heard that term.

Does anybody know what the failure pressure of a LP tank is? Has anybody ever exploded one to test?

Not sure what the failure pressure is but it’s much higher than 4000 psi which is the hydro test pressure for LP tanks. Z factor is gas compressibility factor.

 

[Jack Hammer]

Hmmm:

1. Old-school steel 72 nominally gives 71.2 cu ft @ 2,475 psig. I understand that these are routinely (albeit unwittingly) filled to 3,000 psig, so, 86.3 cu ft.

2. Al 80 nomially gives 77.4 cu ft @ 3,000 psig. "Never" overfilled (since Al).

3. LP 85 nominally gives 81.1 cu ft at 2,640 psig. I understand that these are routinely (perhaps unwittingly) filled to 3,000 psig, so, 92.2 cu ft.




[My emphasis.] Now, this makes perfect sense (to me)!

rx7diver

All the steel 72s I own are 2250psi tanks with a plus rating. So 72cf @2475psi. One can't depend on lp72s being overfilled or even filled to their plus rating as some shops just won't for whatever reasons. Therefore a 72 may only be able to supply 65cf. Point is the instructor may feel double 65s are not guaranteed to supply an adequate volume for the multiple ascents/descents, air shares, etc during the course.

 

[tbone1004]

What is Z factor? That’s the first time I have heard that term.

Does anybody know what the failure pressure of a LP tank is? Has anybody ever exploded one to test?

Compressibility factor - Wikipedia

en.wikipedia.org

Z Factors for SCUBA | Dive Gear Express®

Z Factors for SCUBA Cylinder volume is defined by the internal dimensions of the tank, and normally measured in cubic inches or liters of water. Free capacity is ...

www.divegearexpress.com

3aa cylinders should be good for no less than 10,000 cycles *it may be 12,000 I can't remember* to test pressure with a burst pressure somewhere around 2x test pressure or just over 3x working pressure. I can't remember what the actual standard is, but burst is somewhere around 7500psi. Some cylinders from the manufacturing lot has to pass either 10,000 cycles to test pressure or 100,000 cycles to working pressure. Since 100,000 cycles takes a lot more time to test than 10,000, the manufacturers usually do test pressure cycling. After that cycle test, the cylinder MUST pass a hydrostatic test.
10,000 cycles is a LOT of filling, basically 15 years of 2x/day filling to 4,000psi on a LP tank. There are LP104's in cave country that are much older than 15 years and have done a lot more than 10,000 cycles and are still passing hydro

 

[jtsfour]

Compressibility factor - Wikipedia

en.wikipedia.org

Z Factors for SCUBA | Dive Gear Express®

Z Factors for SCUBA Cylinder volume is defined by the internal dimensions of the tank, and normally measured in cubic inches or liters of water. Free capacity is ...

www.divegearexpress.com

3aa cylinders should be good for no less than 10,000 cycles *it may be 12,000 I can't remember* to test pressure with a burst pressure somewhere around 2x test pressure or just over 3x working pressure. I can't remember what the actual standard is, but burst is somewhere around 7500psi. Some cylinders from the manufacturing lot has to pass either 10,000 cycles to test pressure or 100,000 cycles to working pressure. Since 100,000 cycles takes a lot more time to test than 10,000, the manufacturers usually do test pressure cycling. After that cycle test, the cylinder MUST pass a hydrostatic test.
10,000 cycles is a LOT of filling, basically 15 years of 2x/day filling to 4,000psi on a LP tank. There are LP104's in cave country that are much older than 15 years and have done a lot more than 10,000 cycles and are still passing hydro

Oh... I always assumed test pressure was closer to failure than that. Well now I need someone with a slow motion camera to overfill one to bursting for my entertainment.

What about HP steel? Are they built as conservatively as the low pressure ones? Would that mean a HP Steel would fail at around 10,500 PSI?

 

[tbone1004]

Oh... I always assumed test pressure was closer to failure than that. Well now I need someone with a slow motion camera to overfill one to bursting for my entertainment.

What about HP steel? Are they built as conservatively as the low pressure ones? Would that mean a HP Steel would fail at around 10,500 PSI?

test pressure is nowhere near burst, the burst discs are supposed to be around 90% of test pressure, which is about what we cave fill the LP steels to for reference.
I believe the HP steel burst pressure is still around 3x working pressure. They are tested to 3/2 instead of 5/3 working pressure so the burst is probably in a similar 8000psi ish range.

 

[Wibble]

Burst discs... Never seen one. Are they common in the US?

 

[Marie13]

Burst discs... Never seen one. Are they common in the US?

On all our tanks.

 

[Wibble]

What happens when they burst? Aside from a bang and disc shrapnel thrown across the room! Can you just push the disc back in?

Seriously, have never seen one!

 

[Marie13]

What happens when they burst? Aside from a bang and disc shrapnel thrown across the room! Can you just push the disc back in?

Seriously, have never seen one!

The guys can address that.

 

[rob.mwpropane]

What happens when they burst? Aside from a bang and disc shrapnel thrown across the room! Can you just push the disc back in?

Seriously, have never seen one!

Well for starters I think it's mandatory to poop your pants.