Short Fills In HP Tanks

[H2O 70]

Just remember that it is roughly 7psi per degree. If the shop filled them put 3400 at 115degrees and they are then stored in 70degree air, or sit on a concrete floor that is even cooler, you're talking 40degrees or 280psi. 115 doesn't feel that warm. That is only 20 degrees warmer than us.

I would bet you the tech shop is anticipating the drop and overfilling. Burst disks are rated at 140% of rated pressure. They may fill up to 3600-3700psi anticipating the cool down and that is well within the rated pressure of the burst disk.

 

[Scott L]

Just remember that it is roughly 7psi per degree. If the shop filled them put 3400 at 115degrees and they are then stored in 70degree air, or sit on a concrete floor that is even cooler, you're talking 40degrees or 280psi. 115 doesn't feel that warm. That is only 20 degrees warmer than us.

I would bet you the tech shop is anticipating the drop and overfilling. Burst disks are rated at 140% of rated pressure. They may fill up to 3600-3700psi anticipating the cool down and that is well within the rated pressure of the burst disk.

I question that. Otherwise I would hear a giant hissing sound coming from cave country to my north...

 

[fppf]

You can measure and feel how hot the cylinder is all you want.
Fact is, still air is an insulator, and a pretty good one at that. I have done a lot of experiments and made very accurate pressure measurements with calibrated pressure transducers. The internal gas temperature I calculated after a standard fill from a local shop was about 140 degrees. While the surface of the steel cylinder stayed about 115 degrees, warm to the touch but you could keep your hand on it. It took about 4-6 hours for the cylinders pressure to stabilize out in still room air of 70 degrees.

People freak out and argue about water baths during fills. They also say how it only effects a few PSI. But in fact, most industrial gas suppliers will use water misting the cylinders during filling to keep them cool. Especially when filling oxygen at acetylene. Putting a high speed fan like they use to dry floors on a cylinder while filling will also keep the internal temperatures down. Its much easier to keep the temperatures down while filling then to fill it and try to cool it down after the fact.

 

[fppf]

I question that. Otherwise I would hear a giant hissing sound coming from cave country to my north...

Actually, burst disks are rated for the hydro test pressure most times. 5000 PSI for an AL80, 5250 for a HP steel.

Cave country likes to work outside the law, they often plug or put burst disks in that are to high of pressure for that cylinder.

 

[H2O 70]

I question that. Otherwise I would hear a giant hissing sound coming from cave country to my north...

My HP100 and HP130's have rated pressures of 3442 and have burst disks rated to 5250, which is actually about 140%. I have a book here called the Encyclopedia of Recreational Diving where on 3-51 it states that burst disks are typically 140% of rated pressure.

What are you questioning?

 

[H2O 70]

Cave country likes to work outside the law, they often plug or put burst disks in that are to high of pressure for that cylinder.

I've heard them say they've never heard of a diver dying because a valve or tank ruptured, but they have heard of people dying because a disk let go.

 

[merxlin]

Regarding boat fills- most (not all) of the boats out here in So Cal fill to 3000psi max. So LP tanks get full fills but HP's typically do not. However, an HP100 is about the same size as an LP-85 and at 3000 psi has about the same capacity as the + rated LP. What that means for us is that you bring on a full HP100 for your first dive (usually deepest) then get 87-88cf on subsequest dives with boat fills.

 

[fppf]

I've heard them say they've never heard of a diver dying because a valve or tank ruptured, but they have heard of people dying because a disk let go.

Something that everyone says but has zero documented cases. And that is what an isolation manifold is for. And if you don't overfill your cylinders its not really and issue. And it is recommended to change the disk at least every hydro, something that everyone over looks as well.

There have been documented cases of cylinder failures, that is why they invented the burst disk. Then the first types where lead plugs, and there where cases of the plug turning into a bullet. Then they came out with the copper disk type, and pieces of the copper turned into shrapnel and injured someone. Which now we have the captured copper disk. Took a lot of issues to make it this far, lets not throw all the lessons away.

And lets get back on track and not get into the cave subculture argument, yet again.

As a side note, I drove wreckers for many years, I have seen seat belts be the primary cause of someones death. But 99.99% of the time they save lives and reduce injury.

 

[halocline]

The weird thing is, I have watched them fill my tanks, and felt how warm they get. I didn't have a thermometer with me, but it was reasonable. I think they may have the pressure gauge on their fill station intentionally set short, or something, because I have picked up a tank, had them top it off, and still seen it hundreds of PSI lower later on.

I think the air inside is a lot hotter than the surface of the tank. If you had a thermometer that would stick on the outside of the tank, I bet you could see the temp continue to rise for several minutes after the fill; that would indicate the air is hotter.

I've gone through this with my LDS many times. Usually I bring the tanks back the next day and they gladly top them off. That doesn't work if you're going diving right away, though!

 

[Scott L]

My HP100 and HP130's have rated pressures of 3442 and have burst disks rated to 5250, which is actually about 140%. I have a book here called the Encyclopedia of Recreational Diving where on 3-51 it states that burst disks are typically 140% of rated pressure.

What are you questioning?

It sounded low to me so I was opening up a discussion not questioning anything else. Sounds like you have the facts. Thanks!