Let’s say you have a tank that’s 4350 psi and the dive shop fills it, how much psi can you expect to lose during cool down? Also can’t you fill it beyond the rating to compensate for the subsequent cool down?
Tank cool off and loss of psi
- Thread starter Haganaga
- Start date
I drop off my tanks to my local dive shop, then come back in a couple hours.
They fill, then after a while, they top the tanks off.
They get them at or close to 4500 that way.
They fill, then after a while, they top the tanks off.
They get them at or close to 4500 that way.
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going from 4350 to 4500 I wouldn't think you should get any loss, but from 3000 to 4500 yes, the person that fills mine leaves it hooked up and fills let it cool and does this over a few hours, and when I show up to get it he tops it off one last time. and he said he will not over fill a carbon fiber tank for cooling loss but would a steel tank.
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The safest bet is to do what the guys mentioned above.
However, at the FD we usually fill to ~4650 to end up at ~4500. We're working off a cascade system and do not have the time to fill slow enough to not se pressure loss. That being said, we're surely not "flash" filling and if a bottle comes out too hot, someone will get a talking to!
Tom
However, at the FD we usually fill to ~4650 to end up at ~4500. We're working off a cascade system and do not have the time to fill slow enough to not se pressure loss. That being said, we're surely not "flash" filling and if a bottle comes out too hot, someone will get a talking to!
Tom
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Over pressurizing a tank is one of those things we don't talk about or tell people to do...wink wink, It happens all the time though. When a tank is hydro tested, it is filled and over pressurized with an uncompressible liquid, water, to 5/3 of the tanks working pressure. 5/3 of 3000psi is about 5000psi. 5/3 of 4150psi is about 6916psi. These pressures are obviously way higher than the 150-200psi people might over fill their tanks to get maximum fill pressure. That's a huge safety margin. With that being said... a catastrophic tank failure is not something you want to be anywhere near!
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You will probably notice that the metric rating of 300 bar is less than the 4500 psi on some bottles. They're all the same. It is just less confusing to use round numbers. As has already been covered, there is a very wide safety margin between the working pressure and the burst pressure. If you filled your bottle in winter and left it sit around until summer, you will likely get a rise of a couple of hundred psi.
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