Mixing gases in a cylinder for a partial fill

[rsingler]

I know when an entonox (laughing gas) cylinder sits in the cold it separates, not sure about the science.

Entonox is not 100% nitrous oxide. N2O becomes a liquid somewhere over about 700 psi (sorry - working from memory). So a full nitrous tank is actually liquid, and the gauge reads ~700 psi until all the liquid has vaporized and there is less than 700 psi of nitrous in the tank.
I would guess that the nitrous in Entonox (N2O and air at pressures over ~700 psi) would begin to return to a liquid phase over time, especially at low temperatures.

 

[m.taylor]

Cool, so N2O works like CO2. I learned something today.

 

[RainPilot]

Stupid question or not, I'll ask it here, because I don't know: Do gases separate in tanks after awhile?

No, but.... if you leave a tank long enough, you will lose helium from it as the molecules can escape the valve. The rate will depend on FHe and fill pressure and ambient temperature.

 

[rjack321]

No, but.... if you leave a tank long enough, you will lose helium from it as the molecules can escape the valve. The rate will depend on FHe and fill pressure and ambient temperature.

Helium does not preferentially "leak" past the valve seat or anywhere else for that matter.

The bailouts I filled with 9/72 three years ago are still full and still 9/72
The helium supply cylinder I bought 4 years ago is also still full

 

[RainPilot]

Helium does not preferentially "leak" past the valve seat or anywhere else for that matter.

The bailouts I filled with 9/72 three years ago are still full and still 9/72
The helium supply cylinder I bought 4 years ago is also still full

Huh. I was speaking from anecdotal discussions here on SB and with other trimix divers which I had assumed were correct. Now I have a different data point. I haven't personally held onto heavy trimix tanks for any real length of time.

 

[Norwegian Cave Diver]

If we were to take a tank of air and let it sit for a long time... does the heavier gas (oxygen vs nitrogen) settle in the tank? Requiring the tank to be remixed?
From a Google search...
Nitrogen gas has a molecular formula of N2 and a molecular weight of 28 g/mol. Thus, 1 mole of nitrogen gas weighs 28 g. Similarly, oxygen gas has a molecular formula of O2 and a molecular weightof 32 g/mol. ... This means that there is more oxygen than nitrogen in the same volume of gas.

 

[PfcAJ]

Helium does not preferentially "leak" past the valve seat or anywhere else for that matter.

The bailouts I filled with 9/72 three years ago are still full and still 9/72
The helium supply cylinder I bought 4 years ago is also still full

It definitely leaks out of Lola manifolds.

 

[michael-fisch]

Problems with those Czech Valves?

Michael

 

[PfcAJ]

Problems with those Czech Valves?

Michael

It’s the braided flexible crossbar.

many heliums were lost to bring us this information. #neverforget

 

[rddvet]

Yeah I was told to always close the isolator valves on the Lola. I'm not a big fan of having to do that sinde it's an easy thing to forget when you don't dive them often. But it is what it is