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Pressure Effect

swuest

Jul 1, 2013
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I have a question, but it isn't exactly about electronics. My project is a circuit that sends power to a gear motor which in turn, punctures a CO2 cartridge. But my application will be below sea level, and I was wondering if any CO2 could come out of a cartridge at depth like that?

CO2 is pressurized at 800psi in the cartridge
My application will be at 3000ft below sea level (1500psi)

I'm assuming no gas would come out if it was to be opened in that sort of pressure setting.

Thanks in advance for any help!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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I'm assuming no gas would come out if it was to be opened in that sort of pressure setting.

Yes, as soon as you puncture the seal, water will rush in.

With a large enough hole and the appropriate orientation you *might* get a bubble escaping after the pressures have equalised (when the container is about 1/2 full of water and the pressure of the now more highly compressed gas inside is around 1500psi).
 

swuest

Jul 1, 2013
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Thank you! That's what I was thinking. But someone was disagreeing with me, so I wanted to make double sure I was right. Although in my application, the CO2 cartridge will be attached to a buoy. Does that mean that the gas will be released since no water can actually get in? Or is the surrounding pressure still too great for any gas to escape?

Thanks!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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It would be trivial to test this.

Get a sealed container of air at atmospheric pressure. place the container at a depth of 1m and puncture the lid.

See what happens.

It probably won't be quite as dramatic as anything with 800psi behind it, but it will be similar once the pressure equalises.

The issue is likely to be one of surface tension across the puncture.
 

duke37

Jan 9, 2011
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With internal pressure of 800 psi and external pressure of 1500 psi, the likelyhood is that the container will buckle and the internal pressure will rise but there will be no avaiable gas to raise the buoy. CO2 is highly water soluble, hence fizzy pop.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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I charitably assumed that if the vessel can withstand a pressure differential of 785 psi, it could withstand a differential of 700 psi in the other direction.

I also considered the solubility, but even though it is quite soluble, I doubt it would be soluble in the volume of water that would enter the vessel.
 

duke37

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The fuel tanks on space rockets are only a few thou thick, they need internal pressure to keep them in shape, they will not stand any external pressure. An extreme example.

I had another thought, water is more or less incompressible but CO2 gas is not. Will the gas at 1700 psi have a density of more than that of water, if so, it will not produce any lift whatever.
 
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