probably a stupid ?

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OBXDIVEGUY

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I'm changing out my valves on my tanks and was just curious, what is the purpose of the little dip tubey thing that comes off the valve into the tank.?
 
oh, that makes sense. thanx
 
Actually, it is more than that. In the era of steel tanks, it also kept any corrosion from blocking the valve. There could be some small flakes of corrosion that could otherwise get into the tank's valve, and block air from going through the valve.

Concerning the water in the tank, it is also more than corroding your regulator. It has to do with the fact that a tank left drained, with the regulator intact and the purge pressed, can gain water if it goes deeper. There was a case of a diver in the tropics (it's somewhere on the ScubaBoard threads) who dove a rental tank, not knowing that it had several quarts of salt water inside. When he went inverted, that water was pushed by the tank pressure through the valve, his regulator and into his mouth--UUGGHH! But it takes significantly more water to do this with this tube on the valve. It won't happen with, say a cup full, in the tank.

SeaRat
 
Not just water, but even more important is preventing any kind of particles or dust (from rust, aluminum oxide, etc.) from entering and clogging the valve or filter when you are head down.

The best tubes are closed at the end with two or four holes on the side near the end. This would prevent the rare possibility of a particle falling from the bottom of the tank and going right into the end of the tube and clogging it.
 
https://www.shearwater.com/products/perdix-ai/

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