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How does moisture enter a tank?

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Naked Diver

New Member
Jun 19, 2021
Apparently a tank without much air pressure in it can get moisture entering. How is this possible if the tank is air tight? Surly it's therefore also water tight?


Active Member
Sep 5, 2019
That may not be an inherent or common issue, moisture in the tank is most likely due to compressor not getting all water separated from air or condensation during rapid pressure loss. If the tank goes empty during use, there is nothing preventing it from scavenging water from the regulator or other sources when valve is open especially if under water. Various reasons to keep pressure in the tank, it may reduce fatigue due to the cylinder not shrinking to its minimum diameter. If the tank is fully evacuated the seal may allow water in if there ends up being a vacuum pressure differential and valve is not tight. The valve seat with Teflon face may seal better under pressure. Pressure gauges do not read low pressures in order to ensure tank is not fully evacuated.
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