How does moisture enter tanks?

[Tracy]

I can throw a disconnected gauge in the pressure pot and run it to depth if that would make you happy. It will read the same pressure as the pot. It is gauge pressure.

 

[Subcooled]

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?

If the valve is closed tight then no water vapour can enter. Period.
There is however, some moisture in the gas inside.
If there is a temperature drop, then that moisture could condensate into water.

Do not fll your cylinders with warm moist air and then store them in the cold!

 

[Bert van den Berg]

If your LDS does a hydro on your tank and doesn't do a good job if drying the tank some residual water could stay in the tank.

 

[lowwall]

I can throw a disconnected gauge in the pressure pot and run it to depth if that would make you happy. It will read the same pressure as the pot. It is gauge pressure.

Please do. I now suspect you are correct and I was fooled by statements like "Gauge pressure is zero-referenced against ambient air" that are all over the web. But it would be nice to know for sure.


Thanks.

 

[Tracy]

Please do. I now suspect you are correct and I was fooled by statements like "Gauge pressure is zero-referenced against ambient air" that are all over the web. But it would be nice to know for sure.


Thanks.

Video 1 of the different gauges and expected outcome.


Video 2 of the same gauges at depth.


For those not wanting to waste two minutes of their lives watching poorly made videos, they did exactly what they should have. The two gauges that were intact read the pressure at depth, the two gauges equalized to their ambient read nothing.

 

[lowwall]

Perfect. Thanks.

 

[Gone for diving]

Nice thanks for the real life test,

Now I would love a video of your shop,
looks nice and lots of shiny things!!

 

[Gone for diving]

I have read about sheck and Bowens 1000ft dive attempt,
How Bowen says he was surprised how low his his backgas was, I have wondered if the gauges were oil filled for the depth, but changes the gauge to read psi over surrounding water pressure.....
I mean those guy know how to calculate gas needs,

Just my thought,

 

[lexvil]

Sorry, couldn’t help myself

 

[broncobowsher]

Exactly as expected.

Notice the little cloud of water vapor form for a second as pressure was released? That was from the cooling as the air expanded before returning to ambient temperature. I'm guessing that is a shop compressor without extensive drying and not regulated down dive air.