Question regarding keeping air pressure in scuba tank.

[rnln]

Hi guys,

I have read about keeping air pressure in scuba tank multiple times and keep that in mind, but I am confused. The confusing part is why is it opposite with the normal air compressor tank? With air compressor, people recommend to release all air when you are done using it. If leaving pressure in the tank for too long, it will create water in the tank and rust. Similar to when we use pressure to flood our car's brake fluid. I am not sure if it's true or is it's a myth but some say using pressurize method to flood brake fluid will create some water in the break system. Can someone have clear explanation about this?

Thanks.

 

[saxman242]

Basically, the compressors used for scuba remove the moisture from the air, so there's nothing to condense. Standard compressors don't, so they get water build up in the tank which starts corroding the tank.

Brake fluid absorbs water from the air in the reservoir. Has nothing to do with pressure bleeding.

 

[The Chairman]

Brake fluid is hygroscopic and deteriorates as it absorbs humidity and gets cooked as it does its job. There are synthetics out there and I use them.

Keeping air in a tank has to do with physics and keeping water out. Back when we had j-valves, we used to run out of air on a routine basis. If you forgot to close the tank, it was possible for water to be introduced into the tank which caused a huge mess inside.

 

[D_Fresh]

In addition to the above, it is my understanding that keeping pressure in a scuba cylinder (helps) prevents contaminants from getting into the cylinder, ensuring that it remains clean. An air tank for non-diving related usage does not have to be so clean, just drain any water to prevent rust, thereby (over time) compromising the integrity of the tank....

 

[James79]

In addition to the above, it is my understanding that keeping pressure in a scuba cylinder (helps) prevents contaminants from getting into the cylinder, ensuring that it remains clean. An air tank for non-diving related usage does not have to be so clean, just drain any water to prevent rust, thereby (over time) compromising the integrity of the tank....

Just to reiterate from above, non diving compressor tanks need drained due to lack of condensers/filtration. Properly filled scuba tanks will not have any water (and a ridiculously low dewpoint, meaning even if it's cold none will condense inside).
Respectfully
James

 

[D_Fresh]

Just to reiterate from above, non diving compressor tanks need drained due to lack of condensers/filtration. Properly filled scuba tanks will not have any water (and a ridiculously low dewpoint, meaning even if it's cold none will condense inside).
Respectfully
James

Totally agreed , That's why I only said "In addition to the above" as that was already covered. Internal cleanliness of scuba cylinders is very important, especially any cylinders used in partial pressure blending for enriched mixes. That was my only point.

I think we're on the same page James

 

[rnln]

So the key here is "the air is filtered in the scuba tank" right?
Thanks everyone.

 

[James79]

So the key here is "the air is filtered in the scuba tank" right?
Thanks everyone.

Pretty much. Filtered and dried by the breathing air compressor's filter stack and condensers

 

[Nathan Doty]

So the key here is "the air is filtered in the scuba tank" right?
Thanks everyone.

It's completely dry, no water in the air to corrode there interior. If you run a tank completely empty atmosphere will force it's way in, bringing whatever humidity it has with it. As long as there is SOME pressure inside, that will never happen. Unless you're really skilled at shutting the valve at the exact moment the tank pressure just drops to atmo of course...

A shop compressor just... Compresses air and all the humidity with it. It also heats the air, which increases how much water it can absorb. It will be in gas form initially but as soon as it cools it will pool at the bottom of the tank. I keep mine under pressure a lot right now, im working bit often with my new car project. But once a day I drain the water. I also have 2 seperators online between it and my blast tank. After working it for an hour both are full and my gun starts spitting.

 

[BRT]

It's completely dry, no water in the air to corrode there interior. If you run a tank completely empty atmosphere will force it's way in, bringing whatever humidity it has with it. As long as there is SOME pressure inside, that will never happen. Unless you're really skilled at shutting the valve at the exact moment the tank pressure just drops to atmo of course...

A shop compressor just... Compresses air and all the humidity with it. It also heats the air, which increases how much water it can absorb. It will be in gas form initially but as soon as it cools it will pool at the bottom of the tank. I keep mine under pressure a lot right now, im working bit often with my new car project. But once a day I drain the water. I also have 2 seperators online between it and my blast tank. After working it for an hour both are full and my gun starts spitting.

Raising the temperature increases the amount of water it could hold, but the air still has the water it had when it was heated so the RH drops. Raising the pressure reduced the amount of water it can hold, so the RH rises and the some water drops out. If you drain that water shop air is dryer than atmospheric air.