Hygiene - Steel vs. Aluminum

[Packhorse]

Now, what I learned with some older guys here is to avoid leaving tanks with less than 500PSI of air on it. It will be more prom to get corrosion regardless of what tank you use if you are always leaving them close to empty.

Can you please explain how this works?

The way I see it is that at a higher pressure the air will have a higher dew point and it will be more likely for condensation to form. As the tank gets emptied the pressure drops and so does the dew point meaning far less chance of condensation that could cause rust.
Perhaps I have it all wrong.

 

[belgianbrew]

Can you please explain how this works?

The way I see it is that at a higher pressure the air will have a higher dew point and it will be more likely for condensation to form. As the tank gets emptied the pressure drops and so does the dew point meaning far less chance of condensation that could cause rust.
Perhaps I have it all wrong.

What I was told by a dive master, and I'm not sure if this is the real explanation for the mechanics of it, but by not allowing the tank to empty below 200 psi it keeps sea water out.

 

[UnderSeaBumbleBee]

Can you please explain how this works?

The way I see it is that at a higher pressure the air will have a higher dew point and it will be more likely for condensation to form. As the tank gets emptied the pressure drops and so does the dew point meaning far less chance of condensation that could cause rust.
Perhaps I have it all wrong.

I thought the filters took out the moisture so that there was't any in the tank and therefore dewpoint would not be much of a conncern. Am I wrong on that?

 

[belgianbrew]

Sheesh you seem a little on the precious side to be diving, after all, billions of creatures eat, sleep, procreate and defecate in the stuff your swimming in... A little rust is nothing, do you check what is upwind of you before breathing?

Precious?! For your information I learned to dive in Long Island, and dive in the waters of New York City. A far cry from crystal reefs.

 

[BlueDevil]

I've never heard any one question the health aspects of using different metals in tanks?! Given that Jacques Cousteau did a hell of a lot of diving over his lifetime and died at a ripe old age I wouldn't be too concerned that you will get some nasty life threatenting condition from breathing air from a scuba tank!

 

[SparticleBrane]

I thought the filters took out the moisture so that there was't any in the tank and therefore dewpoint would not be much of a conncern. Am I wrong on that?

There's still a small amount of moisture in the gas, however, it is (or should be, if the filters and compressor are functioning correction) so small that it is essentially insignificant. It's measured in ppm.

 

[roakey]

What he means is they don't become positively buoyant when empty.

I don't read "stable and more uniform" as meaning "don't become positively bouyant". I'd still like socaldiver77 to explain what he means by that statement.

Roak

 

[Packhorse]

What I was told by a dive master, and I'm not sure if this is the real explanation for the mechanics of it, but by not allowing the tank to empty below 200 psi it keeps sea water out.

Lesson number one. Dont listen to dive masters (anyone for that matter)unless they can back up what they tell you. Some DM's just re tell old lies with out ever taking the time to understand the reasoning (or lack there of) behind them.

If you have 100 psi of air pressure in a tank how is the salt water going to get into the tank? There is 100 PSI on the inside and 14.5 PSI pressure on the out side. High pressure wants to travel to low pressure not the other way around. Its simple.
As long as there is more pressure inside the tank than outside nothing is going to make its way in. Even if the pressure differential is 10psi. Or if the valve is closed and left closed no matter what the pressure differential.

 

[Mr.X]

As stated by Packhorse - you need evidence. Divemaster in my book, and especially NY = blowhard. I find D'Masters very tiresome. The ones I train are taught not to blow wind.

I will add that having dived NE for decades sometimes people forget to purge the tank valves dry prior to filling it. This is why I always blow out the valves, and especially DIN valves threads before I have anyone fill them. If higher pressure gas goes into a cylinder (even with 200 psi) there could easily be some droplets of water introduced into the tank via high pressure fill gas which could conceivably start some type of corrosive process. As per breathing through Al. or steel. - AL tanks are alloys, not pure AL. Steel tanks the same.

If you are diving NY just make sure to purchase your gas from a LDS who runs a clean shop. It's like restaurants. You got bird poop outside and dirty tables you can easily imagine the quality of the prep. work in the kitchen, or state of the compressor/fill station.

 

[belgianbrew]

As stated by Packhorse - you need evidence. Divemaster in my book, and especially NY = blowhard. I find D'Masters very tiresome. The ones I train are taught not to blow wind.

I will add that having dived NE for decades sometimes people forget to purge the tank valves dry prior to filling it. This is why I always blow out the valves, and especially DIN valves threads before I have anyone fill them. If higher pressure gas goes into a cylinder (even with 200 psi) there could easily be some droplets of water introduced into the tank via high pressure fill gas which could conceivably start some type of corrosive process. As per breathing through Al. or steel. - AL tanks are alloys, not pure AL. Steel tanks the same.

If you are diving NY just make sure to purchase your gas from a LDS who runs a clean shop. It's like restaurants. You got bird poop outside and dirty tables you can easily imagine the quality of the prep. work in the kitchen, or state of the compressor/fill station.

I don't think the DM I was with were blow hards in fact they were actually quite nice. Maybe he didn't have the right way of saying it, but I believe the logic is the pressurized air inside keeps contaminates and foreign matter out. Seems simple enough.