Shop drains tank before fill

[Gone for diving]

There is something to be said for tradition, I'll look through Churchill's quotes and get back to you.

Can someone explain to me, the reason for tank rolling like this?

Is it because not patient enough? To let it mix?
Unless there is a ball brg like a paint can, I don't see how rolling works.

 

[rjack321]

Can someone explain to me, the reason for tank rolling like this?

Is it because not patient enough? To let it mix?
Unless there is a ball brg like a paint can, I don't see how rolling works.

If you have a small slow compressor like me (100L/min) you end up with hot air on top of cooler O2. The force of the air through the dip tube isnt remotely close enough to mix the tank. Takes at least overnight to mix. Tall narrow bank cylinders are even worse.

Lay the tank down, no rolling really required, and the surface area between the air and the O2 is more than double. Mixing happens in ~10mins. Rolling slightly accelerates this, but the real difference is the surface area between the layered gases. It's a heat layering effect, not due to molar gas density. It doesnt happen when filling fast with banked gases or faster compressors (although the tank still gets hot and has to be topped off)

 

[Pavao]

I see this effect is more pronounced in smaller tanks, which seems counterintuitive. When partial pressure filling 2/3L rebreather bottles with trimix, analyzing it right after fill, you get a reading with the bottle standing up, flip it upside down and you’ll get a wildly different reading. Not so much with larger cylinders like doubles.

 

[Gone for diving]

If you have a small slow compressor like me (100L/min) you end up with hot air on top of cooler O2. The force of the air through the dip tube isnt remotely close enough to mix the tank. Takes at least overnight to mix. Tall narrow bank cylinders are even worse.

Lay the tank down, no rolling really required, and the surface area between the air and the O2 is more than double. Mixing happens in ~10mins. Rolling slightly accelerates this, but the real difference is the surface area between the layered gases. It's a heat layering effect, not due to molar gas density. It doesnt happen when filling fast with banked gases or faster compressors (although the tank still gets hot and has to be topped off)

If you have a nitrox stick, I assume mixing is not a problem.

Your saying with partial pressure mixing?

 

[tursiops]

They also fill the tanks in a big tank of cold water.

Not a best practice anymore.

 

[NitroxSam]

Not a best practice anymore.

I'm not really sure why they do it. I was always concerned about water getting into my empty tank through a wet fill whip, esp my steels.

 

[tursiops]

I'm not really sure why they do it. I was always concerned about water getting into my empty tank through a wet fill whip, esp my steels.

It used be thought that the cold water allowed fast fills by keeping the gas cold too. Tests and calculations show this is a minor positive effect, whereas water in your cylinder is a major negative effect. Good fill stations don't do this.

 

[Wibble]

Shirley a tank filled in a water butt must cool down far more quickly than one in air?

Provided the gas connections are done and pressurised out of the water, there’s no chance of water ingress? Obviously talking about DIN not Joke connectors.

 

[tursiops]

It used be thought that the cold water allowed fast fills by keeping the gas cold too. Tests and calculations show this is a minor positive effect, whereas water in your cylinder is a major negative effect. Good fill stations don't do this.

Somebody was confused by my post.
I'll say it differently...
The cooling effect of a water bath is minor, but the possibility of water entry to the tank is major. It is a tradeoff, and today water baths are not considered best practice.

 

[Gone for diving]

Somebody was confused by my post.
I'll say it differently...
The cooling effect of a water bath is minor, but the possibility of water entry to the tank is major. It is a tradeoff, and today water baths are not considered best practice.

Hook up the tank, pressurize the whip,
Open the tank, set in the water,,, nothing will get into the tank,
Even a tank monkey should figure that out.

I always figured that not overheating the tank its self and exploding reasons was the main reason, to use water.

When I fill, I normally bulk fill, then top of hrs or a day later,
But occasionally I don't have the luxury, and will drop the tank in a 5gal bucket, so tank is 2/3ish covered.... makes a huge difference especially aluminum tanks.