CO2 Tanks

[stranglehold]

Are CO2 tanks filled with gas or liquid?

I was wondering if a 5lb tank could be filled off of a larger tank like oxygen can be.

[Franz]

The short answer is liquid under a head of vapor, under normal circumstances, just like most refridgerant gasses.
The second answer is yes, assuming you have the proper equipment and know what you are doing. Co2 cylinders need to be chilled first, unlike O2 cylinders. As long as there is still liquid in the cylinder you are charging from, you can charge the 5# cylinder. Co2 does not require cascading like O2 and Helium.

[Roger]

Pressure of HP CO2 cylinders containing liquid CO2 changes a lot with small temperature changes. By chilling the cylinder to be charged a pressure differential is created that will drive CO2 from Source cylinder to recieving cylinder. If the CO2 transfered is in gas state much slower transfer rate will take place so less CO2 will probably be transfered.

Must judge state of charge by weight not pressure. Over charged CO2 cylinder contain too much liquid volume leaving not enough gas volume to handle liquid volume increase due to possible temprature increase.

Commercially CO2 cylinders are filled using transfer pump to move liquid CO2.

Liquid CO2 is also stored at low pressure and temperature in vacuum insulated container called a Dewar.