CO2 tank full?

[Jared]

So, I bought a new 20lb Aluminum cylinder and a set of tank gauges with a regulator. The tank is stamped to hold a maximum of 1800psi. The tank gauge has a range of pressures colored green from 600-1200psi. This green area is labeled "Tank Full".

I got the tank filled for the first time today. Given the "full" range, I was expecting to find the tank filled with 1000psi or so. However, when I got home and put the gauges on, it only reads 575psi tank pressure. Did I get shorted? This is my first CO2 experience... so maybe less than 600psi is all you ever get. It just doesn't seem right.

Any input guys?

Thanks,
Jared

 

[Brian P]

Thats about what mine gets each time, Someone smarter than me can explain why.
Good luck with the tank, I love mine!

 

[NE_Utah]

Mine does that when it is cold. If you set it out in the sun it will go up. It read the gas not the liquid.

 

[Spork]

Mine does that when it is cold. If you set it out in the sun it will go up. It read the gas not the liquid.

Since someone requested the geeky answer...

CO2 pressure will vary by temperature. The hotter it is the less likely it will be a liquid and will build pressure until the pressure is at the liquid state for temperature.
Chart for your viewing pleasure...
http://www.standnes.no/chemix/images/scrshpic/phase-diagram-co2.gif

Basically at a given pressure and temperature it will be either a solid, liquid or a gas. If you take something like water at one atmosphere (sea level) it becomes a solid at 0C (32F=ice cubes) and boils or becomes a gas at 100C (212F=steam). CO2 just does the same thing just at different temperatures.
There's a science experiment they show in school where they basically put water in a container and reduce pressure using a vacuum and the water will boil at room temperature.

 

[Jared]

Thank you Spork. I figured there needed to be some room for safety due to increasing pressure with temperature. It just seemed a bit extreme.

The tank was still cold from being filled when I tested it. Should be interesting to see what it reads today at room temperature.

Thanks,
Jared

 

[cruiseroutfit]

The better way to check the level of your CO2, weight. Next time it is empty, mark the tare weight of the bottle (empty weight with or without reg, just remember which) on the bottle. Then, immediately after a fill, weigh and mark again. Then when you question the contents, weigh it.

 

[muddyjeep]

When I had my 20lb filled for the first time it read 1500 psi after taking it out of
the hot jeep. So temp has allot to do with the pressure.

 

[cruiseroutfit]

...So temp has allot to do with the pressure.

Who knew CO2 would pretend to be an ideal gas

While CO2 is not in fact an actual ideal gas, it behaves much like one, close enough the the ideal gas law can be used to estimate variables under some circumstances (depending on the state of the C02). We were camping in low-teens weather in Dec 06' trying to air-up our tires using a full CO2 bottle, it wasn't having it. Between the cold ambient air and the temperature loss while changing phases, the regulator that normally works great was freezing up in seconds. We had the thing on the radiator of my BIL's Cruiser trying to thaw to no avail. We ended up airing up 12 ~35" tires with my ARB pump

 

[Jared]

Checked it tonight at room temperature... closer to 800psi.