# Filling A C02 Cylinder (pressure / Weight)

#### Nick72

##### Well Known Member
I've got a 3 Liter (6.6 lbs) C02 cyclinder.

It's 2.8 KG empty

1 Liter of liquid CO2 weighs approximately 1KG (1.024kg dependent on temperature (15c) and pressure(300psig)

You only fill a C02 cylinder to 68% (leaving 32% safety factor for gas expansion)

So filling my 3 Liter, 3kg * 0.68 = 2.04Kg + cylinder weight 2.8Kg = full weight 4.84Kg.

I made my LFS weigh my cylinder as they gave it back to me = 4.056 Kg.

That's only 83% charged.

Am I missing something here?

Also, everyone talks about a full cylinder having a PSI of 800-1000.

My cylinder is marked:
"PW124Bar" = Charging Pressure 1798 PSI.
"PH186Bar" = Testing Pressure 2697 PSI

So shouldn't my Charged Pressure on a full cylinder read 1500+ PSI ?

This is my first refill, so please feel free to point out what I'm not understanding.

#### Zniaz

##### Valued Member
Well, although i don't have much experience in physics, I will say that I am pretty sure the CO2 isn't liquid, I think its just compressed gas inside the tank, so i am not fully sure if the LFS did something wrong or not.

Also, just trust your LFS. I am sure they are experienced and have done tons of refills before, and i reckon you should do much thinking on wether they did something wrong, unless something goes wrong in your tank. At this point, i would say that there isn't any problem, although your math is right, I would have faith in the LFS staff as they probably know what they're doing.

~Zniaz

#### Nick72

##### Well Known Member
Got the C02 cylinder home this evening and plugged it back into my system..

My regulator is saying 900 PSI.

When I bought the cylinder and plugged it into my regulator it said 1000 PSI.

So seems this refill is not as full as when I originally bought the cylinder.

That and the math strongly imply my LFS aren't fully filling.

It's not the money, they only charged \$8.50 USD (equivalent), I just don't want to be taking the tank back too often.

#### Nick72

##### Well Known Member
I'm giving this a bump as I'm far from certain that I'm correct about:

A) the 3 Litre cylinder should weigh CO2 weight 2.04Kg + empty cylinder weight 2.8kg = full weight 4.84Kg

B) the cylinder should be filled to the stated 'Charging Pressure' of 124 Bar / 1798 PSI

Anyone here have good working knowledge of C02 cylinders?

#### CHJ

##### Valued Member
Zniaz said:
Well, although i don't have much experience in physics, I will say that I am pretty sure the CO2 isn't liquid, /QUOTE]
Under pressure it is. In paintball you have 2 types of guns (or did in the old days) gas and liquid.
Also my dad says that when he was in college one of his classes had a glass cube with thick walls so you could see the liquid CO2 inside it.

For CO2 I just swap my bottle at the brew supply place. I don't even weigh it. If you think the LFS is doing it wrong you could hit a welding supply/gas supply store and ask them.
When I was in college our team would simply hang the bottles on a scale when we filled them.

#### aniroc

##### Well Known Member
@Nick72

You are assuming that 1 liter CO2 weights approx 1 Kg as if the density is 1 gram per mililiter. Not true.
It depends on the pressure. As a fact, at 14C and 725 psi, liquid CO2 has a density of 827 g/L which is lower than water.

Indeed, a full cylinder has 1000psi. A half full cylinder also shows 1000psi. It is only when all CO2 inside the canister is in gaseous form (no more liquid) that the pressure starts dropping and single stage regulators damps.

#### Nick72

##### Well Known Member
aniroc said:
@Nick72

You are assuming that 1 liter CO2 weights approx 1 Kg as if the density is 1 gram per mililiter. Not true.
It depends on the pressure. As a fact, at 14C and 725 psi, liquid CO2 has a density of 827 g/L which is lower than water.

Indeed, a full cylinder has 1000psi. A half full cylinder also shows 1000psi. It is only when all CO2 inside the canister is in gaseous form (no more liquid) that the pressure starts dropping and single stage regulators damps.
Yeh, I've spent the last few hours reading up on this.

C02 under pressure can be in a liquid form from -57c up to 31.1c.

And you need to know the temperature of your stored C02 to know the weight.

As you say the weight varies tremendously at differing temperatures.

As I've no way of estimating the temperature of the liquid CO2 in my cylinder, I can't see how I can accurately tell how full my cylinder is based just on weight.

Think I'll give up on this.

#### JDWebb01

##### Valued Member
Here's what I know about Co2 bottles. I have two 5lb bottles that get filled by my local homebrew store to about 900-1000 lbs. I am a home brewer with 4-keg tap bar, and one bottle is enough to last almost 10 months, thats keeping 4 kegs pressurized and for carbing them at 40lbs pressure for 2 weeks as well. The other 5lb bottle will be used for my aquarium. I'm guessing it will use far less Co2 than my keg setup and will probably last...well, years at 1 bubble per second. Just my two-cents!