# Max refilled weight of Co2 tank



## ltsai (Sep 24, 2010)

Hi,

I'm pretty confused about the final weight of a co2 tank after a refill.

Given the tare weight of the tank, should a 5# tank be filled with 5# liquid co2 or up to 68% of the weight?

It seems that we should weigh the tank after a refill and the tank should weigh tare + 5lb?

From Cornelius, I see the following description:


> CO2 cylinders are allowed to be filled to a legal maximum “filling density” of 68%. The term “filling density” desig- nates percent ratio of weight of liquid CO2 in cylinder to weight of water at 60° F that the cylinder will hold.


From Catalina Cylinders:


> We at Catalina Cylinders have heard many times that it is not fair that a CO2 cylinder is deemed full at only 68% of its water capacity, that there appears to be 32% of its water capacity that is not being used, or wasted, and that this capacity not being used could be used for extended service life of one CO2 charge. This 32% is not spare, or wasted, capacity.


And from Australia: http://kegking.com.au/faq.html


> How do I know how much gas I've got left?
> - The best way to do this is by using your scales. You will also need to know the weight of the cylinder when it's empty. Most CO2 bottle are referred to using the weight of liquid CO2 it holds. So lets say you have a "5kg bottle". This doesn't mean the cylinder weighs 5kg, it's simply means that the cylinder will hold 5kg of liquid CO2 when full.
> 
> What size is my gas cylinder?
> CO2 cylinder in Australia can only be filled to 66% of their water capacity. What does that mean you ask? Well lets say you have a 4Litre cylinder. Hypothetically if you take the valve out and fill it with water you will fit in 4kg of water to the top. So this cylinder would be considered full if you fill it up to 66% of this capacity with CO2. So 66% x 4.0 = 2.62kg. So your cylinder has a rated capacity of 2.64kg of CO2.


The tanks should be rated for 5lb and it should fill up with 5lb of liquid co2?

What about this "68% of its water capacity"? Is this important?

I live in Asia, so our tanks are measured in Litres and not by weight. A Litre of CO2 is slightly heavier than 1 litre of H2O. 

Thanks!


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## tunatime (Aug 1, 2012)

Your not going to get 5lb of gas in a 5lb tank you need some room for expansion. If you filled a tank to the Max then stuck it in say a hot car it could blow
You should get about 4.5-4.75lb of gas in a tank


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## Bettatail (Feb 12, 2009)

This is a good one!
the "5lb" for 5lb co2 tank, is the water weight when the tank is filled with water.

you destroy the "common sense" here, now I know whoever think a 5lb co2 tank should hold 5lb of co2, is wrong.
I was wrong too, thanks for the info, now I know a 5lb co2 tank only take in 3.5lb of co2 when it is "full"(safe/standard ratio), 68% of water capacity/weight.

here is another good read, click on the reference tag when the link open.
http://www.lelandgas.com/cylinders.aspx


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## ltsai (Sep 24, 2010)

Here's another link:
http://www.catalinacylinders.com/co2.html



> Part No: B5
> Empty Weight (lbs / kgs): 6.3 / 2.9
> CO2 Capacity (lbs / kgs): 5 / 2.3
> Water Capacity (cu in / lbs / liters): 203 / 7.4 / 3.4


5/7.4 = 68% of water capacity.

Does that mean 5lb rated tank actually has about 7.4lb of water capacity or can contain about 3.4L of water when fully filled?


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## Bettatail (Feb 12, 2009)

ltsai said:


> Here's another link:
> http://www.catalinacylinders.com/co2.html
> 
> 
> ...


if that is the case, I will fill my 5lb tank 5lb of co2,


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## HD Blazingwolf (May 12, 2011)

well scale wise, i get about 4.5 lbs from my local welding shop. weight of tank is roughly 7 pounds empty and 11.5 pound full. it is a 5lb tank

so either im lucky, or they know what they are doing. my tank stays at about 800 psi so i dno't think its overfull


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## PlantedRich (Jul 21, 2010)

This is likely to be one of those cases where we are overworking the question. A good thought as a point of interest but not likely to have much practical value. We as hobbyists often ask questions nobody else asks just because we only nibble around the edges of the task. 

Does anybody who knows the price of CO2 and the price of the labor to fill a tank actually think the dealer will bother to save a few cents on the CO2? If you go to some specialty shop who caters to hobby types, you may get the new kid who doesn't fill it right but that will not happen if you go to a shop who does this work all the time. There is just no profit for a business that sells thousands of pounds of CO2 weekly in trying to short our small portion of the market on a pound of a product he buys so cheap. 

Just the idea that we can't tell when the tank is full by picking it up shows that we are not really very far into this game. The real users of CO2 in quantity can tell by the feel of the tank. I'm not asking ANY of them if they shorted me! I consider myself lucky they are willing to put up with the nuisance of selling one tank over the counter!


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## ltsai (Sep 24, 2010)

They may not short you on purpose but could be due to ignorance. 

I am a new user of pressurized co2 since I got so frustrated with algae and diy. 

I am thinking that a 5lb tank is indeed rated to hold 5lb(weight/mass) of liquid co2 and has factored in the 68% safety margin of water capacity (volume). 

From Cornelius:


> A 10-pound cylinder is being filled, tare weight stamped is 20-pounds, 6-ounces. With the cylinder on a scale, pump liquid CO2 into the cylinder until the scale reads 30-pounds, 6-ounces.


Sounds reasonable?

But in Asia and Australia, our tanks are measured in litres hence we need to apply the safety margin.

LFS typically refill from a bigger tank and sometimes they do not use a scale. I don't consider them real users of co2.

My lfs tops up by feeling the weight of the tank and by showing me the regulator gauge reads 1000 PSI, which is incorrect. PSI can change because of temperature and does not indicate that the tank is full.

I own a 1l tank and I weigh it when I got home. It contains only about 200-300g of co2. The tank only last about 7-10 days when I run it 24/7. I do not have a bubble counter but by using the "bubbles/pop" in the diffuser cup, I reckon that I am using about 1 bubble per 2-3 seconds. This is for a 2ft tank. 

It looks like I need to find another place to top it up and check for leaks again.


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## kevmo911 (Sep 24, 2010)

Disclaimer: This is a shameless plug for dual stage regulators.

*If* your CO2 filling station (welding supply shop, etc.) knows what they're doing - and it's not like it's difficult - they'll fill it. It will only start to decrease in pressure when less than 5% of the total volume of CO2 is reached. At that point, the cylinder pressure gauge on a regulator will start to decrease.

With any dual stage regulator, that will mean a negligible increase in working pressure. With a quality single stage regulator, that will mean an anywhere between negligible and minor increase in working pressure. With any retail all-in-one regulator setup, that will mean a significant increase in working pressure, enough to kill a lot of fauna if you're not careful.

The point? It doesn't matter how much your cylinder weighs if you have any dual stage, or a decent single stage, regulator. Just check on the working pressure every few days. When it starts to drop, refill.

Or, you could regularly weigh your cylinder, and take it out to refill at the point at which you determine it's empty enough. Your call.


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## PlantedRich (Jul 21, 2010)

Quote --LFS typically refill from a bigger tank and sometimes they do not use a scale. I don't consider them real users of CO2.

My lfs tops up by feeling the weight of the tank and by showing me the regulator gauge reads 1000 PSI, which is incorrect. PSI can change because of temperature and does not indicate that the tank is full.

This is my point on getting the refill done where folks are trained! We are such a small user when it comes to CO2 that there is far more chance of running into somebody who knows nothing when you go to the specialty shops like LFS or home brew shops. 

If you want the tank filled right, don't go the place where two or three guys drag tanks out of their backseat to refill. Go to the place where a truck brings in 25-30 tanks at a time to be filled daily. Those are the folks who really USE the CO2. In the hobby, we only PLAY with CO2. If the place doesn't have a dock for trucks, it is likely not the best place to get refilled.


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## dmagerl (Feb 2, 2010)

I've filled my tank up at 3 different places.

First at a party rental store that rents kegerators. I have to ask for a "paintball refill" which sucks liquid into the tank vs a "kegerator refill" which is gas only. He would open the valves and let it hiss until things stopped. No weighing is used. Typically the tank is 2-3 lbs heavier when I weigh it at home. I had started leaving the empty tank out in the sun to warm it up and then cracking the valve to let it depressurize, then putting it in the freezer before bringing it to the store. This resulted in 5 to 6 lbs of CO2 in the tank.
He definitely didnt fill it correctly and was always short.

I then went to a fire extinguisher store. The tank came back 10lbs heavier. BTW its a 10lb tank. They definitely knew how to fill a tank.

Then I went to a welding gas supplier which does tank exchanges. New tanks are always 10lbs heavier than their tare weight. They know how to fill a tank too.

So my experience shows that a 10lb CO2 tank is filled to capacity with 10lbs of CO2.


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## ltsai (Sep 24, 2010)

What about the option of leaving at the lfs for a few days while they "send" your tank to the factory.

Is it properly filled too?


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