# Other Aquarium Forums > Equipment and Accessories >  Maximum Pressure CO2 cylinder could withstand?

## AnA

Recently, I went to refill the CO2 for a 5L cylinder. After I had hooked up the CO2 regulator, the dial show 1300psi. This is the highest pressure so far after so many refills. All my previous CO2 refills only up till about 1000psi. 

I know there is a safety valve; it will will let out the CO2 once the limit is reach. But, does anyone know roughly what is the max pressure we could fill up to before the valve pressure limit? Does anyone experience the fill up higher than 1300psi? Of course, more CO2 is good but just worry it may hit the limit and activates the safety valve and may cause some danger eventually. Anyone could possibly advise would be appreciated. Thanks.

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## tawauboy

the safety valve will vent when pressure in the cylinder exceeds 3000psi.

when you observe excessive pressure, you should open the main valve and release co2 until the gauge shows "normal" pressure.

the higher pressure may be a result of the recent heat wave. co2 pressure increases with temperature.

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## AnA

Heat wave may cause a slight increase in pressure. But for my case, I just refilled the CO2 cylinder and it shows 1300psi which is 300psi more than the "normal" 1000psi. Anyway, if the safety valve limit is 3000psi, then I feel safe now. Thanks.

Anyone, CO2 pressue dial showing reading more than 1300psi? What is the max value you have ever encountered?  :Wink:

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## lEddyl

here's a nice article

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## AnA

Thanks Eddy for sharing such wonderful article. Anyway, I enjoy reading it.  :Well done: 

So, the higer pressure was really due to the temperature as I put the newly refilled cylinder in my car boot. Luckily nothing happen. 




> here's a nice article

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## AnA

I had been a few days since I refilled the CO2. But, the pressure still indicates 1300psi. I think the temperature should have been stabilized and reached room temperature and should fall back to about 1000psi. Humm...maybe the vapour pressure is still high? If vapour is more; which means liquid is less? So, am I getting less CO2 out of this refill? I think I better get a weighting machine to weight the tank. 

Next time, I will weight the CO2 cylinder before and after the refill to determine the actual amount of the CO2 in the cylinder.

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## KeIgO86

the saturation pressure of CO2 only depends on temperature. That pressure changes almost instantaneously with temperature. If the pressure is more than saturation pressure at that temperature it means that: 

1) the person refilling your CO2 is so generous he pumped so much CO2 in that all the CO2 in your cylinder is in the compressed liquid state. (highly unlikely and very dangerous)

2) your gauge is faulty. (more likely)

3) the weather is really warm these days (very likely too)

And just some more info, more vapour does not make the pressure inside the tank higher or lower. As long as there is 1 drop of liquid CO2 left in your cylinder, the pressure gauge should read the same saturation pressure at your tank is just refilled.

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## AnA

Thanks KeIgO86 for your precious information. 

1) The person could be generous. Because, I told him about Soxal and my CO2 lasted long time, maybe he wanted to get a loyal customer and pump more. That day when I release the main valve without connecting anything to it; the liquid CO2 zoom out instead of CO2 gas. How, it is dangerous? Please advise. Thanks. 

2) The CO2 regulator is new and beside, I use another dial to check and it shows the same reading.

3) I ask my brothers about their CO2 cylinder pressure and all showing about 1000psi... but one of them showing 375psi... guess not even one dot of CO2 left; just co2 gas?

So, as long as only 1 drop of liquid CO2 left in your cylinder, the pressure indicator should read the same saturation pressure at your tank is just refilled. Roger that and thanks.  :Smug: 




> the saturation pressure of CO2 only depends on temperature. That pressure changes almost instantaneously with temperature. If the pressure is more than saturation pressure at that temperature it means that: 
> 
> 1) the person refilling your CO2 is so generous he pumped so much CO2 in that all the CO2 in your cylinder is in the compressed liquid state. (highly unlikely and very dangerous)
> 
> 2) your gauge is faulty. (more likely)
> 
> 3) the weather is really warm these days (very likely too)
> 
> And just some more info, more vapour does not make the pressure inside the tank higher or lower. As long as there is 1 drop of liquid CO2 left in your cylinder, the pressure gauge should read the same saturation pressure at your tank is just refilled.

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## AnA

I just purchased a weighting machine from IKEA. The weight of my 5L CO2 cylinder is 13kg. Next time, I will weight it before and after the refill. Anyone had tried to weight their 5L CO2 tank could advise too?? 

One shop told me that normally refiller will pump about 4 to 5kg of CO2 in general. Well, we find out in the next refill.

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## KeIgO86

1) Liquid CO2?! Could you elaborate? Unless you opened the valve when the cylinder is isn't sitting upright, there should not be any significant liquid CO2 spilling out even if the person really did fill the cylinder beyond the saturated liquid pressure. The pressure needed to compress liquid even by 1cm cube is so great that it will probably deform your cylinder or even cause it to explode before you even have a chance to bring it home.

You may have mistaken it for water vapor condensation and immediate evaporation when the CO2 was rushing out from your main valve. This occurs because of the low temperature produced by rapidly expanding CO2 gas. I would still think that the person doing the refill did not over do the refill as it will risk an explosion. He wouldn't want to risk losing a loyal customer that way.

2) If the gauges are in working condition, the culprit should be warmer temperatures. Do you place your cylinder beside a chiller or in the sun?

3) Yes, you will notice that it takes a long time after your refill before the gauge pressure starts to drop. But once it starts dropping, it empties out quite quickly because all that is left in the cylinder is CO2 gas.

Hope this helps.

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## tawauboy

if the pressure gauge still shows 1300+ psi, i would advise you to open the main valve and release some of the co2. let the pressure drop to 1000+ psi.

over filling a co2 cylinder is dangerous. a fully filled cylinder should have about 2/3 full with liquid co2.

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## AnA

Yes, it is liquid zooming put when I release the main valve and the cylinder was in up right position. I do this immediatedly fews hours after refilling and when taken from the car boot. Guess the temperature was still higher than normal then. Check it today and it still showing 1300psi. 

Thanks tawauboy for the advise, I will try to release the pressure to 1000psi when possible.

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## essabee

When CO2 gas zooms out - the rapid fall in pressure, therefore the temperature, will solidify some of the gas into colloidal particles and you would perceive this mixture as liquid.

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## TBoss

my new bought cyliner reads 1100psi... is it ok?

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## drwatson5567

a fully filled cylinder should have about 1/3 full with liquid co2 drwatson5567 

*How much liquid is in a "full" tank? Why not fill it up?* 
A "full" tank contains about 34% liquid CO2. If it is filled any more, the CO2 will become very sensitive to temperature changes, with a small increase in temperature causing a large increase in pressure. This is a dangerous situation which is avoided by only partially filling the CO2 bottle. 
One cubic inch of water weighs 0.577 oz and the specific gravity of liquid CO2 is 1.977 gm/cc so one ounce of liquid CO2 has a volume of 0.877 cubic inches. CO2 bottles generally have a full-fill to volume ratio of about 2.57 cubic inches per ounce of CO2, so that one ounce of CO2 will take up 0.877/2.57 = 34% of the total volume of the bottle. The figure of 68% is often quoted as the volume of liquid in a full bottle, but this error probably stems from translating "ounce" into volume using water as the standard. Water is 1.00 gm/cc, or about half the density of liquid CO2 so that if a CO2 bottle is filled to its rated capacity with water, it will be 68% liquid by volume.

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