# When is there danger of an end-of-tank CO2 dump?



## fishstein (Dec 12, 2005)

I have a 20lb tank with high quality dual regulator and needle valve. My tank was originally at about 900 PSI on the primary regulator, now after many months it's at about 300 PSI on the primary regulator, with a steady output of 60 PSI on the second regulator, which is controlled by a quality needle valve.

At what point is there a danger of end-of-tank dump?

Also, is there still a danger of end-of-tank dump if you use a quality needle valve? Won't the needle valve prevent this?

Is there as much danger of an end-of-tank dump with a smaller CO2 tank? I plan on switching to a 10lb tank when this tank is up, just to save space. With a solenoid it will last as long as my 20lb tank without one.

Thanks for your thoughts, I don't want to take out all of my fish because of a CO2 tank dump!


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## yoink (Aug 31, 2005)

You should change that tank immediately. Once the pressure starts to drop from the regular 800-900 psi it will continue to drop steadily. After the pressure gets too low to be regulated, it will pour forth from your needle valve causing a dump. The needle valve will help a little with the dump, but certainly not prevent it. I change my tank once the pressure starts to drop. I'm not sure what the pressure has to be before a tank dump, but I think it is pretty close to what you have now.


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## hoppycalif (Apr 7, 2005)

I have read that the "end of tank dump" problem was largely experienced back in the dark ages when folks didn't use good needle valves to regulate the flow. So, I doubt it happening to you. But, the dropping pressure means there is no more liquid CO2 in the tank - it is almost empty. Use that as a good advance warning that you must very soon find a time to get it refilled.


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## JinxXx0085 (Jul 2, 2005)

I'm a newbie!! 
What is "end of tank dump"?


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## Laith (Sep 4, 2004)

If you have a decent regulator and needle valve, you will never experience an end of tank dump. I've been using pressurized CO2 for years in many tanks and never witnessed it, even though I often let CO2 tanks run down to zero pressure.

And I don't know anyone else who uses CO2 who has experienced it either. I think it may have been linked to the early days of using pressurized CO2 when the regulators/needle valves available were not quite made for the use we need them for...


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## John N. (Dec 11, 2005)

JinxXx0085 said:


> I'm a newbie!!
> What is "end of tank dump"?


Hehe, end of the tank dump refers to Pressurized CO2 gas suddenly being released into the tank. As already stated, as CO2 in the cylinder becomes low it turns from a liquid into a gas. The gas then can "dump" into the tank when the overall cylinder pressure falls. The excess CO2 dumped into the tank can cause the pH to fall rapidly and kill fish.

*Along the same lines of this thread, who has experience CO2 End of the tank dumping?*

-John N.


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## JinxXx0085 (Jul 2, 2005)

Thanks John N. for the explanation! That's definitely something new to me.


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## John N. (Dec 11, 2005)

Sure no problem. Though as already noted, this doesn't seem to happen as regularly as in the past possibily due to the better regulators that are offered now. Ah, the hobby is ever changing.

Still we can't rule it out, maybe it does happen still, but I haven't experienced it and haven't heard anyone else recently having this problem. But maybe someone who has had this issue will chime in.

-John N.


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## Bert H (Mar 2, 2004)

I haven't ever personally experienced this either. I do let my tanks typically get down to around 100psi before I go fill them back up again. Knock on wood, so far no problems. I tend to agree that perhaps this was a bigger problem in older days.


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## Rex Grigg (Jan 22, 2004)

It can and still does happen. Not as much though. But you really have to understand how a needle valve works to know that it can still happen. Once the liquid CO2 is gone the high side pressure (on the needle valve) can go up quite a bit higher than it was. This in turn effects the low side pressure and does allow more gas into the tank.


I have actually seen this start to happen on one of my tanks. I was watching and testing and within an hour the CO2 levels in the tank nearly doubled. Now this may or may not cause a problem depending on any number of factors.


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## hoppycalif (Apr 7, 2005)

Rex Grigg said:


> It can and still does happen. Not as much though. But you really have to understand how a needle valve works to know that it can still happen. Once the liquid CO2 is gone the high side pressure (on the needle valve) can go up quite a bit higher than it was. This in turn effects the low side pressure and does allow more gas into the tank.
> 
> I have actually seen this start to happen on one of my tanks. I was watching and testing and within an hour the CO2 levels in the tank nearly doubled. Now this may or may not cause a problem depending on any number of factors.


REx, I don't agree. A regulator is designed to hold the downstream pressure, the set pressure, over a wide range of input pressures. The downstream pressure will never be proportional to the upstream pressure. Then, when the liquid has all evaporated into gaseous CO2, the pressure in the bottle can only go up if the temperature of the bottle goes up, and it takes a big change in temperature to have much effect, since it is the absolute temperature ratio that affects pressure: 70F = 530R (absolute temperature), so if the temperature goes to 100F = 560R, the pressure ratio is only 560/530 = 1.05. Even though the pressure ratio goes up as a power of that temperature ratio, it is a near 1 power. The needle valve can't tell that there is no liquid in the tank, so it holds the flow rate as it was, proportional to the set pressure of the regulator. Thus, no CO2 dump.

EDIT: I just realized how a dump can occur: When the bottle pressure drops too far, as the gas is used up, the regulator no longer has enough pressure supplied to it to control the output pressure, so it could open wide open, thus allowing the output pressure to more than double, and the bubble rate to also more than double. But, most of us don't have nearly perfect CO2 diffusers or reactors. A large increase in bubble rate will most likely result in only a small increase in ppm of CO2 in the water - a Rex style reactor will burp the excess CO2, a disc diffuser will make larger bubbles, wasting CO2, etc. So, while the dump would occur, the effect would likely not be a catastrophe.


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## Smokin_Cache (May 22, 2006)

Thought I might add something to this old thread. I work with regulators everyday. (Instrument tech.) And worked for a dry ice company for five years. I know a little about CO2 and regulators. I am new at putting the CO2 in an aquarium though. First off a regulator is nothing more than a automated valve. Output pressure falls valve opens, output pressure increases valve closes. The regulators used for CO2 bottles rely on spring pressure minus output pressure to close the valve. The only role the input pressure plays is the small amount of force it places on the end of the valve plug. This force pushes in a manner to open the valve. So there is a direct relationship between output vs. input pressures, but I don't think anyone will have a gauge accurate enough at home to see this. I don't understand how an end-of-tank dump could happen. Well maybe, lets see as your tank pressure gets low the valve must open more to keep the output pressure at setpoint. So it opens further than normal and for some reason demand decrease ever so slightly and the valve sticks in this abnormally open position and can't close. This would cause output pressure to increase. Thus increasing flow rate. I think that is the only reason a "dump" would occur. Faulty equipment. Just my opinion.

When the liquid is gone the tank pressure will not rise. Nothing is free!! Temp rise is the only thing that would cause this. Unless your were filling the bottle of course.

Any other opinions?


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## Nicholls57 (10 mo ago)

Smokin_Cache said:


> Thought I might add something to this old thread. I work with regulators everyday. (Instrument tech.) And worked for a dry ice company for five years. I know a little about CO2 and regulators. I am new at putting the CO2 in an aquarium though. First off a regulator is nothing more than a automated valve. Output pressure falls valve opens, output pressure increases valve closes. The regulators used for CO2 bottles rely on spring pressure minus output pressure to close the valve. The only role the input pressure plays is the small amount of force it places on the end of the valve plug. This force pushes in a manner to open the valve. So there is a direct relationship between output vs. input pressures, but I don't think anyone will have a gauge accurate enough at home to see this. I don't understand how an end-of-tank dump could happen. Well maybe, lets see as your tank pressure gets low the valve must open more to keep the output pressure at setpoint. So it opens further than normal and for some reason demand decrease ever so slightly and the valve sticks in this abnormally open position and can't close. This would cause output pressure to increase. Thus increasing flow rate. I think that is the only reason a "dump" would occur. Faulty equipment. Just my opinion.
> 
> When the liquid is gone the tank pressure will not rise. Nothing is free!! Temp rise is the only thing that would cause this. Unless your were filling the bottle of course.
> 
> Any other opinions?


Ive never understood why it should happen other than equipment failing. Co2 psi on the cylinder can be 1000psi or 70psi if the regulators set to allow 60psi as on my fzone the low side it will adjust to maintain that regardless of the tank psi. However if some crud gets into the diaphram and the valve sticks there might be a problem but a good regulator should cope. An interesting note is that on fzones website they make it clear only to use water in the bubble checker not oil.


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