# E.O.T.D - The Mechanics



## Andy D (31 Mar 2015)

Hi All!

I have been reading up on the dreaded 'end of tank dump' but I am struggling to understand the mechanics behind what actually happens. 

Can someone explain please?


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## Jay1 (31 Mar 2015)

Hello Andy from what I understand it all depends upon if the bottle has liquid or gas? 
From this I mean if you have a regulator with one single gauge it gets regulated via a valve so the amount of liquid that is aloud to pass is metered via a orafice. 
Two stage gauges have finer orafices like the ones with a needle valves and solinoids. 
so coming back to your question why suddenly at the end of a co2 bottle rushes and dumps the co2 into the tank?
The idea is based around the working pressures of liquid and gasses. 
Liquid will pass though at a slower rate or whatever rate the regulator is usually set for liquid. 
Gasses on the other hand has a higher working pressure and is more than likely will flow at a faster rate. 
With these in mind, when you come to the end of a co2 bottle the only thing is left in the volume of the bottle is gas!
So unless you have a really fine needle valve to meter the flow the rate of injection, is like a sudden dump of co2 gas more than the liquid would from the start of the bottle.
This is why I have 6.25kg of gas and not liquid. 
Most people opt for liquid because it last longer, and the bottle can hold more co2 liquid for its size. 
The most common bottle FE this has a long suction valve to the bottom of the tank to take liquid first. As liquid is heaver than gas so a FE must be postioned upright.


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## ian_m (31 Mar 2015)

EOTD is something some people spend and inordinate amount of time worrying about something that doesn't affect 99.99% of CO2 users.

It is caused by "cheaper" regulators loosing regulation when CO2 tank pressure drops and releasing the rest of the cylinder uncontrollably into the tank, generally making the fish suffer.

Some regulators are not actually regulators, but in the "gas world" are flow controllers and are either pin holes in a metal diaphragm or a metal sponge, as pressure drops diaphragm bends and metal sponge opens a bit releasing rest of gas. Generally not a problem when used with disposable CO2 containers as in use for welding you get notification due to gas rushing out that cylinder is empty and not a problem for fish as dump volume is quite small. Major issues of course if using a 2Kg of bigger CO2 source as dump volume can be large.

Regulators like this below designed for disposable containers, so EOTD is not an issue.



 

A dual stage (as opposed to dual gauge) does not suffer from EOTD as first regulator drops the 55bar tank pressure to say 10bar and second stage drops pressure to 3bar. The output maintains 3bar as the tank pressure drops from 55bar to 10bar as it starts to go empty. Does not EOTD.

A single stage regulator (cheaper) drops the pressure straight from 55bar to 3 bar and can suffer falling pressure as tank pressure drops, or if you have a cheap regulator may suffer EOTD. My Co2Supermarket regulator starts to drop pressure ie fall in bubble rate when pressure starts dropping. This goes on an for a couple of days and I just change the cylinder. Have watched it drop to zero bubble rate (10bar cylinder pressure) and no EOTD for me.

Please note the pressure in CO2 cylinder (unlike an air cylinder) is roughly constant (55bar) regardless of the cylinder contents as the CO2 is liquid. So you can't reliably work out how much is in the cylinder based on pressure. Hint use a set of scales, a full 2Kg FE is 2Kg heavier than an empty one. . Once all the liquid has gone, only gas is left and it is then the cylinder pressure starts dropping.


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## ian_m (31 Mar 2015)

Jay1 said:


> Hello Andy from what I understand it all depends upon if the bottle has liquid or gas


Sorry Jay but might I correct you in that you have just quoted a load of bollards...Sorry.

The amount of gas drawn off for the use we use always means the regulator works on gas, no liquid involved. There is a dip tube in a fire extinguisher, but volume being used is so small there is b**ger all chance of liquid making up the dip tube. An FE is designed to discharge 2Kg in 30 seconds, we are discharging 2Kg in 100 days....big difference. Try it, open the needle valve full and let CO2 flow, no liquid CO2, no chilling of FE as rate is so small liquid CO2 doesn't stand a chance getting out. It doesn't matter which way up an FE for aquarium use is, I ran mine on its side in a magazine rack for months, no CO2 issue.

If you want something to worry about, you should really run your FE upside down, so dip tube entrance is above the liquid to only gas can ever get to the regulator.

Please don't be offended....


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## Jay1 (31 Mar 2015)

Well the differential of pressures will effect a bottle if it has more liquid than gas or vice versa hence all that moves through the oraffice becomes *gas in the end anyways*.
I just made it simple, there are loads of explaning I could do, but its dangerous even to try and explain as I could cause people to hurt themselves.
TBF the FE is cheap, but not the safest way to use Co2!
In my world liquid and gas pressures are everything especially if you have to nitrogen test at 800psi.

Andy take it however you wish, but getting a two stage regulator with a finer needle valve will regulate anything. 
If the nerds out there wish to use a control set up you can buy a pressure control system build it yourself all it does is mechanicaly senses the working pressures and if it drops below a certain valve it can be switch off via a solinoid valve (MAG vave) inline with the co2 tubing.
Offended Ian? 
"Knowlege is gained when you are offended" unless you are a "coconut" LOL 
Jay


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## Rahms (31 Mar 2015)

fear of EOTD makes people do some very funny things:


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## Andy Thurston (31 Mar 2015)

a full thread of bollards perhaps this will help you understand andy
http://www.airproducts.com/~/media/Files/PDF/company/safetygram-12.pdf
the only truth in this thread so far is eotd is rare in aquatic setups but it does happen


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## ian_m (31 Mar 2015)

Rahms said:


> ear of EOTD makes people do some very funny things:


Love it. 55bar to 39bar to 16bar to 6bar.....


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## Andy Thurston (31 Mar 2015)

Rahms said:


> fear of EOTD makes people do some very funny things:



it would probably be cheaper to buy a dualstage reg some people are idiots


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## Andy D (31 Mar 2015)

Thanks all!


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## genomecop (7 Jun 2015)

Big clown said:


> a full thread of bollards perhaps this will help you understand andy
> http://www.airproducts.com/~/media/Files/PDF/company/safetygram-12.pdf
> the only truth in this thread so far is eotd is rare in aquatic setups but it does happen



Off topic a bit, but that link is certainly a throw back for me. My father who was a nuclear engineer, worked at Air Products throughout my childhood. Smart man. Now I know who I'm going ask to do my CO2 system. Thanks!


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