[Clinton Parsons]

I still think it's worth the investment to just get pressurized, but this is a neat science project and I wanted to say I am very impressed at your ingenuity. This is the fanciest DIY co2 project I have ever seen. Good job!

 

[kinsa]

The tee serves as a one-way valve, it prevents the soda solution to go to the acid bottle. You can actually remove the tee and the long section of the tubing and the system will still work.

The length of the tube after the tee is not important, the main purpose is to make sure that the acid goes directly to the soda solution and not get stuck on the side of the bottle. I've removed mine and it doesn't make any difference.

How much does a 250 ml citric acid weigh? Your acid solution is weaker compared to the "normal" mixture of 200 gm acid/600 ml water. This would explain why your system is a bit slow or unable to maintain the initial 10 psi pressure - assuming that your system is leak free.

Note that for a 1 bps output rate, a leak of 0.1 bps is significant and is not easily detectable by soap solutions. That's why observing the movement of the acid level on the tubing between the bottles overnight is the best way to determine any small leaks. This is especially true for the non-flat bar setups as there are more connection points that could possibly leak (3 per bottle compared to 1 per bottle).

Here's a simple thought experiment: assume that the acid bottle is half-filled with acid and pressurized to 1 atm (14.7 psig), the baking soda bottle is empty and is also pressurized to 1 atm, the needle valve is set to regulate at 1 bps and the output is exposed to atmosphere. We assume that the needle valve is a regulator and not a flow restrictor, i.e no matter what the pressure differential is between the input and output ports the output flow will remain constant.

As soon as the needle valve is opened to 1 bps setting, the acid solution will start flowing to the soda bottle because there will be a slight pressure difference between the two bottles. The rate at which the acid will flow will be lower than 1 drop/s (assuming 1 bubble is equal to 1 drop) due to the compressible nature of gases.

Closing the valve will also cause the acid to stop transferring to the soda bottle. This is because the pressure between the two bottles will equalize.

Once the valve is opened, the acid flow towards the soda bottle will continue until it is exhausted.

Still clear so far?

Now lets assume we have a leak on the acid bottle side, let's say 0.01 bps or 1 drop per 100s. The acid will flow once we open the needle valve but over time the rate will slow down until it stops completely. The time it takes for the flow to stop will depend on the rate of the leak.

If the leak is on the soda side, the flow will still continue until the acid is exhausted. This time the flow rate will be quicker. Note the acid flow will still be there even if the needle valve is fully closed.

So the only way for the system to stop generating bubbles is (1) there's a leak on the acid side and (2) the minimum pressure required to produce bubbles at the output side (after the needle valve) is higher than the pressure on the acid bottle. Do note that the pressure of a gas is inversely proportional to the volume that it occupies (if the volume of the gas in the acid bottle has doubled in size, the pressure it exerts is reduced by half).

Now lets make this thing interesting by adding baking soda to the soda bottle.

Lets assume that 1 bubble of gas is equivalent to 1 drop acid solution and 1 drop of acid will react with 1 drop of soda to produce 4 bubbles of CO2 for 4 secs (1 bps of gas for 4 secs).

So for a drop of the acid solution, 5 bubbles of CO2 comes out at the valve within 5 secs.

Decreasing the concentrations of either the soda or acid solutions will reduce the rate of CO2 production. This reduction of CO2 production will not cause the flow of acid to stop over time (see the first case above).

Increasing the concentrations will increase the rate of CO2 production to a certain point that the pressure on the soda bottle will be higher than that of the acid bottle. At this stage, gas will flow back to the acid bottle to equalize the pressure differential. This equalization is not instantaneous as the solution has to flow back through the tubing. The length of this tube adds to how big the pressure fluctuation is.

Higher concentrations will tend to create higher internal pressures but it will never cause the pressure to continuously buildup.

The effects of leakage for either bottles will still be the same as in the previous setup.

Note that the above explanation assumes that the needle valve is a regulator. In reality it is just a flow restrictor that depends on the pressure difference between the input and output ports. This is the reason why we sometimes need to adjust it whenever the pressure inside the system increases or decreases over time.

Sorry for the long post, I hope my explanation is clear.

Please don't go back to the yeast setup, fix the leaks and you'll be ok!

 

[Hoppy]

Sorry for the long post, I hope my explanation is clear.

Please don't go back to the yeast setup, fix the leaks and you'll be ok!

Your explanation is clear, but I think it undervalues the effect the CO2 production has on the process. Adding a drop of acid in the soda bottle causes the solution to start producing CO2, but that production takes many seconds, even a minute or more, to play out. During that time, if the needle valve is closed, the CO2 builds up pressure in the soda bottle, which forces CO2 to go back up the acid supply tube to the acid bottle to equalize the pressure again. As long as the CO2 is still being generated that CO2 flow back to the acid bottle continues. Opening the needle valve releases some CO2 from the soda bottle, reducing the pressure, but the CO2 production is still continuing, so the pressure may not reduce enough or long enough to again allow acid to flow into the soda bottle. So, there is a slow motion tug of war between the produced CO2 and the acid trying to flow into the soda bottle. I think this makes the process much more complicated than it seems it would be.

After I get a squirt of acid into the soda bottle it takes minutes for the resulting club soda-like solution to stop bubbling - producing CO2. This is making me wonder if the acid solution strength isn't more important than I have assumed.

I haven't restarted my CO2 system yet this morning. When I do I will see if there is something else interesting to report.

EDIT: When I checked the system this morning it had 5 psi in it, down from 10 psi last night. There was just a little baking soda left in the soda bottle. I shook it, squeezed some acid into the soda bottle, and opened the needle valve to a high bubble rate. After about an hour it was producing no CO2, and when I checked the soda bottle again, there was no more soda in it. So, my 100 ml of baking soda lasted 6 days. About half or more of the acid is still there. When I restart this I will use 200 ml of soda, and hope that stretches out the production for 10 days or more. It looks to me like the soda water is saturated with soda, and as it gets "used" up more dissolves, and when there is no more left to dissolve there is only an hour or less of CO2 production left. This, at a 5 or more bbs production rate. Perhaps if I diluted the acid more, I could get a longer production at a stable 1-2 bbs rate.

 

[kinsa]

...

EDIT: When I checked the system this morning it had 5 psi in it, down from 10 psi last night. There was just a little baking soda left in the soda bottle. I shook it, squeezed some acid into the soda bottle, and opened the needle valve to a high bubble rate. After about an hour it was producing no CO2, and when I checked the soda bottle again, there was no more soda in it. So, my 100 ml of baking soda lasted 6 days. About half or more of the acid is still there. When I restart this I will use 200 ml of soda, and hope that stretches out the production for 10 days or more. It looks to me like the soda water is saturated with soda, and as it gets "used" up more dissolves, and when there is no more left to dissolve there is only an hour or less of CO2 production left. This, at a 5 or more bbs production rate. Perhaps if I diluted the acid more, I could get a longer production at a stable 1-2 bbs rate.

The 5 psi drop in your acid bottle is not supposed to happen if there are no leaks in the system. Especially if the valve is closed.

According to this guy, the amount of soda that you're using is half of what it is supposed to be. Please use a scale if you happen to have one.

I'm running my setup at 1 bubble every 4 secs and according to the manufacturer it is supposed to last close to 80 days. It is now at 51 days and my acid level hasn't dropped to 3/4ths yet.

So 16 days @ 1 bps should not be a problem.

 

[Hoppy]

I restarted my CO2 system this afternoon, after 2 days off due to life interfering. Again, I just don't have the hand strength to build up a 15 psi pressure in the bottles. Five psi was my limit today. It is now running about 2 bbs and is relatively stable. When I refilled the bottles, I added another 600 ml of acid solution to the approximately 200 ml still there. And, I used double the soda to about 200 ml in about 200 ml of water. I can't see any difference in how it is working.

The reason I don't weigh the powders is that I don't see any reason to do so. The density of citric acid powder and baking soda are pretty well known, and there is no technical reason I can see for precision in measuring them. Plus, my gram scale is stashed somewhere where I haven't found it!

 

[jrill]

I restarted my CO2 system this afternoon, after 2 days off due to life interfering. Again, I just don't have the hand strength to build up a 15 psi pressure in the bottles. Five psi was my limit today. It is now running about 2 bbs and is relatively stable. When I refilled the bottles, I added another 600 ml of acid solution to the approximately 200 ml still there. And, I used double the soda to about 200 ml in about 200 ml of water. I can't see any difference in how it is working.

The reason I don't weigh the powders is that I don't see any reason to do so. The density of citric acid powder and baking soda are pretty well known, and there is no technical reason I can see for precision in measuring them. Plus, my gram scale is stashed somewhere where I haven't found it!

Keep us posted. I plan to use your formula tomorrow to see if results vary. Was going to do that last Friday, but like you stuff got in the way.

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[jrill]

Hoppy, started mine up about an hour ago using your formula at 1bps. So far there has not been a move of citric acid since start up.

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[Hoppy]

Hoppy, started mine up about an hour ago using your formula at 1bps. So far there has not been a move of citric acid since start up.

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Is this different from what you normally see? Have you, by any chance, measured the volume of a specific weight of citric acid powder? I used the published density to figure out the volume I used.

 

[jrill]

Is this different from what you normally see? Have you, by any chance, measured the volume of a specific weight of citric acid powder? I used the published density to figure out the volume I used.

So far it's normal from what I usually see. I have not measured weight to volume. I can't today but I will tomorrow.

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[jrill]

Ran normally till the solenoid shut it down at 8.

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[Hoppy]

If I had a leak in the tube going from the acid bottle to the soda bottle, located inside the soda bottle, would that affect the operation? I ask because my bottle caps are the Ebay ones, where the tube doesn't go through the cap. Instead it attaches with a fitting that crimps itself onto the tube when you screw down the fitting nut, on on the inside the tube just slips over a stub of plastic. I can't see a problem there, but I may be overlooking something.

My bottle pressure still slowly drops during the day. If a leak at the cap causes the system to be unable to easily move acid to the soda bottle, that could be a problem.

 

[jrill]

Is this different from what you normally see? Have you, by any chance, measured the volume of a specific weight of citric acid powder? I used the published density to figure out the volume I used.

Good morning. Measured volume.
Citric acid volume of 250ml weighed 249g.
Baking soda 100ml is 133g.

My system held pressure over night and should start just fine later. I would double the baking soda if going by volume to 200ml or so. The amount of baking soda present from the 100ml is about what I would see after a few weeks of operation.
Not sure what to make of a possible leak inside your soda bottle, but it seems certain that your system is doing something different than mine.

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[Hoppy]

Thank you for the density data! The citric acid is far less dense than the published data on it. It should be about 1.6+ gram per ml, vs your 1.0 gram per ml. So, I may have far less citric acid than I probably should have. Baking soda should be 2.16 gram per ml, and you got about 1.33 gram per ml. But, I'm suspicious: both of your measures were about .62 of what they should be. Perhaps the published numbers are based on firmly packed volumes?

 

[kinsa]

If there are bubbles inside the hose going to the soda bottle then you have a leak on the hose inside the acid bottle.

 

[jrill]

If there are bubbles inside the hose going to the soda bottle then you have a leak on the hose inside the acid bottle.

I'm not sure that's true. I have the solid bar set up instead of the hose but when the acid pumps over its not a solid stream.

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[Hoppy]

That hose into/out of the acid bottle alternates between allowing pressurized CO2 into the acid bottle and acid back into the soda bottle. I suspect it will always have a few bubbles in it. The only time it wouldn't have CO2 going to the acid bottle is if it is stable, and holds its pressure, but as acid leaves the acid bottle the pressure in that bottle has to drop, so to keep the system working CO2 has to get back to replace the lost acid. I still can't get a mental picture of just how this thing goes about doing its job. It seems like it needs a separate CO2 tube to the acid bottle, and an acid tube to the soda bottle, with check valves so both can only allow passage in one direction.

 

[kinsa]

...
I still can't get a mental picture of just how this thing goes about doing its job. It seems like it needs a separate CO2 tube to the acid bottle, and an acid tube to the soda bottle, with check valves so both can only allow passage in one direction.

What you've described is the complex version: http://www.plantedtank.net/forums/20-diy/188249-co2-generator-yuri-tpv.html The tee fitting is the simplification of the two check valves.

Once the pressures have reached equilibrium, the acid flow goes only one way. It only backs out briefly after it mixes with the soda solution but no new bubbles are introduced back into the acid bottle. The maximum pressure that the newly generated CO2 creates is less than or equal to the pressure inside the acid bottle when the system is at equilibrium.

 

[jrill]

What you've described is the complex version: http://www.plantedtank.net/forums/20-diy/188249-co2-generator-yuri-tpv.html The tee fitting is the simplification of the two check valves.

Once the pressures have reached equilibrium, the acid flow goes only one way. It only backs out briefly after it mixes with the soda solution but no new bubbles are introduced back into the acid bottle. .

I respectfully disagree. After using the System for over a year I see bubbles going over to the acid bottle many times over the exchange of pressure.


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[Hoppy]

JACKPOT! That answers all of my questions, and offers some ways to make the system be more stable - I think. Best of all, it is a treasure trove of experiments to try, and how can you beat that? This may be Russia's best contribution since Tchaikovsky!

 

[kinsa]

I respectfully disagree. After using the System for over a year I see bubbles going over to the acid bottle many times over the exchange of pressure.

Mine doesn't. It's the reason why my setup hasn't breached the 3/4 level after almost 2 months now (54 days to be exact). At this rate, 6 months looks doable