# venturi loop for in-line CO2 reactors



## Rob G (Oct 19, 2004)

A while back in another thread, plantbrain posted the following:

Quote:
Originally Posted by plantbrain
I designed my internal reactors to prurge the excess CO2/O2 for this reason. I am working on a DIY external that addresses this as well. 


To which I replied:

"Tom, can you provide some insight as to how you think this can be addressed. I've been thinking about how a venturi loop could be added to an in-line, external reactor, but I've yet to come up with a good solution.

Does anyone else have any ideas?"

A recent post related to Gomer's CO2 reactor thread (sticky), in which "burping" reactors was mentioned, reminded me of this topic. So, does anyone have a design that expels the built-up gas in a reactor plumbed in-line with a canister filter's outflow? Is our only hope to invert the reactor occasionally?


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## gnatster (Mar 6, 2004)

Happens that Niko and I were discussing this very thing when taking a good look at an AquaMedic 1000. The 100 has a bleed port (for lack of a better term) on top controlled with a small valve.

In the image below the bleed is in the back and has a length of now semi clear airline on it, the valve is in the open position. My original intent was only to extend the bleed line as it was not in a handy position and that is still how it is used, an airline valve was placed on the end in a more handy position.










The discussion went along the lines of leaving it permanently open and teeing the bleed line to the reactor intake line. Given further thought the bleed line should also have a tee, the leg extending out to another valve to facilitate a bleed as needed, such as after a cleaning. The addition of a check valve after the bleed off Tee would prevent water from backing up during the bleed.

I tried to draw an example below, an artist I am not.


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## Rob G (Oct 19, 2004)

gnatster, I like where you are going with this. I have a couple of follow-up questions.

First, in your existing set-up, when you open the bleed line valve, what prevents water from exiting the bleed line? I would think that the tendency would be for water to be forced out of the bleed line. Then again, maybe that is the way it is supposed to work - the water pressure forcing the air out. Do you have to quickly close the valve to prevent water from exiting the bleed line?

Second, how do you propose the bleed line be attached to the main tube flowing into the reactor? I was thinking that with a DIY reactor, a piece of 1/4" or 1/2" PVC approximately four inches long could be placed on the inflow of the reactor, just behind a barb used to attach it to the flexible hosing. This PVC extension could be used as a place to attach the "venturi loop" from the bleed line. I'm not sure how long the PVC extension would need to be, but I would think that the bleed line would need to be attached far enough above the body of the reactor to ensure it is in a high-flow area (i.e. smaller diameter than the reactor) in order to generate a sufficient draw on the bleed line. What do you think?


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## gnatster (Mar 6, 2004)

> First, in your existing set-up, when you open the bleed line valve, what prevents water from exiting the bleed line? I would think that the tendency would be for water to be forced out of the bleed line. Then again, maybe that is the way it is supposed to work - the water pressure forcing the air out. Do you have to quickly close the valve to prevent water from exiting the bleed line?


When the bleed line is opened pressure does force any residuial air out of the reactor followed by water. I extended my bleed line to be over the sump, so when the water comes rushing along it flows back into the sump. For the sumpless, just hold it over a cup.



> Second, how do you propose the bleed line be attached to the main tube flowing into the reactor? I was thinking that with a DIY reactor, a piece of 1/4" or 1/2" PVC approximately four inches long could be placed on the inflow of the reactor, just behind a barb used to attach it to the flexible hosing. This PVC extension could be used as a place to attach the "venturi loop" from the bleed line. I'm not sure how long the PVC extension would need to be, but I would think that the bleed line would need to be attached far enough above the body of the reactor to ensure it is in a high-flow area (i.e. smaller diameter than the reactor) in order to generate a sufficient draw on the bleed line. What do you think?


At the highest point I would place a fitting like that found here 
Then an adaptor T to splice into the reactor intake.


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## Rob G (Oct 19, 2004)

gnatster said:


> At the highest point I would place a fitting like that found here
> Then an adaptor T to splice into the reactor intake.


Funny you mention the Fourmost fittings. I actually have a few left over from my DIY yeast reactors. I have the exact fittings pictured in the link you provided, and I found them to be a wee bit too small to provide a secure grip on standard 1/8" air tubing. They do make a slightly larger fitting (I think they are blue and yellow). I have since had better luck just drilling a hole (I think 3/8", but I don't have my drill bits with me) slightly smaller than the air tubing, cutting the tubing at an angle, and pulling it through the wall where a bulk head fitting would have been used with a pair of needle nose pliers (thanks to Rex Grigg for that tip). This forms a very tight seal. That's how I am injecting my pressurized CO2 into reactors these days.

Thanks again for the great idea. I think I will try to create something like this in the near future. When I do I'll be sure to post pictures and report back on the success or failure of the venturi effect.


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## Rob G (Oct 19, 2004)

I may have just thought of a slight problem with the position of the venturi loop in the above drawing. It is my understanding that the spliced bleed line was going to be diverted back above the inflow of the reactor (top). I am now not sure that this would result in the desired effect. If the excess gas (oxygen and nitrogen?) is pulled back to the inflow, it is just going to end up back in the reactor. 

I think the design might need to be adjusted to divert the bleed line to the outflow (bottom) side of the reactor. Then, the excess gas would be expelled through the spray bar or whatever else is at the end of the line. I think this would work as long as the CO2 is injected somewhere near the middle to bottom of the reactor. If the CO2 is injected at the top, this venturi loop might just cause the CO2 to bypass the reactor. 

Can anyone see a reason why connecting the bleed line at the top of the reactor to a point after the outflow of the reactor would not work or might cause problems?


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## gnatster (Mar 6, 2004)

My thoughts were to bring the CO2 back in to fully dissolve, not to expel it out the spray bar. One caveat, these are just thoughts of how it would work, Have not created the venturi in my setup as of yet but now I am looking at constructing one just to try it out. The thing is, I have not had any issues with gas not getting dissolved in the reactor and I pump in a lot of CO2.


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## Rob G (Oct 19, 2004)

I agree, I wouldn't want to expel the CO2. I haven't had any issues with CO2 not dissolving (my reactor is overkill at three feet long), but I do get the occasional accumulation of what I believe to be other gases at the top of the reactor after opening my cannister filter for cleaning. 

Your existing bleed line without a venturi loop would solve my problem, but I thought it would be nice to have the process automated so as not to require one to open a valve in the event of a non-CO2 gas build-up. Yet, I am beginning to think that a simple bleed line will solve the problem with less effort. What type of airline valve do you use at the end of your bleed line?

I do, however, think that your venturi loop design as pictured in the drawing, is a great idea if someone had limited cabinet space and needed a short reactor chamber combined with a high flow rate. Maybe that was why you and Niko were discussing this. If memory serves me correctly, his latest reactor design was an effort to enable a very high flow rate. 

If you do end up implementing a venturi loop, I'd like to see photos. Thanks again for the help.

Rob


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## gnatster (Mar 6, 2004)

> What type of airline valve do you use at the end of your bleed line?


Plain old airline tubing, valve is one of those found in your basic airline tubing accessory blister pack.


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