Understanding venturi

devocole

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Mar 17, 2008
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I'm about 3 months new to the planted tank hobby and have decided to construct or buy an external reactor for my CO2 system. But one term keeps coming up and i just don't understand it: "VENTURI" I've been reading wikipedia etc and just can't grasp the concept. I was hoping someone could give me an explanation on its meaning so i can understand all the talk involved in the DIY double venturi reactor system.
Thankyou
Devon
 

Mooner

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A venturi can also be used to mix a fluid with air. If a pump forces the fluid through a tube connected to a system consisting of a venturi to increase the water speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), air will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of fluid and air will appear. (Venturi effect - Wikipedia, the free encyclopedia)

As far as the dual venturi external reactor, It is two points at which CO2 can be injected and/or recirculated. I have built 2 so far with mixed results. Don't get me wrong, they do work well but still working on the recirculation or in my case the lack of. My best results so far have been to not use either venturi and feed CO2 directly in to the power head pump. Still have substantial gas buildup in the reactor by the end of day but this has no effect on the tank or the ability to maintain good CO2 levels.

So good luck when you build one, you may also consider a power head only in the tank with modified impeller and CO2 connected directly.
 

devocole

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Mar 17, 2008
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Okay, that helps a bit. So in the dual venturi. The tube in the top with the ball valve, if you open that up, air will get sucked into the system and "purge" the co2 and everything else out? The tube on the side of the reactor that is connected back to the rio pump, that will carry any extra CO2 back into the rio right, but if there isn't any CO2 build up, it will just be water from in the reactor right? Do i understand what the 2 venturi points are for? Also i don't what to have the pump in the water, i'm going for very little hardwear in the water, is it possible to do this with a pump that has a tube in the tank that connects to the pump, and then forces the water through the reactor.
I'm coming along slowly.
Thanks
 

tedr108

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Devocole,

I got a little confused about "venturi" also when I got into this hobby and built my external DIY reactor, so I hear you. Although there are 2 possible locations with this design to put your venturi loops in the reactor, you only use one of them. I believe that most people just use the one on the side and use the top tube as a bleeder valve to allow the bleeding off of air/CO2 collected at the top of the reactor.

Personally, I did not like the side tube and put 2 venturi tubes in the top ... one to feed the accumulated CO2 back into the pump and one to bleed with, which allows my reactor to fill completely with water very quickly.

Very simply, here is what your venturi loop will do for you: As CO2 dissolution slows down after a while, CO2 will often accumulate at the top of the reactor. When the level of CO2 accumulates to the level of your venturi loop, the venturi kicks in. The suction from the pump ("venturi") pulls the CO2 in and the pump impeller chops the CO2 into very small bubbles. The little bubbles do not rise like big bubbles in the reactor, they flow thru with the water and come out of your output nozzle as a fine mist.

This reactor surely would work with an inline pump as you are asking. Many folks simply put it inline with one of their canister filter's lines -- the output, I believe. You can still do the venturi loop with this method. If you decide to try the inline method, many here will be able to give you some good advice.
 

Mooner

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Ted,

Are you using both an external reactor and modified impeller power head??

Also do you have issues with the recirculation in the external reactor once the gas builds up? I recently upgraded from the Rio600+ to the Rio800+ and still experienced lockup(only 10gph more:( ). Next to try will be the 1000 for the external reactor.
 

tedr108

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Hi Chris,

No, I shut down the external reactor a while back -- it worked very well, however. I'm simply using the powerhead now, and it is working very well for me also, perhaps even better than the external reactor. I even took out the modified impeller and put in a regular one, and changed the technique a little -- my powerhead is definitely moving some water around. Most of my CO2 is now completely dissolving and even in the afternoon my bubbles are so small that I cannot even see them unless I stick my nose right up to the glass. I'm getting a nice light green drop checker.

Here’s a recent thread I posted, which you may have already read:
http://www.barrreport.com/co2-aquatic-plant-fertilization/4118-co2-distribution-w-powerhead.html

I think I mentioned to you before that the Rio 800+ was borderline for me also. However, I only had a problem at startup after a water change, when the reactor had drained out quite a bit. My little 800 often couldn't quite get the reactor full and really struggled like yours (mine was also noisy during this time). That's when I put the extra bleeder valve in. Once my reactor was full and running, however, I never had any issues after that. I'm wondering how much extra tubing you are making the powerhead pump thru. I kept mine at a minimum.

I'm sure that the 1000 would make a difference. I never upgraded to the 1000 since I like the results of the powerhead CO2 experiments -- simple, effective and much more quiet that my external reactor.
 

Mooner

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tedr108;24104 said:
I'm wondering how much extra tubing you are making the powerhead pump thru. I kept mine at a minimum.

Interesting thought, Here's what mine is.
Standard external reactor per article. 1" deep bleeder on top, 12" drop for CO2 in, 2" long piece 2" down in side wall.
Modifications: 1/2" tubing in from power head(per article) 3/4" bottom of reactor to tank.

Now for your question on tubing length. Bottom of reactor to tank is 2.5ft x 3/4"to get output to other side of tank(30 gal) maybe this is where a bigger pump might be needed?

For a short while I tried the modified power head but didn't like the snow globe effect, though no problem getting CO2 levels up fast. This was the 600+ with modified impeller and CO2 in venturi port. Maybe I will try again with a standard power head similar to yours on a different tank to observe differences.
 

devocole

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Mar 17, 2008
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Thanks alot for replying Ted. The external reactor sounds like a bit of trial and error, but definately gets the job done. I want to go for simple and effective, so the powerhead idea sounds interesting. But i want my system to be external so a reactor might be the right way to go.

Now about the venturi talk. I'm getting better but you may have to dumb it down even more for me. Water pressure etc in physics class wasn't my strongest subject. Now if i were to do this with and external pump. I would have a tube from the pump in the tank, and a tube going into the reactor. So input into the pump, and output into the reactor. Now where does that venturi tube a ma bob get put back into the pump? Is it to the inline tube into the pump? I'm still confused.

Thanks again
 

tedr108

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Since I've never done the external reactor with an inline pump, I'm hoping someone else will pipe in here. I've never even seen an inline pump to be honest. If there is an inline pump with a venture inlet, you are set ... you would just run the venturi loop from the side or top of the external reactor to it. Now, if you have to make your own venturi inlet, I'm thinking you would put it on the intake side of the pump somehow ... in the tubing probably. That would surely create enough suction to create some venturi action (suction). That seems a little tricky to me, as far as tubing goes, you may need to use a little PVC pipe. The rigid 3/16" tubing fits very snug into a 3/16" hole and you could use a little PVC cement to seal the rigid tubing into the PVC to be your venturi nipple.

If you get no more responses to this thread, make another thread asking your specific question of how to do the external reactor with an inline pump and how to put a venturi loop into it.
 

tedr108

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Chris,

My reactor was pretty much spec except for no side venturi. Sounds like you have an extra foot of tubing or so. Also, I only used 1/2" tubing all the way, even out of the reactor. Since my 800 was seemingly borderline, perhaps this is enough extra tubing that you are having problems.
 

devocole

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Mar 17, 2008
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Okay i think i've grasped it. Its taken about 5 hours but i think i get it. I'm going to start a new thread to lay out my options, and confirm that my understanding is correct.
Thanks
Ted