# venturi effect



## predator (Jan 28, 2005)

ok guys I'm still in the planning stage of my sump setup and i was wondering if anyone had ever used the venturi effect to pull water from the fuge into the return line... If so what needs to be done to insure that it will work?

for those not familiar with this effect it is simply if you pass a fluid past a perpendicular (90 degree) pipe it will cause a vacuum pull fluids from the other pipe...

-me


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## TheOldSalt (Jan 28, 2005)

I can't think of that ever being done right off the bat, but why on earth would you ever want to do it that way?


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## predator (Jan 28, 2005)

Ok so here goes... pretty simple... water comes down and enters sump (via overflow in tank)... gets heated, skimmed, tested, and what ever else you want... from there it is pumped back up to the tank... As it it pumped past the line comming from the fuge it draws a vacuum on that tube and pulls water from the fuge and takes it to the tank... This drops the level in the fuge and the syphen into the sump fills the fuge again...

y woudl you want to do this? notice... 1 pump... with out having to have your fuge stacked on ur sump... also the fuge water never passes through a pump... so none of your critters get chewed up...

Mainly... 1 pump... and its cool...

-me


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## TheOldSalt (Jan 28, 2005)

Okay, that is pretty cool.
It's gonna be one royal pain* every time the power goes out, but until then it would rock.

*- How are you going to prime it?


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## predator (Jan 28, 2005)

ok so y is it going to be a pain if i loose power?

and prime it? expain what you think needs primed?

-me

p.s. My reply box is like 3 inches wide.... WTF? is anyone elses?... Im like typing a frigging column here....


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## CollegeReefer (Sep 1, 2006)

I really need to post pics of what i did so you can seen something a little easier and reliable.


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## TheOldSalt (Jan 28, 2005)

You don't see the problem in your picture?

What happens when the power fails? The water in the outcurrent tube falls. Air gets into the venturi line, breaking the flow. It might restart upon repower, but it might not. It probably will if the end in the fuge stays submerged, and if it's not too steep a climb.

Another possible problem is that the water in the sump will also pull on the u-tube as the pump draws it, and possibly strongly enough to retard flow into the fuge half. This could result in a fuge that drains out faster than it gets refilled. More u-tubes might fix this.


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## predator (Jan 28, 2005)

Ok i see your concerns... here are my questions to you though... if my nozzle in the display tank is under water (which most are) and i loose power the water will flow backward and flood my sump... this can be stoped 2 ways... a lil hole somewhere over the water line... or a check vavle...

if a check valve were installed to solve this there would never be air that made it into the fuge line... and even if it did i would just think it would reprime itself (time would tell i suppose)...

now to the u tube issue... ohhh ok i get you your saying the u tube being that close to the pump might cause and issue... that was simply placement in the sketch... i wouldnt get the u tube that close...

-me


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## TheOldSalt (Jan 28, 2005)

A check valve would fix the first problem, no problem.

The second problem isn't one of proximity to the pump. It's one of the sump water flowing out faster than the fuge water flows out, resulting in the u-tube trying to run backwards.


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## predator (Jan 28, 2005)

Ok so im back to not completely understading this one again...

i have 110 GPH going out (estimate)...100 is from the sump and 10 is from the fuge... so 110 gph is comming frome the display tank... to regulate the level of the tanks the 10 gallons you pulled out is going to have to re-enter the fuge... i dont guess i know how ther would ever be revers flow?

maybe you can expalin a bit better...


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## TheOldSalt (Jan 28, 2005)

Who says you'll have everything work out so neatly that 100 gals comes out of your sump while 10 comes out of your fuge?

Even if that did happen, you have a 10-to-1 ratio of sump flow vs 'fuge flow. That sounds fine until you consider that the u-tubes are going to HAVE to deliver exactly that 10 gallons to the 'fuge to keep it level. It should do just that, BUT:

The directional flow in the u-tubes will be dictated by whichever side is pulling on it the hardest, and which path offers the least resistance. In your drawing, the bigger, lower u-tube gives the 'fuge water a much easier place to go than up that venturi tube.

You could well wind up with TWO tubes trying to pull water out of the 'fuge at worst, or at least be aggravated by a slowly dropping waterlevel in the 'fuge because the u-tube can't keep up.

Or maybe it'll work just fine. Hydraulics are funny that way. I wouldn't bet on it, though.


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## jones57742 (Sep 8, 2007)

predator said:


> for those not familiar with this effect it is simply if you pass a fluid past a perpendicular (90 degree) pipe it will cause a vacuum pull fluids from the other pipe...


predator and folks: Please excuse me here but pred's statement is substantially incorrect.

Per predator "perpendicular pipe" the velocity of the medium must be such that the kinetic energy is greater than than the potential energy.

Torricelli's equation* is the very simplistic equalization of potential energy to kinetic energy in non real world environment.

Bernoulli's equation is the general form of energy transformation from potential to kinetic in the real world although this equation does not set forth specific heat losses.

For all the folks out there who have given me grief please google for the words and my assertions will become intuitively obvious.

TR

*
mgh = potential energy
1/2(mv^2) = kinetic energy


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## predator (Jan 28, 2005)

There you go...

http://en.wikipedia.org/wiki/Venturi_effect

and yes im aware that you have to have a increase in velocity to cause a vacuum... and im familiar with the Bernoulli's equation... I know i put it very bluntly and overly simplified... I was more asking about the theory than the mechanics... I have not formulated anything and dont know if it will pull enough vacuum or not which such a low flow rate (without causing such a restriction that my pump will over load)... I should not have stated it as simply as i did..

If you want to get into the formulation with me and talk about that I would gladly like to have a second brain looking at this with me...

And TOS... Our brain waves just arent meshing... if these tanks are on the same level i do not see how the water level could be more than just a few fractions of an inch different.... and if you are pulling out with one tube... your gonna have to have water comming in the other tube...

im prolly just gonna go buy some tanks and start getting into test mode...

-me


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## jones57742 (Sep 8, 2007)

predator said:


> If you want to get into the formulation with me and talk about that I would gladly like to have a second brain looking at this with me...


Absolutely!!!!

Your notes would be a ton of help with my experience without my experience being hard earned.



predator said:


> im prolly just gonna go buy some tanks and start getting into test mode...


Once again the publication of your notes will be first class.

TR

predator:

I was not and am not talking down but if you believe that you do not understand the Newtonian (classical) concept of conservation of energy (ie. energy is energy whether the energy be kinematic, potential, heat, etc) please advise as this understanding may save you a ton of grief.

BTW: you would not believe the percent of Registered Engineers who do not understand the concepts which we are discussing (is this not a sad state of affairs?).


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## CollegeReefer (Sep 1, 2006)

Alright Here is a pic of what I did and i think it is really affective.

First off i have my sump split into three sections. Left side is where the protein skimmer is, center is my return pump, and the right side is my refugium. Water is split using a T between the right and lift side. I then have a mj that pumps water from the refugium to my frag tank. You can see the pvc tubing used in the front right of the tank. I use a u-tube to bring the water back from the frag tank to the refugium. In the rufugium i use a pvc with cap that acts as the prefilter. This also keeps the water at a constant level. I hope this makes sense.










The back left of the frag tank you can see the 2 inch pvc.









I hope this helps a little. I considered directing the water from the display to go into the frag tank instead of the fuge side of the sump but if i did this i would have a lot of air bubbles in the frag tank and decided to use the pump instead.


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