Question about Venturi


brandonsdad02

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I've been thinking about building a venturi for my pond set up right at the top of the down pipe for my skippy. I have 2 plants in there now and thought the added O2 wouldn't hurt. My question is.....Would it help? Where the water level is in my skippy and the top of my down tube going to the swirl bars is about a foot of distance that the water flows before it gets to the water level in the skippy. I get tons of bubbles in my skippy that come up from the bottom on each side. And next how would I add this to my current set up? My hose comes from the pump to the down tube in the center of my skippy. Its flexable hose.
 
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koiguy1969

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a real venturi would infuse more air than what your backflow "syphon break" does...thats the reason the wastes tee is used on top of the downpipe. it breaks the syphon affect should your pump ever quit or get turned off. it keeps the filter from syphoning back into the pond. it wouldnt be a hard job to install a cap on top of the down pipe and drill lt to accept a venturi...
 

brandonsdad02

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I tried a plumbing wye where I put the fitting on top of the down tube, put the hose coming in the curved opening and the air tube coming in on the top, but it didn't work very well. What exactly will I need to make a venturi
 
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I tried a plumbing wye where I put the fitting on top of the down tube, put the hose coming in the curved opening and the air tube coming in on the top, but it didn't work very well. What exactly will I need to make a venturi
I didn't follow that exactly but the classic method would be a horizontal pipe under the water with a pump pushing water through the pipe. Then a tee is added and a vertical pipe to above the water surface. As the pumped water goes by the pipe to the surface air is drawn down into the water flow and air bubbles come out the pipe with the water.

It probably wouldn't add much, if any, O2 to your pond. O2 is added to the pond at the surface. Air pumps work by moving water to the surface where gas exchange can happen. It just happens that an air pump is more efficient at moving water to the surface than a water pump, the bubbles move water, not add O2.

Depending on placement the bubbles from a Venturi could in theory increase water movement a little. But the pump is moving most of the water. You can maximize this by sending water from the Skippy to the pond bottom to try and set up a current to mix the pond as much as possible. In most water gardens this isn't needed.

If you do want more O2 you can't beat an air pump.
 

brandonsdad02

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I have a air pump hooked up now but I can't really see how much better it is compared to a waterfall. You still get the same result, O2 in the water which is what we want. The waterfall breaks the surface of the water which then forces O2 in the water and the force of the water coming down makes it go underwater and the bubbles come up to pop. Same thing a air pump does, just not contained to a tube and going thru a air stone.

Please explain this or are they the same?
 
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You have it right. The advantage of the air pump is purely a that it cost less to run. The down side is zero head.

A bit more specific on how O2 gets into the water...doesn't really have anything to do with breaking the surface exactly. There have been some studies on surface tension and gas exchange. Lowering the surface tension did increase gas exchange but not a lot. And they broke surface tension with chemicals. A waterfall doesn't effect surface tension that much. It streams and falls do increase surface area and of course movement.

In a perfectly still body of water there would only be gas exchange at the very surface, like the top 1/32". But that thin layer would always have as much O2 as it could. Below that it drops off to almost nothing. So life below the water would use O2 up pretty fast and die. In real life of course there's no such thing as "perfectly still". Wind, thermal currents, fish swimming all provide enough movement that water gets a chance to be at the surface, exchange gases and keep moving. Add a pump to that and you have even more.

Large fish need more O2. So in a Koi pond full of large fish a huge amount of water movement is needed to keep O2 levels high enough to keep fish alive. In water gardens generally even a pump isn't actually needed. Although of course the fish would rather have the extra O2.

Gas exchange happens the same way in water as in air and between the two. Gas in an enclosed container will spread out very fast until the modules are all basically the same amounts apart. Just a lot slower moving through water.
 
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