Aquaponics - Venturi

A venturi is a lot of things, but in an aquaponics system it's a noun, and refers to a way to introduce lots of air bubbles into a stream of water.

It tuns out, if you have an elbow in a pipe, or some other temporary restriction, the water is under increased pressure before the restriction, and at a lower pressure immediately after the restriction.

The odd thing about that, is that its useful.

Who would have thought.


If you have a restriction in a pipe and you prick a hole just before restriction (between the pump and the restriction) you get a leak in your pipe. We hate leaks, so don't do it.

But if you prick a hole in the pipe just after the restriction (between the restriction and the fish tank) you get a venturi. Actually you probably get something called a venturi effect air tube or something.

But what you really get a venturi.

As the water gets near the restriction, it slows down and as result, there is a pressure localised pressure increase. When it passes through the restriction and opens back up to the normal pipe size, it is allowed to speed back up, and as a result finds it self at lower pressure.

I think.

If there is a hole in the pipe where the pipe is at higher pressure, the water looks to escape, and does so through the hole. If there is a hole in the pipe where there is a lower pressure, the water is quite content to be in the tube, because like everyone else, if your situation is getting slightly easer to move around, and you are under slightly less pressure than you were a while ago, you become content.

The result of a low pressure area with content water is that it sucks in air instead of spitting out water.

This can be a good thing if you are trying to put air into your water, or break up the surface tension on the top of your fish tank, or trying to make one of those low flow shower heads that don't quite wet you as well as just dumping a stack of water on your head.


But dont take my word for it.

I'll build one.

I have a pipe flowing water into my new IBC fish tank.

Try not to notice the massive algal bloom that's occurred as a result of there being too much nutrient in Adelaide water, and the tank just sitting for a week or so.

That's water, not a sports drink.

When you submerge the end, it looks like this.

Interesting, isn't it.

Next we prick a small hole in the tube about halfway along its length.

I was looking for something like a nail to prick a hole in my hose, and found this instead.

I just worked out what it's for. I've had it for ages.

One end has a point for putting holes in black poly pipe, and the other end has a hex spanner for  screwing in the little connectors that have a point on them for things like dripper systems, and little sprinklers etc.

So far in my life, on the odd occasion when I've done such gardening stuff, I've been just forcing the connector things through after making a hole with a nail.

This tool thing works really well.

Anyway...

I turned off the water flow and made a hole.

Interestingly (this isn't the interesting bit) the water dribbled out a bit...












and... (<= that's the interesting bit)

also made a few bubbles exit the pipe under water.

When I created a restriction in the pipe below the hole we see increased pressure as the water piles up at the restriction, and distinctly more water exited through the hole. The photo didn't really capture it, but it was probably 5 times more water.

We also see no air exiting the tube at all.

But when I create the restriction before the hole, we see no water flow out of the hole at all.

And a stack of bubbles exiting the pipe under water.












There, except for any errors I've made, that's probably all you will ever need to know about a venturi.





This 120 Things in 20 years post, looked like something on the venturi effect in an aquaponics environment, but I think in the future's history, it will prove prove to be part of something more to do with the Murray river and the environment.