A Venturi creates a low pressure by the flow of a fluid speeding up in a cone-like constriction. As the fluid exits the constriction, the flow is reduced and the pressure is increased once more.
What is a Venturi Aerator?
A venturi aerator increases the amount of dissolved oxygen in the water. This is done by use of the Bernoulli principle whereby air is sucked into a high-velocity area of a pipe and injected into the water stream.
Traditionally, the oxygen in a fish tank is added by the use of an air pump and air stones which increases the operating costs by using electricity. A venturi uses a steady flow from a water pump’s outlet to inject air into the water entering the fish tank.
Water aeration occurs when air is sucked in at the restriction of a venturi and enters the water stream as bubbles, increasing the dissolved oxygen as the water exits the Venturi.
Oxygen is not supplied directly to the water by the bubbles, instead, it’s the actual agitation of the water which causes the oxygen to be dissolved.
How does a Venturi Work?
Before we dive into making a Venturi let’s learn a bit of science about what causes a venturi to suck in air from the outside.
Drawing Showing the Venturi Effect
The Bernoulli principle –
Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid’s potential energy.
P1 + V1 = P2 + V2
The pressure, P1 is greater than P2
The water’s velocity, V2 is greater than V1
What this simply means is that the water pressure (P1), before the reduction is greater than the water pressure (P2) at the reduction.
This results in the water velocity (V2), being greater than the water velocity (V1).
The reduction in pipe size causes the water to speed up resulting in a pressure to drop at that point, pulling air into the pipe from the outside.
Once the air is sucked into the water stream it is carried into the fish tank as tiny bubbles which causes agitation. This agitation in turn helps oxygen to be dissolved into the water. The oxygen is then used by both fishes and plants to carry out their daily functions.
I found that this Venturi Aerator from amazon is durable and of excellent value for money. You can find it by clicking here.
How do you make a venturi?
Making a venturi is simple and can be done using only pieces of PVC pipes
The basic principle we are looking for is to produce a reduction in pipe size so that the water velocity increases to pull air from the outside into the pipe.
Normal Pipe size. —> Reduction. —-> Normal size
Procedure to Make a Venturi –
- At the point where the reduction is located, drill a hole into the tube.
- The hole should be large enough so that the tube fits snug into it.
- The tube should be cut at a 60 degree angle at the end
- The tube should be inserted so that the angled side of the tube is facing away from the direction of the water flow.
This creates a further drop in pressure and sucks air into the pipe.
- The water pump should have a high flow rate in order to create a good enough drop in pressure for air to be sucked in.
- The venturi should be kept close to the surface of the water
- The air intake should always be kept out of the water
- Use aquarium grade silicone to fill any gaps where connections are made.
Venturi Aerator made From a PVC Elbow
Another version of the aerator takes the form of a tube sticking into the elbow of a pipe facing downwards into the water.
Here at the outer end of the elbow the water has to travel a longer distance than the inner side of the elbow. This causes a pressure drop at the outer side of the elbow which in turn pulls air in the tube from the outside.
The elbow facing downwards gives the water some extra velocity which helps pull more air into the water stream.
This method works similar to that of an Aero foil.
Ready-made Venturi from Amazon –
Now if DIY is not your style you can always get one that is readily available through Amazon.
I have used the hpbg-garden-water 1/2 Inch Venturi from amazon and it has worked well for a long period of time.
Video showing DIY Venturi for Aquaponics
The Take Away
A venturi is very simple and easy to make. Once you follow the basic principle by creating a reduction in pipe size you can make a Venturi.
Other store-bought options work just as well or even better in some cases.
Alternatively, You can totally DIY this project and add that extra aeration to your aquaponic system with simple everyday materials.
So go ahead and try your hand at it!