When a fluid passes through a constricted space, it undergoes the Venturi effect. A Venturi water pump utilizes this effect for increased water flow. There are many different engineering applications of this effect, for application in aquaponics we are interested in recirculating and aerating water. Before discussing how to make a Venturi water pump for aquaponics, it is important to discuss the principle behind it.
The Venturi effect is a direct application of Bernoulli’s Principle. Bernoulli’s principle takes into consideration a fluid passing through a constricted space and the conservation of mechanical energy. As a fluid flows through a smaller area, its pressure applied on surfaces decreases and is converted into kinetic energy. This increase in kinetic energy increases the velocity of the fluid through the smaller area.
An interesting fact is that this is the same principle planes use for flight, for a better understanding, here’s how NASA explains this principle.
When Should You Use A Venturi Water Pump and How?
Now that we understand Bernoulli’s principle and what the Venturi effect is, when can this be applied? It is important to note that the Venturi effect works on the assumption that the fluid in the pipe is non-compressible. This means that if the pipe is not full or has air mixed in, there is no Venturi effect.
Creating Turbulence In Your Water Increases Aeration
Creating a venturi effect from your water pipes could aerate the water by the increased velocity from the exit pipe. This increase in velocity creates turbulence that mixes air bubbles with your water, increasing the dissolved oxygen (DO). The increase in velocity also generates a negative pressure differential, sucking more air into your pipe to mix in with the water.
This could be used in both the aquaculture and hydroponic components of your tank; both of which require dissolved oxygen. In an aquaculture tank, it is best to avoid creating too much turbulence as this will stress the fish. While in a hydroponics unit, avoid creating too much water vapors as this will increase root rot.
Learn more about: What Is An Airstone?
How To DIY Venturi Vacuum Pump
First, you need to constrict the water flow in the pipe and there are three ways to do this;
- Place a solid object inside your pipe to constrict the flow of water. The solid object should be fixed in place and withstand the oncoming water pressure. Here is an example of a marble being fixed into position to constrict the flow of water.
- Reduce your pipe to a smaller diameter using a reducer.
- Using a perforated membrane inside your pipe will also reduce the area for water to flow. This constricts flow and generates multiple streams of water.
The next step is to add an air hole with a tube going inwards to suck air into the pipe. Make sure that there is no leak by sealing the hole around the tube. This utilizes the negative pressure differential to add air into the pipe. To make sure you are triggering the Venturi effect, you should feel a slight vacuum from the tube connected to the air hole. Here is a great example of how it would look, credits to Rob Bob’s Aquaponics & Backyard Farm.
In using the Venturi effect for your aquaculture tank or media bed, I would suggest adding it above the water to increase interaction with air.
For using a Venturi pump in your hydroponics unit, mainly if you are using a raft type, I would suggest placing the exit pipe underwater. This increases circulation in the water, evening out the distribution of nutrients in your hydroponics component. This may be more difficult in a media bed due to the solid media blocking the circulation.
How To Make A Venturi Pump In An Air Lift System
It is important to note that using the Venturi effect creates an extra load on your pump. The difference in pressure backwashes to the pump and could wear it down faster. I do not suggest using the Venturi effect for aquarium pumps as the backwash pressure may damage your pump.
If you are using an airlift system to circulate water vertically, the Venturi effect could be useful to generate more lift and aeration. Air lift systems utilize air pressure to push water up a pipe, this coupled with the Venturi effect maximizes your water’s exit velocity and increases aeration. Here is an explanation of what an airlift system is by Glenn Martinez of Olomana Gardens. There are multiple designs to an airlift system and we will be discussing them in detail in a later article.
There are two ways to use the Venturi effect in an airlift system;
1. By reducing the area where water flows in your airlift system, the consistent air pressure that pushes the water through will be constricted and generate velocity and turbulence. I have observed that in my airlift system, the smaller space is between the external pipe and internal pipe, the more lift and turbulence I generated. Though water travels higher, the amount of water is less. This is due to the amount of backwash because there is less pressure that’s able to push a large volume of water vertically.
2. Using a perforated pipe increases turbulence and creates microbubbles that help aerate the water. This can be done by simply drilling multiple holes in your inner pipe
Remember that the Venturi effect is only applicable to non-compressible fluids, meaning this has to be applied in a pipe that is either full of water or fully pressurized with air.
Remember that the Venturi water pump is only a concept. Thus the application of the Venturi effect is versatile and could benefit your system in different ways. Though aeration is the common application of the Venturi pump, it could also help in circulation and generating vertical lift. There are different ways to create your own Venturi pump, it is up to the grower to decide based on the available materials and creativity.