How to Build a Siphon Part 1


Hey there Trifecta fans.

In today’s blog post we are going to teach you how to build your own bell siphon. But first let’s talk about what a bell siphon is and explain the benefits it will bring to your media beds and overall aquaponic system health.

So let’s start with the basics. First what is a siphon? A siphon at it’s simplest is a device that uses water’s inclination to move towards level and moves water from a high point to a low point through tubing. The force of gravity is integral to siphoning and especially integral in creating a bell siphon.

Before we get to the specifics of how to build a bell siphon lets discuss why we need siphons in media beds in the first place. At is essence it is because in aquaponics we desire aerobic bacteria to be present in our system and want to discourage the growth of anaerobic bacteria. Aerobic bacteria need oxygen in order to survive. In a media bed this can be difficult to achieve without outside manipulation by us. In a raft bed/deep water culture system and within our fish tanks we achieve this through the use of airstones. There is no need for outside manipulation other than the installation of airstones.

In a media bed however, the water fills the bed up but die to the media air stones are pretty impractical to introduce oxygen. There are two common methods to deal with this in aquaponics. The first is flood and train. In media bed systems water flows into the media bed via a pump. In flood and drain systems you insert two standpipes into the media at two different heights. A short standpipe acts as the minimum water level and a tall standpipe acts as the maximum water level for the beds.

As water flows into the bed it fills up to the first  shorter standpipe and begins overflowing, in these systems you need to make sure that our pump can outperform the draining of the first siphon. This will allow the water to continue to rise to the height of the second standpipe and it overflows through that pipe as well preventing the water from rising higher or overflowing your media bed. The pump in this scenario also must be put on a timer. For example you may put your pump on a timer so it turns on for fifteen minutes every hour.

This method, known as flood and drain, comes with a few complications. First, the need for two standpipes with media guards takes away precious real estate for plants in your beds. Second, the need you need to calculate flow rates of your pump and stand pipes in order to ensure that your pump will out perform the draining in the first standpipe but not outperform the draining of the short and tall standpipes as that would result in overflowing your media bed.

Finally, due to the fact that the pump needs to put on a timer and is shut on and off once an hour this stresses the pump and can shorten its lifespan significantly. For these reasons we are not a fan of this style of flood and drain.

So let’s look at how the bell siphon works. The bell siphon is just four main components. These are a standpipe, overflow reducer, the bell (pipe with a cap placed over and around the standpipe) and a media guard sheltering the internal unit and preventing media from draining out of the bed through the siphon.

When put together, the standpipe is on the inside of the unit. It is covered by the bell piece which is surrounded by the media guard. The bell siphon operates similarly to a standpipe in the flood and drain scenario. As water pumps into the bed it rises to the top of the standpipe with the overflow reducer on top. As water begins to overflow it exits through the standpipe and out the bed into a sump or fish tank.

Because we have a reducer on top of our stand it slows the flow of water down slightly at first. This results in the creation of a small pressure build up. This is where the bell piece comes in. Water builds up in the bell piece and eventually overcomes the restriction of flow caused by our reducer. This creates a strong flow of water out of the standpipe known as the “flush”. The “flush” also starts the siphoning. Because the bell piece has a cap and due to the physics behind the design the water continues “flushing”.

The force of gravity that is pulling the water down the standpipe and continuously pulls water up the bell chamber and over the standpipe until there is no more water in the bed. It automatically drains the entire bed. All without altering the pump configuration, without electricity and without any moving parts. So long as your pump maintains the proper pressure and you install the siphon correctly it will never break. In addition the strength with which the bed drains pulls additional oxygen down into the media bed.

As we recall, that is the goal of this exercise is to provide oxygen to our media beds. This is to ensure that the aerobic bacteria get the oxygen they need to survive.

The bell siphon offers a couple of benefits besides increased oxygen to the media and the plants. The bell siphon removes the need for a timer. It regulates the bed automatically. This extends the life of the pump and removes the need for extra equipment for you to purchase. Depending on the size of your system and how you have it set up, if you have your system set up so that it drains into your fish tank it also removes the need for air stones in your fish tank.

The force created by the siphoning provides adequate viscosity and therefor oxygen for your fish. In the upcoming parts in this series we have a video of this set-up in action. Due to it’s versatility and ability to save you money on additional equipment, coupled with increased efficiency for your system we like the bell siphon over timed flood and drain for regulating your media beds.

In part two of this series we will go through step by step how you can build your own siphon. We’ll demonstrate on a mini media bed system directly over a fish tank. It almost doubles as a how to convert a small fish tank to an aquaponics system! In part three of this series we will offer variations we have been experimenting with that we like and how to build or incorporate them.

Finally, part three will include links to parts on the parts list. That way you can build in confidence knowing you are using the same parts as us. This removes the uncertainty we’ve all felt heading down the aisle of Home Depot or pouring through the Grainger catalog unsure if we were supposed to get coupling or bushing, males or females etc. The only hard part in building a siphon is sourcing the right parts.

We’ll take care of that for you so if you’re interested stay tuned for Part Two and Part Three in our How to Build a Siphon Series.

The Trifecta Team


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