How Does A Bell Siphon Work?

Last Updated on January 23, 2022 by Fabiola L.

Bell siphons drain water when it reaches a certain height in a grow bed, but you may ask yourself how does a bell siphon work? Commonly used in ebb and flow systems, bell siphons allow you to control the water level in your grow bed. Draining the water in the grow bed allows for the plant roots to go to a dry cycle to avoid overwatering or waterlogging. Bell siphons can be made for aquaponic grow beds to control the water levels of the ebb and flow system.  In this article, we will be discussing how a bell siphon works and how to build and use your own bell siphon.

How Does A Bell Siphon Work?

The mechanism behind bell siphons lies in creating a vacuum that pulls water as it starts to fall down a standing pipe. A bigger pipe with a cap covers the standing pipe while still allowing water to pass through the bottom through teeth. As water rises in your grow bed, it rises up inside the bigger pipe. As water rises higher than the teeth, the air inside the big pipe has nowhere to go but down the standing pipe. This creates a vacuum inside the bigger pipe.

As water reaches the height of your standing pipe, water will begin to fall down. With the vacuum, the bigger pipe will act as a straw, sucking the water down up to the height of the teeth. As the water level reaches the teeth, air will start to rush back in the bell siphon and stop the suction. As the suction stops, water will start to fill the grow bed again.

How To Make and Use A Bell Siphon?

To make a bell siphon for your aquaponics grow bed or components, follow these simple steps

  1. Measure intended maximum water height inside your grow bed or component.
  2. Drill a hole where the water and pipe should exit. The pipe should be standing vertically so it is best to set it perpendicular to the bottom of your grow bed.
  3. Use a male and female PVC adaptor for the drilled hole. It is possible to use any size of pipe, so long as your larger pipe is ½ – 1 inch larger than your standing pipe
  4. Connect a standing pipe to the male and female PVC adaptor facing upwards
  5. Cut the standing pipe to the intended height of your maximum water level
  6. Prepare a larger pipe, ½ – 1 inch larger in diameter
  7. Cover the top part of the bigger pipe, make sure it is airtight
  8. Make sure the bigger pipe touches the bottom of the grow bed.
  9. Determine the minimum water height you want for your grow bed.
  10. Cut out a small piece of the pvc up to the height of your minimum water height to create teeth
  11. Place the bigger pipe on the standing pipe and make sure that the teeth reach the bottom of the grow bed.
  12. Test your bell siphon by filling the grow bed to the height of the standing pipe. Your bell siphon should trigger and flush out the water up to the height of the teeth. Repeat three times to make sure the siphon triggers properly.

 how to make a bell siphon

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When To Use Bell Siphon In Aquaponics

Ebb and flow systems mainly use bell siphons as an automatic siphon to drain the grow bed. Media beds benefit the most from ebb and flow systems because of the drainage. The draining of water allows the plants to have a dry cycle and be exposed to air. Bell siphons allows you to also control the level of water, so in the case of reducing your water level in the grow bed, it is a matter of adjusting the standing pipe’s height. Bell siphons are simple and do not require manual triggers or moving parts. This allows the bell siphon to be a reliable drainage system for your ebb and flow system.

Draining The Water wWll Benefit Your System, Increasing Root Aeration and Avoiding Waterlogging

As the bell siphon drains the water, this exposes the plant roots to air, increasing aeration for your root system. Draining the water in your media bed will also prevent waterlogging for your plants. Waterlogging happens when there is too much water and the roots drown. Plants like chilis are susceptible to overwatering. Plants with low water requirements benefit from the increased aeration and regular draining of water in the grow bed.

How Long To Cycle Between Ebb and Flow

The larger your media bed and slower your flow rate, the longer it will take to fill up and trigger the bell siphon. Personally, I prefer longer cycles between ebb and flow since the longer your water stays in the media bed, the more nutrients are taken up. This will also allow for more nitrogen-fixing bacterial activity to occur. According to a research by Knaus et al., basil grown in a gravel bed with an ebb-and-flow setup produced taller basil plants. Their setup had a faster cycle between ebb and flow, having 6 cycles per half hour. Taller basil plants do not translate to higher yields, although shows the capacity of media beds to support root systems and taller plants. There is no set practice or standard on intervals between ebb and flood and relies on the practitioner on what works best.

How does a bell siphon work relies on the vacuum created between your standing pipe and shroud which creates a suction when it hits a certain height. The advantage of using a bell siphon lies in the flexibility of adjusting the height of your maximum and minimum water levels. In using a bell siphon, be careful of your siphon not triggering. It is best to test your bell siphon before filling your grow bed with media. Bell siphons are simple to build and provide benefits for your plants. Some of the benefits include aeration for plant root systems and preventing waterlogging. Although up to date, there are no standard practices on using ebb-and-flow systems and the optimal interval between ebb and flood.

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