Make a Bell Siphon

Introduction: Make a Bell Siphon

A bell siphon is used in ebb and flow aquaponics and hydroponics systems in order to regulate the flow of water.  In an ebb and flow (also known as flood and drain) system water is pumped into the grow bed.  At a specific point (usually 2 inches below the surface) the water drains via the bell siphon.  When the water reaches the bottom you will hear the classic gurgle indicating the end of the drain phase.  The process will then repeat itself over and over again.  The bell siphon is a such an important part of any ebb and flow system that getting it right is crucial.  In this instructable I'll show you how to make your own, and tweak it to your needs.

Step 1: Parts and Tools

Here's what you will need to make your own bell siphon:


Gravel Guard

  • 1 - 3" PVC pipe (approximately 12" long)

Bell Dome

  • 1 - 2" PVC pipe (approximately 10" long)
  • 1 - 2" PVC cap

Bell Siphon

  • 1 - 3/4" PVC pipe (approximately 6" long)
  • 1 - 3/4" to 1 1/2" bell adapter

Grow Bed Connections

  • 1 - 3/4" Male adapter (thread to slip)
  • 1 - 3/4" Female adapter (thread to slip)
  • 2 - #18 o-rings

Drain Pipe

  • 2 - 3/4" PVC pipe 4" long
  • 2 - 3/4" 90o elbow


Step 2: Preparing the Dome and Guard

I created a guide that you can use to make clean and equally spaced holes around the bottom of your gravel guard and bell dome.  First download the Bell Holes Guide Document and print it.  You will likely get an error message saying, "The margins of section 1 are outside the printable area of the page.  Do you want to continue?"  Click Yes.  Cut out the two guides, wrap each guide around the bottom of your PVC pipes (the 3" gravel guard, and the 2" Bell dome), and tape them in place.  Use the guide to drill holes around the bottom of each pipe.  Remove the guides and clean up any left over PVC dust or tags.

Step 3: Building the Siphon

Follow the Bell Siphon Diagram to put the siphon together.  Start with the male and female adapters.  Take the male adapter and slip a #18 o-ring over the threads.  Insert the adapter through the access hole in the grow bed.  Slip another #18 o-ring over the top of the male threads.  Screw the female adapter to the male adapter (no jokes here folks) making sure you have a tight connection.  Its not necessary to get the tools to tighten it, hand tight or even slightly less than is fine (you'll be checking for leaks later anyways so it's not necessary to overdue it).  Slip a 6" piece of 3/4" PVC pipe into the female adapter (The diagram says this is 4", start with 6" and check the water line when you're done.  If the water line is too high, make a note and adjust this pipe as needed).  Slip the 3/4" to 1 1/2" bell adapter on top of the 3/4" PVC pipe .  To create an effective drain flow it is important that the opening of the Bell is double the size of the pipe (3/4" * 2 = 1 1/2").  Slide the PVC Bell Dome (Again, start with 10" and adjust if the water line is too high) over the drain pipe, and the PVC stone guard over this.  For the underside of the grow bed slide a piece of 3/4" pipe into the bottom of the male adapter.  Slide a 3/4" PVC 90 into the bottom of this pipe, and from there another 3/4" PVC pipe and another 90.  Depending on the location of the fish tank you will need to size these last two pipes appropriately.  If the horizontal pipe is long I suggest using a T-fitting at the end instead of a 90.  This will help the flow of the draining action.

Step 4: Test the Bell Siphon

After you have your bell siphon put together feel free to test it by filling the tank.  Take note of the water level where the siphon starts, and especially the max height of the water.  The max height of the water should be 2" below the grow media surface.  If you need to adjust any pipes now is the time to do it.  If your water line is an inch above the mark, take an inch off the top of the siphon pipe, and an inch off the top of the bell dome.

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    16 Discussions

    Any suggestions...Followed directions. Very excited to build but my bell siphon empties the grow bed faster than my 750 gph pump can pump. I am feeding the grow bed with a half inch hose, should I go up to a 3/4 inch hose?

    great help. my inner tube was to high so the "bell" couldnt catch enough water for suction to set in properly. it just drained slowly.
    your advice on a proper bell-size fixed that issue.

    as you can see i have a little different approach, the $1 version with:
    - piece of 1.5" pipe, lenght 6"
    - cut off 33 cl plastic bottle (for the bell), 3" diameter, length 8.5"
    - cut off 1.5l plastic bottle for the stone guard.

    3 replies

    oh sheesh the 2inch cap goes on the 2inch bell dome the three quarter to 1 and1half adapter does on top of the three quarter pipe

    Nice approach to the bell siphon with plastic bottles, I like it!

    Love it. Great way of making one. Does it work now?

    Excellent works, thank you.

    Hello, I am still trying to assemble the syphon. I've purchased two different 3/4-1 1/2" adapter. Neither fit in the 2" bell dome. Any suggestions?

    What is the purpose of the bell reducer coupling?

    .doc links are not working :( error 403, that is to say that we don't have permission to download it...

    1 reply

    I'm not sure why the file isn't working; however it was very easy to make. I made a simple pattern in Excel marking each hole. I printed the document and wrapped it around the pipe to use for the template.

    Sorry but your page and links are just not working. It is a bit frustrating.

    can you email me the drill template plz it says it forbiden my email is thank u

    I was hoping for step by step pictures. This info is available on most other aquaponics and barrelponics instructables.

    Thank you for sharing this. Unfortunately I'm not able to download the Bell_Hole_Guides.doc, its says "Request forbidden by administrative rules."

    Could you please email it to me,

    Thanks a lot :)

    1 reply