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.

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

Parts:

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" 90^o elbow

Tools:

• Drill or Dremel

• Drill bit (1/8")

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.

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.

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.