The Bell Siphon explained… and why I don’t use them anymore

I don’t think there is any part of an aquaponics system that is more misunderstood than a bell siphon. Don’t get me wrong, they are cool, they work (most of the time) and relatively inexpensive to make. If you understand the physics of the bell siphon, how they work and why they’re needed, then you know there is no need for them at all.

As the water slowly fills the grow bed, the level in the bed reaches a point where water flows up and over the stand pipe inside the bell. Water and gravity begin to create a lower pressure inside the

returning water to the aquaponics fish tank

returning water to the aquaponics fish tank

bell as it drains down the standpipe. When the pressure inside the bell is lowered, more water starts flowing down the standpipe until all the air is sucked out by the vacuum. This causes a rush of water down the pipe until the vacuum is broken by intake of air at the bottom of the bell after the bed is empty. The theory is straight forward and should work without any problems at all right?

Bell Siphon Problems

I can’t tell you how many mornings I would get up to check my aquaponics system just to see that the bells were continually draining because the siphon didn’t break. Granted this problem was resolved but other design flaws can also impact the reliability of the bell siphon.

Another problem is they take up space in your grow bed. This problem alone caused me to search for another solution. Roots can start growing down into your bell siphon screen and cause issues with root clogging, not allowing your grow beds to drain effectively.

The next step: External Bell Siphon

I thought moving to an external bell siphon would have solved all of my problems and I could stop worrying about issues I was having with draining my grow bed. For the most part, the external bell siphon did eliminate just about all the problems I was having with my bell siphon. The bed was draining, I didn’t have to worry about roots growing down into the screen, and everything was working great. I was able to sleep without worrying about my grow beds at all. But I’m kind of an aquaponics geek so the wheels in my head kept turning.

I realized that I had spent nearly quadruple the price for an external bell siphon because I effectively attached one water containment to another. While it worked great, and to be honest, was really cool looking when it drained, I didn’t want this to be the final design for my systems in the future. So again, I wanted to simplify the design.

The Bell Siphon alternative: The U Siphon

After seeing a video of an internal U siphon working, I was amazed how fast they drained a grow bed and the reliability they offered. It didn’t click with me because the U siphon was still inside the grow bed, taking up space where I wanted to grow things.

The evolution was simple. The External U Siphon was what I was looking for. Quick, reliable draining of my grow beds. They took up zero space in my grow beds and they were the cheapest thing to make. They work so well, that there was never another reason for me to use a bell siphon ever again.

The trick to a U Siphon is simple: The bottom of the “U” is the desired water level in your grow bed. You can raise or lower your water level in your grow beds by shorting the inlet pipe. This is important to keep algae from growing on your grow media. The second part of the U siphon is the length of the outlet of the “U”. Make sure the outlet is a good 4 or 5 inches lower than your bulkhead fitting on the bottom of the grow bed. This will allow enough vacuum to be created until it becomes self-sustaining drain and empties your grow bed.

The Bell Siphon VS the U Siphon

Which one is better? Who am I to tell you what you should use. Bell siphons are cool, when they work, they work well. For me the U Siphon is what I’m looking for because it’s so easy and less expensive and I can focus on better designs in other parts of my aqauponics system. My advice, give both a try and see what you like.

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