Bell siphons are a staple of aquaponic gardening for good reason. These clever devices harness physics to automatically drain and refill your grow bed, providing a continuous cycle of fresh air and nutrient-rich water to your plants’ roots.
With a little cleaning and a steady flow of water, a bell siphon can operate indefinitely without needing electricity, a timer, or even your help getting started! Your plants (and wallet) will thank you.
What is a Bell Siphon?
A bell siphon is used to fill and drain your aquaponic grow bed continuously and automatically. It’s a simple and reliable autosiphon that starts and stops on its own depending on the level of water around it.
As the bed fills with water, it automatically starts to siphon the water out and down until it reaches a preset level, where it automatically stops. This allows the grow bed to refill to a certain point when the siphon automatically starts again. As long as water is flowing into the grow bed, the siphon will continue this cycle without the need for a pump.
Why is a Bell Siphon Necessary in Aquaponics?
The continuous rise and fall of the water level is important for the health of your aquaponic garden. It helps to oxygenate plant roots to help them absorb more nutrients and distribute those nutrients throughout the system. This method is known as ebb-and-flow aquaponics, sometimes also called flood-and-drain.
You can use any type of siphon to achieve this, but there are a lot of advantages to choosing a bell siphon in particular. An alternative to the bell siphon is a water pump regulated by an electronic timer.
Benefits of Using a Bell Siphon
Bell siphons are an aquaponic gardening favorite. They are simple, reliable, and offer a host of benefits to both you and your plants.
Increase Root Aeration for Healthier Plants
Bell siphons keep the oxygen and nutrient levels of your plants in balance.
The constant flooding and draining that a bell siphon creates is extremely beneficial for the health of your aquaponic plants. When the siphon drains the grow bed, the entire plant root is exposed to the air, allowing thorough oxygenation. With good oxygen intake, your plants are better able to absorb nutrients when the water returns.
Prevent Water Stagnation to Eliminate Mold and Bacteria
Stagnant water can quickly become home to mold and bacteria or attract pests like mosquitos and rodents. The continuous ebb and flow created by a bell siphon prevents water stagnation, keeping your water clean and healthy.
Automate Your Pump for Maximum Efficiency
Manually draining and refilling your grow bed is time-consuming and laborious. Bell siphons are an efficient way to automate the process without the need for a timer, leaving you with more time to enjoy the garden. Once you have determined the optimal flow rate for your grow bed, your bell siphon will maintain that cycle at a consistent rate without requiring any additional effort.
Keep Maintenance Simple with a Reliable System
Because a bell siphon is a simple device, it’s easy to set up and maintain. Routine cleaning will keep your siphon running indefinitely. The components are also simple to buy or create from items available at any hardware store, so you can make replacements and upgrades at any time on any budget.
Keep Your Garden Independent of Electricity
Bell siphons work on physics alone and don’t require any electricity or manual input to operate. They can save money on your electricity bill, as well as keep your aquaponic garden running in case of a power outage. This makes it an attractive option for those interested in self-sustainable and off-the-grid farming practices.
How a Bell Siphon Works
It may seem complicated, but the bell siphon is actually a simple device that anyone can create with a few pipes and connectors. Let’s take a look inside.
The Science Behind a Bell Siphon
The fundamental idea behind a bell siphon is Bernoulli’s Principle, which is a concept in fluid mechanics. It deals with the relationship between the pressure and the speed of a liquid.
If you’ve ever drained water out of one container and into another one below it is using a single tube, you’ve experienced this effect firsthand. At the highest point of the siphon, you’ve created a vacuum because the pressure there is lower than atmospheric pressure. This allows the atmospheric pressure outside the tube to push water up and over the peak of the siphon. Gravity takes things from there and drains all the water from the higher container into the lower one. We use these kinds of simple siphons for everything from draining a fish tank to borrowing some gasoline from a car.
The obvious downside is that for this simple siphon to work, you need to help it get started by removing all the air from the tube, either by sucking it out or filling the tube with liquid. That’s where a bell siphon comes in: bell siphons are “self-priming” or automatic, meaning they need no help from you to run in a continuous cycle.
Components of a Bell Siphon
A bell siphon is a simple device with three main components:
- Reservoir – the main container for water to drain in and out of. In hydroponics, this might include your grow bed area.
- Bell – a bell-shaped container for the riser that allows low pressure to build underneath it, forcing water through the riser. In some models, the bell will consist of two separate pieces: a bell pipe and a bell cap.
- Riser or Standpipe – a pipe that sits inside the bell. It allows air in and water out at different stages of the cycle.
Bell siphons designed for hydroponics often have some additional parts to help them run more smoothly in your grow bed. These include:
- Reducer – a section of pipe that narrows the flow of water into the riser to help create a smooth transition.
- Media Guard – a container with holes in it to allow smooth water flow whilst keeping grow medium out to prevent clogging.
- Bulkhead – this holds the riser in position in your grow bed.
- Outlet Pipe or Drainpipe – a pipe extending from the bottom of the device and into the fish tank below.
How a Bell Siphon Operates
Here’s how a bell siphon works:
- Water flows in from above to fill the reservoir (grow bed). As the water level rises, the entire surface of the water is exposed to atmospheric pressure: both outside the bell from the open top of the reservoir, and inside the bell via the riser.
- The water rises enough to fill the bell. When it does this, it forms a seal over the top of the riser pipe, cutting off its access to atmospheric pressure.
- This causes the water to fall through the riser.
- The falling water creates a vacuum inside the bell. Like in the simple siphon discussed above, the vacuum draws more water from the reservoir up into the bell. It then flows down and out through the riser.
- When the water level drops below the bell, it allows air to enter the bell and breaks the siphon.
- The remaining water drains out through the riser. This returns the pressure inside the bell to atmospheric pressure.
- The process starts again. This will continue for as long as water is flowing into the reservoir.
Where Bell Siphons Are Used
Bell siphons have a wide range of practical uses. You might encounter them in:
- Septic systems
- Automatically flushing toilets and urinals
- Pythagoras cups
- And, of course, hydroponics and aquaponics
Choosing a Bell Siphon
Selecting or making the right bell siphon for your aquaponic setup doesn’t have to be expensive or complicated.
Sizing Your Bell Siphon
The best size siphon for your grow bed depends on its size. A grow bed with a larger volume will need a larger diameter bell siphon to drain it.
The most optimal ratio of bell size to drain size is 2:1, meaning that the tube used to create the bell should be twice the size of the riser. For example, a 1-inch riser will need a 2-inch bell.
Ready-made bell siphon kits will often specify the ideal depth of your grow bed or grow medium, but you can also use these sizes as a general guide:
- For a 4-cubic-foot (or 30-gallon) grow bed with measurements of 1ft x 4ft x 1ft, a 1-inch diameter bell with a 0.5-inch diameter riser is effective.
- For a 16-cubic-foot (or 120-gallon) grow bed with measurements of 4ft x 4ft x 1ft, you will want a bell with a 2-inch diameter and a riser with a 1-inch diameter.
- For a 24-cubic-foot (or 180-gallon) grow bed with measurements of 4ft x 6ft x 1ft, a 3-inch diameter bell with a 1.5-inch diameter riser is effective.
- For a 32-cubic-foot (or 240-gallon) grow bed with measurements of 4ft x 8ft x 1ft, you will want a bell with a 4-inch diameter and a riser with a 2-inch diameter.
Making Your Own Bell Siphon
Many aquaponic gardeners choose to DIY their bell siphon. There are several benefits to the DIY approach:
- It’s very affordable.
- All the materials should be readily available at your local hardware store.
- You’ll be able to create a siphon that fits your system perfectly.
- It’s a great opportunity to learn hands-on how your aquaponics garden works.
- By making it yourself, you’ll be more confident when it’s time to carry out maintenance and repairs.
Rob Bob’s Aquaponics & Backyard Farm has an excellent tutorial (see below). If you prefer written instructions, you can follow the guide by the University of Hawai’i.
Buying a Bell Siphon Kit
If you don’t feel ready to make your own, you can purchase ready-to-install bell siphon kits from most aquaponic suppliers. Buying a bell siphon kit is a great option if you want to get set up sooner and limit your margin of error.
Here are some readily available options to get you started:
- Aquaponics Auto Bell Siphon Kit 6″ Media or Smaller from Smoky Mountain Aquaponics (via Amazon)
- Aquaponics Fail Safe Auto Bell Siphon Kit For IBC 8″ Media from Smoky Mountain Aquaponics (via Amazon)
- Aquaponics Bell Siphon Kit For IBC Growbed 12″ Media from Smoky Mountain Aquaponics (via Amazon)
Frequently Asked Questions and Troubleshooting
Answers to some of the most common questions and issues when using a bell siphon in your aquaponics garden setup.
Can a Bell Siphon Pump Water Uphill?
No. Because of the physics involved, your bell siphon can only move water from a higher reservoir (such as your grow bed) to a lower reservoir (such as your fish tank). The water must end at a lower point than it started. If you plan to recycle the water through your system again, you will need a pump for that part of the process.
My Bell Siphon Won’t Start, and the Water Level Remains High
Your bell siphon should self-prime, meaning it starts automatically when the water reaches a certain level. If your bell siphon will not start, it is under-siphoning. You can troubleshoot this by:
- Checking the joints and seals, particularly if your bell is made up of a bell pipe and separate cap. These need to be airtight for the siphon to operate.
- Making sure your siphon is anchored to the bottom of your grow bed, and that no grow medium has worked its way into the system.
- Increasing the flow rate of your incoming water. If your setup is new, you can experiment by increasing the flow rate. If you have an existing setup that has recently encountered this problem, you should check to see if anything has altered the flow rate, such as debris blocking your pump.
My Bell Siphon Won’t Let My Tank Refill, and the Water Level Remains Low
Your bell siphon should automatically stop siphoning water when it reaches a particular low level and reactivate only once the water reaches its high point again. If your siphon continues draining without letting the tank refill, it is over-siphoning. In this case, you can try:
- Cleaning your bell siphon. It’s important to check that your bell siphon is clean and free of debris, grow medium, and plant roots.
- Decreasing the flow rate of water into the tank.
- Checking that your drainpipe isn’t submerged in water, particularly if your fish tank is directly below your grow bed. If the drainpipe sits directly in the water below without an air gap, your siphon will not stop.
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