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Ultimate Guide On How To Build A DIY Bell Siphon

A bell siphon is one of the most important components in any media based aquaponics system. It is responsible for regulating the water levels in the grow bed via a flood and drain cycle that constantly provides fresh water at regular intervals. Bell Siphons are utilized in the Ebb and Flow hydroponics technique. Media based aquaponics systems are built upon the exact same Ebb and Flow concept, with the inclusion of an additional aquaculture stage, therefore bell siphons also see used in these setups.

How to DIY Bell Siphon
Image Credit: Bob's Aquaponics & Backyard Farm.

Components of a Bell Siphon

Consisting of just handful of parts, bell siphons are simple to construct, reliable and durable; if properly constructed and installed will last for several grows with minimal maintenance. The few parts that make up this device include:

  • Media Guard/Shroud
  • Bell Cap
  • Siphon Pipe
  • Standpipe
  • Reducer
  • Bulk Head
  • Drain Outlet
  • Elbow connector

How a Bell Siphon Works

The Main Components at Work

A bell siphon works by leveraging the properties of water, pressure and gravity. It does so in a wonderfully simple way that is based upon Bernoulli’s law, which states: once enough fluid is drawn out of the top bottle, pressure of the gas trapped inside it will lessen until at some point the siphon stops operating. The three main components that make a bell siphon work are:

  1. The Media Guard, or Shroud, features slits/holes that allow water to flow into the bell whilst preventing unwanted material entering.
  2. The Bell, has holes cut into the bottom, which allows water to flow to the standpipe to help initiate the siphon
  3. The standpipe, or the drainage outlet, sets the max height of the water level, lets water escape into the reservoir/sump tank

Why Diameter and Placement Are Important

The diameter of these parts is extremely important in making the siphon fire and break smoothly. The placement of bell siphon is also crucial to ensure efficient drainage. It is generally advised to install the device in the middle of the grow bed to maximize the drainage capabilities. The bell siphon sits within the grow bed, surrounded by grow media.

Media Guard/Shroud: The bell cap atop the media guard should stand a few cms, or roughly an inch, above the grow media. Ensure that sure nothing obscures the slits/holes in bell siphon as any disruption to the water’s flow can cause the siphon to cease working.

Bell/Siphon Pipe: Inside the shroud the bell stands roughly level with the grow media. It features holes in the bottom that allow water to flow in and up around the standpipe. The diameter of the bell pipe should be smaller than the shroud by a ratio of 2:1; a ratio mirrored throughout the design.

Standpipe: Inside the bell the standpipe sets the height of the water level, which should sit a few cms, or just shy of an inch, below the surface of the grow media. This keeps the grow media clean and prevents algae from growing on the surface.

Note: The standpipe should be connected to a reducer to assist the initiation of the siphon. The diameter of the reducer should decrease the size at the same ratio of 2:1. Therefore and overview of each diameter would look like the following:

  • Media Guard =4” > Bell/Siphon Pipe =2” > Reducer =2-1” > Standpipe =1”

The Flood and Drain Cycle

  • Water is pumped into the grow bed where it then enters the bell siphon through the slits/holes in the media guard.
  • Water then passes through the slits/holes in the bottom of the siphon pipe to fill the bell chamber.
  • As water fills the grow bed and the bell, air pressure remains equal as the water is exposed to the atmosphere in the grow bed, and through the standpipe within the bell.
  • Once the water rises above the entrance to the standpipe it creates a seal, which blocks off the inner bell from the atmosphere, which in turn creates a vacuum.
  • Then as the water falls, the vacuum continues to draw it into the bell and out through the standpipe, until air is allowed to enter the bell from same slits the water originally did, in the bottom of the siphon pipe.
  • This rush of air breaks the siphon, allowing the cycle to start over again.

Advantages of DIY Bell Siphon

When it comes to installing a bell siphon many growers opt for the DIY method as it provides a number of benefits over pre-built, store bought options. These off-the-shelf designs are few and far between, and with much fewer options you’re often forced to make unfavorable compromises. Going the DIY route allows you to create a bell siphon to meet any size specification you require (within certain guidelines that states the standpipe, reducer, and siphon pipe must each increase in size by a ratio of 2:1, respectively).

Materials, parts, connectors and accessories available for plumbing and drainage make the build straightforward and accessible to almost anyone. The parts are durable, easy to work with and provide an aesthetic that looks purpose built and professionally made. Benefits of building your own DIY bell siphon include:

  • Affordable
  • Off the shelf parts
  • Variety of dimensions from off-the-shelf-parts
  • Easy to build
  • Easy to maintain
  • Easy to fix/replace
DIY Bell Siphon Install
Image Credit: Bob's Aquaponics & Backyard Farm.

How to Build a DIY Bell Siphon

If you’re new to bell siphons and the underlying concept that makes them work, check out our in-depth introduction to bell siphons, ‘Ultimate Guide To How Bell Siphons Work.’ This article takes a deep dive into bell siphons; it covers all aspects of the device, as well as the theory behind its function, from a perspective that beginners can understand.

Having a better understanding of how bell siphons work can be extremely helpful when building your own DIY version. Armed with a solid knowledge base you’ll be less likely to make mistakes, you’ll be able to spot mistakes easier, in some cases before they’ve even occurred, you’ll problem solve better, and the whole build will just be that little bit less complicated.

Step-by-Step DIY Bell Siphone Build Process

Sizing Parts

Ensuring the diameter of these parts increases by a ratio of 2:1 is the first step in dialing in the bell siphon so it works consistently. As a general rule of thumb, a good starting point for the diameter of each part would be as follows.

  • 16-cubic-ft/120-gallon grow bed should have a 2” bell > 1” reducer > 0.5” stand pipe
  • 24-cubic-ft/180-gallon grow bed should have a 3” bell > 1.5” reducer > 0.75 stand pipe
  • 32-cubic-ft/240-gallon grow bed should have a 4” bell > 2” reducer > 1” stand pipe

The height of these parts, and thus the resulting volume, is equally as important to ensure the siphon runs smoothly. These dimensions will largely be determined by the depth of the grow bed, so you can simply start by measuring and cutting lengths oversized/taller to accommodate any adjustments in the build process.

Media Guard/Shroud

  • Next comes the Media Guard/Shroud. Choose the appropriate size and cutting the pipe to the correct length.
  • Cut out holes or slits in the pipe, do this around the bottom half only as it helps force the flow of water.
  • Next cut and place a shroud cap on top of the guard, you can use plumbers tape, or even just hot glue to seal the cap airtight.
  • Finally install the end cap, which will allow the device to be attached to the bottom of the grow bed via the bulkhead. You’ll also want to drill holes in the end cap to further aid the flow of water.
DIY Bell Siphon Media Guard
Image Credit: Bob's Aquaponics & Backyard Farm.

Bell/Siphon Pipe

  • Next comes the Bell/Siphon Pipe, this sits over the standpipe and features an airtight bell cap, as well as slits/holes in the bottom to allow water to flow in. Cut the bell to length, the cap should stand a few cms/an inches or so above the standpipe.
  • You can use glue or a silicone adhesive to seal the bell cap if you’re still having issues with leaks.
DIY Bell Siphon Bell and Standpipe
Image Credit: Bob's Aquaponics & Backyard Farm.
DIY Bell Siphon Bell Cap
Image Credit: Bob's Aquaponics & Backyard Farm.


  • Next comes the standpipe. Note: the dimensions are sure to change based on the size of your setup, however the basic construction method remains the same.
  • As mentioned, the standpipe sets the height of the water in the grow bed. This should be slightly below the surface of the grow media; this helps keep the media clean and free from algae.
DIY Bell Siphon Standpipe
Image Credit: Bob's Aquaponics & Backyard Farm.


  • A top the standpipe you can attach a reducer. This should have an opening twice the size of the diameter of the standpipe, a 2:1 ratio, and should be roughly half the length of the standpipe. Note: there should be enough clearance for water to flow between the top of the reducer and ceiling of the bell cap.
  • Note: Remember to account for the length of these parts when calculating the total length/height of the standpipe.


  • At the bottom of the standpipe sits a valve sock and bulkhead fitting. Note that you may need an adaptor bush to connect the valve socket.
  • It’s also possible to do away with the vale socket and bulk head fitting. This can be replaced with a threaded foster adaptor, as well as an O-ring, and/or washer. Plumber’s tape can help things airtight here if you’re having problems with leaks.
  • An even simpler solution would be to use a Uniseal. This simply requires the correct size hole to be drilled, through which the pipe and rubber seal is pushed to form an airtight friction fit seal.
DIY Bell Siphon Bulk Head
Image Credit: Bob's Aquaponics & Backyard Farm
DIY Bell Siphon UniSeal
Image Credit: Bob's Aquaponics & Backyard Farm
DIY Bell Siphon Outlet Elbow
Image Credit: Bob's Aquaponics & Backyard Farm

Drain Outlet

  • At the bottom of the standpipe and bulkhead, you’ll want to extend the outlet pipe and install an elbow connector to place a 90-degree (more if possible) bend the direction of flow. This helps prevent air travelling back up the pipe, which can cause the siphon to break prematurely and stop working.
DIY Bell Siphon Drain Outlet
Image Credit: Bob's Aquaponics & Backyard Farm.

In Conclusion

Building your own DIY bell siphon isn’t just a useful project; it’s also an extremely satisfying one. In addition to saving you some money, building your own gives you first hand insight into how the device works, and by understanding exactly what makes the automatic siphon action, you’ll be able to spot any problems easier then fix them without waiting for additional assistance; a move that could be fatal to the system.

Trouble Shooting
If you’re having issues with your bell siphon operating properly, there are several common problems, and corresponding fixes, that’ll have your system running smoothly in no time. For common troubleshooting tips check out our in depth introduction to bell siphons, and if you can’t find what you’re looking for there, feel free to drop us a msg and we’ll not only respond with the correct information, we’ll also add the advice to the appropriate article/post/page.

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