Affnan's Valve - A Detailed Explanations of A Simple Item


First of all I would like to point out that, siphon had been around for a long time dated few hundred years ago. Siphon usage ranging from transferring fluid from one container to another right to flushing the toilet.

Most usage of siphon involved a fixed amount of fluid to be transfer to another container, such usage of siphon don't require it to be operating continuously without human intervention. Toilet flush for example require human input to create the flushing effect from a siphon mechanism, and the flushing stop when cistern is depleted of water. Continuous operation of these siphon are not needed.

In Aquaponics due to the nature of system arrangement, continuous operation of siphon is necessary with constant water flowing into the container. Siphon drawing water out creates "Flood and Drain" cycles that promote Aquaponics balance.

No one living today could claim have invented the siphon, nor claiming pattern for such. However improvement to siphon design to make it reliable or use able to an application can be considered as an Innovation. An Innovation deserve to be recognized if its significantly change the way things being done.

I like to compare, a redesign Siphon to that of a shoe. Shoes has been invented long time ago, however shoes the late Micheal Jackson use for his moon walk was design by him and accepted as a pattern. He may not invent the shoes but he make it better to suit his purpose.

Here it come !!
Explanations that follow below are the results of two years of experimenting and studying the siphon... eight months of experimenting with endless siphon design, most siphon have been tried until this current design is met, and the remaining months to refine the design and understand it principle to tweak and tune it for better function.

What you will find below are the way to make this valve, how to adapt it to your setup and some simple task to do in the event it fail after deployment. A lot of effort was put into this and it would give me great satisfaction if you succeed in using it for your system.

This is the schematic of my bell valve.

I will slowly add here the write up, on how the Siphon function and the various adjustment done to make a siphon function as it did.

Before I proceed in explaining how mine work, let us have a look at the basic stand pipe siphon below and the various method used in an attempt to make it use able in Aquaponics. This is the baseline design for a siphon, what needed to be done is to make changes to this basic design to make it better.

In order to make improvement we must know what are the variables involved in a siphon and how can these variable be change to cause a change in the siphon behavior.

In this basic siphon to get the siphon action started is just a matter of getting water flow into the growbed or container large enough to cause the siphon action. Water flow in rate requires to start this siphoning is directly proportional to the size of the stand tube. Therefore starting a siphon is easy, what difficult is to cut-off that siphon action once water is drained out.

It may appear easy, people that has never make a siphon may think once water is drained out and the siphon will draw air and cause the siphon to stop. However that is not the case with an Aquaponics setup, which has continuous water supply coming into the grow bed.

This water flowing into the bed earlier which much needed to cause the siphon is now the problem in causing this siphon to cut-off. This continuous water in which cause the siphon to refuse to stop and continue to draw water out is call the "Equilibrium Flow".

This is the killer of siphon.

Why do equilibrium flow happen ?
It happens because the water needed to start the siphon is the same or more then that require to sustain a continuous flow.

How do we stop equilibrium flow ?
To stop this equilibrium flow few things needed to be done:

  • Ensuring the difference between water flowing in to make a siphon and water needed to sustain a continuous flow large.
  • Ensuring water flowing out of the siphon at the end of cycle (residual flow) will still be strong enough to pull in air causing the break.
How do we achieve this ?

  • We have to make a siphon to start with less amount of water flow in, to that of the same size basic siphon.
  • Make a siphon with strong residual flow.
Which would make the difference above large enough to ensure no continuous flow is maintain.

But its not a car !
Tuning a siphon is very much like tuning a car for better mileage. To get better gas mileage its a combination of items need to be check or adjusted, fuel air mix adjusted, spark efficiency, timing accuracy and to the extend that tire pressure need to be check. This cumulatively make a car more efficient thus improving mileage.

In a siphon, multiple factor are involved to make it efficient and thus reliable. Some if not all these factor need to be improved to ensure trouble free operation.

Below are various methods use to help this happen and to certain extend helps in achieving this objective.
How do bell siphon achieve this ?
This is a long explaination and thank you for reading it.
Below are variations of my valve. Valve A utilize the elbow, Valve B slight restrictor and Valve C with a longer down tube. All these difference variations do one function, aid in producing siphon action with lesser amount of water flowing in. These various modification to the outlet are part of the tuning for a reliable siphon.

More alteration needed to be done to ensure the margin of flush and equilibrium flow is widen.

Bernoulli's Theorem, Theory of Flight and the lowly siphon
I work in the aerospace industry for almost 30 years, from day one we were taught about the Bernoulli's Principle and on how lift achieve with this principle. I apply this to the valve design to do what it need to do, to create an earlier flushing Siphon.

Extract from :

Bernoulli's Principle is a physical phenomenon that was named after the Swiss scientist Daniel Bernoulli who lived during the eighteenth century. Bernoulli studied the relationship of the speed of a fluid and pressure.

The principle states that "the pressure of a fluid [liquid or gas] decreases as the speed of the fluid increases." Within the same fluid (air in the example of aircraft moving through air), high-speed flow is associated with low pressure, and low-speed flow is associated with high pressure.

This phenomenon applies to the lift produced by the wing of an airplane, i.e., an airfoil. The airfoil is designed so that the air moves more rapidly over its upper surface than its lower surface, thereby decreasing pressure above the airfoil. At the same time, the impact of the air on the lower surface of the airfoil increases the pressure below the airfoil.

This difference between the decreased pressure above and the increased pressure below produces lift. Thus, a wing with more curvature on the top surface (greater camber) has greater lift than a wing with flat surfaces.

Apply the Bernoulli's Theorem to the siphon, this is what you get. There is more to it than just this.
Bernoulli's effect will cause siphon to occur with less water flowing (strong initial flow) and strong residual flow couple with offset stand tube contour to produce unbalance water column and finally the outlet restriction or interference causing even lesser water flowing needed hence assisting siphon lower flow starting and equilibrium flow termination.

Above statement takes into account about 4 or 5 different variables to ensure reliable siphon.

Lower flow siphon starting are due to :
  • Strong initial flow in siphon - Bernoulli's Effect
  • Outlet restriction or interference
  • Longer Exit down tube length - if installation permit
    Equilibrium Flow termination assisted by :
    • Strong residual flow - Bernoulli's Effect
    • Unbalance stand pipe exterior water column due to its funnel shape
    • Longer Exit down tube length - if installation permit
    • Volume Ratio between Stand Pipe exterior water column within the bell to that inside the standpipe and outflow, more in the stand pipe the easier to cut off.
      Making the funnel wider on the top should make it better and making the stand pipe length tall also have same effect on valve to make water cut off easier. Then there will be a limit to the height of the grow bed that prevent this arrangement, but wider funnel is do able.

      To improve further this design, what needed is to make a smooth funnel for the Bernoulli's effect to be maximized.
      This is to the extend that I will explain it, going deeper would require mathematical calculation and formula which I feel not necessary at this point.

      My intention is to have this valve easily made by anyone to such an extend that no one could capitalize on it since its so easily made.

      What else to be tested ?

      I would like to try out the valve below;
      • Valve A is base on the outer stand tube column offset only to cause water unbalance.
      • Valve B was mentioned by that having a pin hole to have air leaked in the bell may assist in water cut off.
      These on their own, may or may not be sufficient to cause the much needed equilibrium cut-off.

      Check here on how to make the : Mini Version

      Check here to see the revised siphon : Part 1 , Part 2 , Part 3 , Part 4 - Final

      Updates : 6th September 2010

      This siphon outlet attachment is made for high water situation on my set. This siphon outlet will provide aeration with high water level and silencing of siphon outlet at lower water level and it can be view here for the completed work. 

      Simplified diagram as below.

      Updates : 18th March 2013

      In this installation Here I remove the bell and use the outer strainer as the bell itself.


      1. Like your site. Keep us updated. Alan

      2. Thanks Alan, I am experimenting with various editing features. Hopefully nothing get missing.

        I've visited your blogsite, you are located in Thailand ?


      3. Thank You Affnan! I have enjoyed reading your Blog. I live in East Texas(USA)and have recently started building an indoor aquaponics system. Your "Bell Siphon" is very simular to the siphons used in septic systems around where I live(but on a smaller scale!),I will try to construct the same siphon using US Standard size PVC(in inches)instead of meteric sizes! Wish me luck!-DAWIII

      4. Thank Dan, good luck on your setup. East Texas, must be a beautiful place. I've been to San Antonio years ago.

      5. I like your invention/improvment to your Bell Siphoning System I am trying to start a Ponic system myself Aero/Hydro/Aqua but living in Brooklyn New York and my place is small but I am going to still try, Thank you for your info on your Bell siphon system (Affnan's Bell Siphon System) best wishes in all your indivers.

      6. @Yahya, thanks for comment, space is not a big problem in Aquaponics. My setup is for small area.. and the growbed over the tank method do not take a lot of space.

      7. Affnan, I'm adding a link to this page onto my blog site. Should help many people who want more explanation and details for building siphons than I can give quickly.

      8. @TC, no problem.. its a pleasure to have you drop in.. :)

      9. Affnan, can you please explain the purpose and function of the '4mm leak hole'?


      10. @Averan

        Primary purpose is to draining the gb if you decide to periodically switches off the pump. It also serve as an indicator to show pumps all is well. If you do not see the drip flow.. it could be pump fail or siphon is dirty and need to be check.

        However, the siphon will work fine even without the hole. Its a recommended option to prevent water remaining in the gb during my switching off period. Basically its take care if you decide to use timer on gb.

        After using this siphon for a long time I would recommend the hole is about 5 mm, to prevent clogging. However even if the hole is clogged the siphon will remain functioning without any problem, its not mandatory to have it.

      11. Additional note : Its best to drill the hole angled downward or slopping down to reduce chances of clogging.

      12. Hello. I wonder if you could help me with a little problem. I want to construct a mega-siphon linking 6 IBC grow beds. Given the information below what diameter stand-pipe and sump drain line should be used to drain the system?

        1. 6 IBC growbeds (350mm) --> will hold ~1200L of water assuming 40% void ratio of gravel.
        2. water inflow will be approximately 3600 Lph to acheive ~3 flood-drain cycles per hour.
        3. using 1-inch line to connect each IBC media grow bed to Mega Siphon.

        Thank you so much.

      13. @scottefontay, you only need to take into account the 3600lt/hr rate to design a siphon. Because this is the most important figure to take.

        So working on that figure, my 25mm or 1" siphon stand pipe will work up to 1400 ~ 1600 lt/hr flow. You need a bigger stand pipe.

        I would recommend a 2 inch stand pipe with 3" to 2" reducer or bigger, but don't exceed 1:2 ratio, if cannot get reducer you can flare it top to make a trumpet like shape funnel it will work.

        Bell size must be able to take the widest part of the stand pipe, I recommend for 3" you need at least a 5" PVC pipe.

        Handling that volume of water, you need a good initial vertical from the siphon outlet then an elbow one would do, if you could have 12" of initial vertical as a minimum, it would be great.

        Tuning this siphon to work will be fiddling with this downward vertical and the stand pipe funnel. You can reduce water flow, don't really need that high of a flow rate, but if you do then these are my recommendations.

        Hope this work, this is great, please keep us update. Never done a Mega Siphon before, a very tall ones I did but not Mega.. :)


      14. Thanks for the info. I think then that I will try 2 things.

        1) a single Mega-Siphon for a ll 6 beds using a 2 inch drain with a 4 inch to 2 inch reducer. A 6 inch bell will work for these sizes. I will use an 8 gallon plastic pail with appropriate plumbing as the external housing for the mega siphon (a bit taller than a standard 5 gallon).

        2) If that doesn't work I will use two Mega-Siphons, one each for three IBC growbeds. I will use 1 inch standpipe and drains with a 2 inch to 1 inch reducer and a 4 inch bell. These to be constructed externally using a bucket as well (much cheaper than assembling the housingout of larger PVC fittings!).

        Ideally I would like the two separate systems to be a 1.5 inch drain and standpipe with a 3 inch to 1.5 inch reducer and a 5 inch bell, but alas, 5 inch PVC is not a standard size here in the US and I cannot find it. If there were another product or object that could be easily found to use I am open to suggestions. I'll let you know how it went after I experiement on Saturday.

        Thanks again!!

      15. Selamat Datang Affnan

        I am a newbie .Thanks for a great informative site.
        A 30 liter growbed and 60liter fish tank.Will a bell siphon work .Also what size pipes should I start with.Or will a timer work easier on such a small system

        1. That's a very small system, a siphon will work but require more maintenance due to its small size. 20mm stand pipe siphon are recommended for small set, smaller than this will be very difficult to get right.

          Timer system is easier on this size.

      16. Hi Solarit, thats a small unit. I would recommend a 20mm standpipe bell siphon. But this size you need to do more maintenance since its small root can out do it.

      17. Hi Affnan,

        I am impressed with your knowledge of autosiphon systems. Could you help me design one for my growbed which is 25 ft in length, 2 ft in width and 1 ft depth. Please also tell me the best location in the growbed to place this autosiphon.

        1. Apologise for a very late reply, Siphon is best to be at centre of growbed so that water outflow will be even. However I do not recommend a growbed for Aquaponics to be 25ft in length, its best to split it in 2 minimum or 3, then its more manageable with one siphon at each segment.

          You can use the standard 1" stand pipe siphon for your installation.

      18. Hi Affnan,

        Thank you for great information! I have a question... My siphon will have to travel about 6 to 10 feet (2+ meters) horizontally before reaching my sump. I can easily do the elbow design 6 inches under the growbed, but I see in your diagram the horizontal pipe is 4-6 inches long after the elbow and before the air intake. Would there be any problems if instead of 4-6 inches that was 6-10 feet?

        Thank you!

        1. For such a long return travel its advisable to put a "T" breather on that 6~10 ft run near the growbed. Its just a T on the 6 ft line with a vertical air breather. This is widely use on various setup if using siphon over a very long return.

      19. Thank you for the information. Keep it up

      20. excellent site ! thank mate :)

      21. I appreciate all these drawings as they really make it easier to understand what is happening with the set-up. I didn't understand the loop until you made the drawings.

        I've followed your blog on and off for over a year and yours is one of the best aquaponics blogs I've seen...or at least I can say it is the one most influential for me. Some day I'd like to set up a system like yours, except that we'd need to worry about things freezing in the winter.

        1. Appreciate your comments, I try to make drawings and explanation as simple as I could, English is not my native language its a bit difficult.

          Currently I am not active since as my last few post, situation no right yet, I'll be active again in few months time once all my problem ironed out.

      22. Great website! I live and teach at an International School in Kuala Lumpur, and I would like to aquaponics or hydroponics as a class project with my students. Could you please contact me so that we could discuss some options? I am trying to determine a budget for this type of project and find out where I can buy the materials.
        Thank you,

        1. Hi Aaron, Contacted you via Google+

        2. For school Project check this out :

      23. Why a bell siphon is needed instead of a simple overflow standpipe with a little hole to drain water out and a timed pump ?

        Thanks !

      24. As I get closer and closer to beginning construction of my kitchen-window setup, I'm nailing down details and every recommendation about siphons leads here in the end. People out there really respect your work and openness in sharing it! Thank you!

        I have a question of my own, as well - I hope that's OK :D

        Here are a few images showing the setup I'm thinking about right now...

        The grow bed is 44x44x12 inside, will always have ~2" water at the bottom, and the ebb/flow zone will be 8". The fish tanks up-top are where I'm going to raise some crayfish and some cherry shrimp (well, I'll try) in addition to in the main fish tank, along with water lettuce or water hyacinth for filtration.

        My pump is adjustable, and I'm expecting ~125-200 GPH (~500-800LPH)with the head/pipe run I'm using, but won't know exactly until I start things up with pipe attached (I'll be reducing with 1/2", from 1" out at the pump, because the pump I picked up has room to grow if I add another bed higher up later).

        In my grow bed, (taking into account the space media takes up) will be draining ~25 gallons (~100L) of water each cycle. I'm expecting 4-6 cycles/hour.

        Am I figuring things out in a reasonable way - or am I way off the mark? Which siphon size should I start with for the best chance of only needing minor adjustments (not having to drill a brand new hole - especially a smaller hole! ;) ).

        Thank you again, for any advice you can provide.


      25. Salam Bro Affnan,

        I consider you as one of the aquaponics-Guru of Malaysia and this is an excellent blog for its well documented experiments and articles in aquaponics.

        I'm one of the very-proud Malaysians to note that the had also referred to your idea to put the reducer on top of the standpipe as the first used or probably first written about in their "Japan Aquaponics DIY Aquaponics Guides: Autosiphons - Bell Siphons & Loop Siphons". Congratulations!

        FYI I'm in the middle of setting up my own mini version of aquaponics set using some of your ideas and designs. I hope your bell siphon will work well with a shallow 1.5(L)x1.0(W)x0.3m(H) fish tank. I'm thinking of an alternate flush siphon from two growbeds for the water level in the fish tank to be at least 3/4 of its maximum volume. Do you think that this ratio is achievable?

        Thank you in advance for the advice. Hope to hear from you soon and your new aquaponics set.


        1. That fish tank will hold at least 100 US Gallon, and with 2 growbed it should take 15% of that 100 gallon each, 2 growbed will take maximum 30% water from tank. Its achievable with 2 growbed.

          My new setup will use 2 GB of the one that I normally use and with same almost same size tank you use.

      26. Would adding a snorkel to help break the siphon be a helpful thing to do?

        1. My design don't need the snorkel. If you are using a stand pipe without the funnel part on top I believe you will need it.

      27. Is there a ratio between the size of the fish tank and the grow tank? Is there any way to figure out how many fish and what size of fish are needed to make sure there is plenty of waste for the plants to remain healthy?
        Just trying to start off in this endeavor and am lost in how to determine this.

        1. For size of fish tank to growbed I reccommend check :

          Number of fish will depend on size of fish tank, you can start with 1 lb of fish with every 1 gallon of water, this is at its maximum. On average I would put 1 fish to each gallon of water as mentioned above this is the extreme. Bigger fish needs more volume, some practice 1 fish every 4 gallon, this is the opposite of the scale. You have to figure out something in between for your system

      28. Hello I'm new to all of this, so first I would like ti thank you for all the great info you have given us all. I am trying to start a small grow bed (GB) in my bay window of my sun room. 3' x 1.5' x 8" I want to plant flowers in this for my wife. Feeding the grow bed I have a 20 gallon with 7 Chichlid in it. I was wondering if I could use a bell siphon on this with the depth being so low? (I would probably want my water level high mark around 6") should I try another means of siphoning the bed out? Also would one fill and drain a hour be enough for this I will be trickleing water down to the bed through cut wine bottles that will also have media and flowers in it. Any helo would be a big helo

      29. PVC fitting tools has specific gravity of 1.2 and a tensile strength of 2000 psi.