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  1. #1
    Junior Member
    Join Date
    Feb 2017
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    1

    Bell siphon outlet under water level

    Hi there,

    I'm planning to make my first growbed including a bell siphon this weekend but have one final question...
    in al the video's and available resources about the bell siphon i found that the water outlet of the bell siphon is always slightly above the tank but in my aquarium i have build inlet/outlet pipes into my rocks (for an filter). So my question is : is it able to have your water outlet pipe into your tank when using a bell siphon.

    Kind regards,

    Max

  2. #2
    Aquaponics 101 Oliver's Avatar
    Join Date
    Mar 2009
    Location
    Show Low, AZ USA
    Posts
    248
    I believe what you are asking, "is it possible to have the outlet pipe (siphon down pipe) from the bell siphon go into the water of your aquarium?". The answer is no.

    You must allow air to enter the bottom of the bell siphon down pipe so it can help to break siphon. Also, if the down pipe from the siphon is in the water it can trap air in it preventing the siphon from filling with water, which will not allow the siphon to start siphoning out the grow bed's water.

    A vacuum is created due to the weight of the down pipe water (the longer the down pipe the better it works), which is greater than the weight of the water in the siphon's bell (for a given cross sectional area). This imbalance of weight (combined with the atmospheric air pressure) creates a pressure difference, and that is what makes the siphon work.

    It is also important not to have too much air in the top of the bell, as it acts as a buffer every time the stand pipe is fully covered with water and a siphon tries to begin. It supplies air breaking the siphon action before it can begin. Having minimal clearance between the top of the stand pipe and the top of the bell (not so little that it restricts the water flow into the stand pipe) keeps the air in that area to a minimum and makes it easier for the bell to create the necessary vacuum to start the siphon working.

    The same rules apply for a loop siphon, the longer outside (of the grow bed) down portion of the loop and the shorter up portion (can be inside or out side of the grow bed) creates the same effect as the bell siphon, without the bell. The water goes over the top of the loop as the grow bed fills and once the down pipe of the loop gets fully covered with water the siphon action begins. Note: there is very little air space in a loop siphon, so it works better than a bell siphon, if otherwise properly designed. The critical part is the portion of the loop as it turns from horizontal to the vertical down pipe. Using a smooth transition reducer right after the downward bend (think Affnan, also thank Affnan) will improve the siphon starting.

    Oliver
    To measure is to know

  3. #3
    Junior Member
    Join Date
    Oct 2017
    Posts
    1
    That's good to know, Oliver. Thanks a lot for the explanation.

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