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Misc. Hydrostatics problem in a water vessel

  1. Feb 13, 2019 at 8:03 PM #1
    I am trying to design a water vessel system that maintains it's water level as it is consumed.

    In item 1. It's a simple water barometer, where the height of water in the column can be supported by atmospheric pressure until 10.34.

    In item 2. There are two columns that are open to atmosphere that are higher than the top of X reservoir (accordion-style that can be compressed down to create a U shaped vessel). Water will be sucked out of the side columns. What force would I need to apply to the top of that vessel to maintain the water level at the very top of the column.

    I tried Patm=F/A on the X reservoir, but that seems really high. I am having a hard time modelling this. My goal is the smallest force possible to maintain the height of water.

    Any help would be much appreciated.

    Attached Files:

  2. jcsd
  3. Feb 14, 2019 at 3:50 AM #2


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    I'm not clear what your question is, but item 1 seems to do what you want.

    This is the traditional water feeder for poultry, though the central tank is usually much larger (in diameter.) As the water level at the edges falls, air leaks into the central column and allows water to leak into the side trough. So the level in the side trough always remains close to the bottom edge of the central tank.

    Larger troughs use float valves to control the supply from a reservoir (such as a water main!)

    Both have the advantage over your 2nd item, that the energy to control the level comes from the stored energy in the water reservoir. So no need for additional mechanism (& PSU) to apply force to your bellows.

    Item 1 can also be modified to restrict the inflow of water, to avoid overshoot, and to use a small bleed tube from the top of the reservoir as a level sensor to give a finer response and to more accurately specify the position at which the level is measured.
  4. Feb 15, 2019 at 2:26 AM #3
    Thanks for the advice. Your feedback was exactly what I was looking for.
  5. Feb 15, 2019 at 2:30 AM #4
    I don't actually know what you mean by your last paragraph. How would you would the small bleed tube operate as a level sensor? Can you please explain how something like that might work?
  6. Feb 15, 2019 at 2:55 AM #5
    I believe that this would be a passage exclusively for the air to enter the reservoir.

    In a traditional chicken water feeder, the gap that forms when the water level in the trough drops allows air into the reservoir, and water out of the reservoir. This usually happens in "glugs", as the air and water is passing each other through the same hole.

    If you add a narrow gauge tube which connects to the top of the reservoir (where the air is) and connects to the trough at the level the water needs to be, when the water level drops, air will be sucked up the tube and water will flow out of the bottom. once the water level in the trough has increased to cover the tube, it will start sucking up water, which will stop the refill. this would allow the water to flow out more smoothly.

    For a comparison, fill a glass (or rigid plastic) bottle with water, and pour it out quickly - it glugs out, as the air and water have to share the same aperture. refill the bottle and pour it out slowly, so that there is always an air gap over the water flowing out of the mouth of the bottle, and the water pours out in a smooth, controlled manner.

    The bleed tube will also allow the connection between the trough and the reservoir to be kept below the water level, rather than being used to dictate it.
  7. Feb 15, 2019 at 4:03 AM #6


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    Exactly. Better than I'd have explained it!
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