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Airlock Between Water and Air

  1. Apr 18, 2016 #1

    I have searched and searched but cannot seem to find an apparatus to solve my problem.

    For this project (see attachment for the drawing) I need to be able to drop a steel ball into a tube in position A and have to go into the side of the water tank and fall to the bottom of the tank without losing water. This project can not use any type of energy to make it function so I am wondering if there is some type of airlock or water lock process/device I can use. Any ideas would be appreciated.

    Attached Files:

    • tank.jpg
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  2. jcsd
  3. Apr 18, 2016 #2


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    You'll have to keep the opening of the tube on the outside of the tank higher than the water level inside the tank, otherwise you'll get a wet floor.
  4. Apr 18, 2016 #3


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    How far up the tube BA is water permitted to fill? If you must prevent entry of water at point B you are going to have problems.
    You could use two large ball valves near A in the tube, with room between them for the steel ball(s).
    Close the lower valve, open the upper valve. Drop in the ball. Close the top valve then open the bottom valve to release the ball.
  5. Apr 19, 2016 #4
    Thanks for the comment Baluncore! Water can fill the tube completely. I had considered a two door system like you are referring to but could not find such a device available for purchase. I did forget to mention one important thing which is the valves would need to be able to be opened by the weight of the ball so no human intervention to operate the valves. I was thinking that some type of spring activated valve tuned to open with the weight of the ball and then would close after the ball passed through. Again, I'm not sure if there is anything like this on the market or if it would need to be fabricated.
  6. Apr 19, 2016 #5


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    This sounds like an attempted perpetual motion machine. What you describe is probably not possible.
  7. Apr 19, 2016 #6


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    Then you really have little choice but to extend the tube at A to a level above the water level in the tank. Why can you not do that ?

    What drops the balls into the tube ?

    In order to operate a gate or valve, the weight of the ball would need to overcome the hydrostatic pressure difference between the tube and the tank. You might partially cancel that pressure by using a spring or counter-balance, but there is not much energy available to operate the gate seals.
    How deep is the tank ?
    How long is the tube ?
    What is the ball diameter ?
  8. Apr 19, 2016 #7


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    This cannot be classed as an impossible "perpetual motion machine" without some magic way of closing the cycle by returning the balls to the top of the tube. Hence my question "What drops the balls into the tube ? ".
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