This is a strange question for me because this is so extremely common, but I have never heard a name to describe exactly what it is.

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This is commonly used to provide water to animals from a trough or tube at a constant water level without dripping. As the water in the trough is reduced in height from drinking, air bubbles enter the reservoir which then releases sufficient water from the container to refill the trough and stop further air from entering the container.

The remaining liquid is held inside the container by the vacuum above the water, and atmospheric pressure holding the water up in the evacuated space, even though the bottom remains open.

And this reservoir container is formally called a.... ?

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    $\begingroup$ To be accurate the drawing should have on open end on the cylinder. $\endgroup$
    – paparazzo
    Apr 10, 2018 at 18:32
  • $\begingroup$ Can you provide any references for where this is "commonly used"? Intuitively, I'd imagine it being difficult to evacuate the air, particularly if lifting a large body of water, without an expensive and power-hungry pump? Stock Watering Tanks that I've seen typically use a ball/float valve to control flow from the reservoir, meaning the tank can be filled at atmospheric pressure: polymaster.com.au/catalogue/agriculture/stock-troughs/… What you're describing is commonly used as a "Fish observation tower", however. $\endgroup$ Jul 9, 2018 at 7:34
  • $\begingroup$ It has been used for providing water for chickens on small rural farms for at least 100 years, probably much longer. Random web example: amazon.com/Little-Giant-Poultry-Waterer-7906/dp/B004L62JF8 $\endgroup$ Jul 9, 2018 at 15:17

2 Answers 2


A Torricelli vacuum, and barometers with mercury apply the same principle.


Some people refer to this arrangement as a bubbler. You will also see it referred to as a watering tube.


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