Communicating vessels

Communicating vessels : it is the name given to a set of containers communicated at the bottom and containing a homogeneous liquid ; it is observed that when the liquid is at rest it reaches the same level in all the containers, without influencing the shape and volume of these.



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  • 1 The principle of the communicating vessels
  • 2 Operation
  • 3 Applications of the communicating vessels
  • 4 Source
  • 5 See also

The principle of the communicating vessels

If there are two connected containers and a liquid is poured into one of them, it will be distributed between them in such a way that, regardless of their capacities, the level of liquid in each container is the same. This is the so-called communicating vessels principle, which is a consequence of the fundamental equation of hydrostatics .

If two points A and B are taken located at the same level, their hydrostatic pressures must be the same, that is: then if pA = pB necessarily the heights hA and hB of the respective free surfaces must be identical hA = hB. If two liquids of different densities are used and are not miscible, then the heights will be inversely proportional to the respective densities.

Indeed if pA = pB. This equation allows, from the measurement of the heights, the experimental determination of the relative density of one liquid with respect to another and therefore constitutes a way of measuring non-miscible liquid densities if that of one of them is known.


This is explained because the atmospheric pressure and gravity are constant in each container, therefore the hydrostatic pressure at a given depth is always the same, without influencing its geometry or the type of liquid. Blaise Pascal demonstrated in the seventeenth century , the support that is exerted on a mole of a liquid, is transmitted entirely and with the same intensity in all directions ( Pascal’s Principle). They serve to demonstrate that hydrostatic pressure depends only on height. In this case, it consists of four glass containers of different capacities and forms joined at the bottom by a metal tube that is closed at one end. Pouring the liquid into any one of the glasses shows that it reaches the same height in all of them.


Communication vessel applications

At least since the time of Ancient Rome , they were used to bridge uneven terrain by channeling water with lead pipes . The water will reach the same level at the elevated points of the trough, acting as the communicating vessels, although the maximum depth to save depended on the capacity of the tube to resist pressure .

In cities, drinking water tanks are installed in the highest places, so that the pipes can function as communicating vessels, distributing the water to the highest floors of buildings with sufficient pressure.

The complex fountains of the Baroque period that adorned gardens and cities, used high reservoirs and through pipes as communicating vessels, propelled the water with various fountain systems. The hydraulic presses are based on the same principle and are widely used in various industrial processes.

Municipal facilities often take advantage of this principle of communicating vessels to supply water to homes

This serves to overcome the different levels of water. The locks are used for boats to save differences in level.

The boat enters the lock . This is filled with water to equalize the level with the next lock. From then on, the boat can go to this lock, and so on.

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