Physical evidence for the use of siphons by Greeks are the Justice cup of Pythagoras in Samos in the 6th century BC and usage by Greek engineers in the 3rd century BC at Pergamon. Pascal's siphon, showing two beakers of mercury inside a container of water, demonstrating that a siphon works by atmospheric pressure, not that "nature abhors a vacuum"Įgyptian reliefs from 1500 BC depict siphons used to extract liquids from large storage jars. But the cohesion tension with gravity theory cannot explain CO 2 gas siphons, siphons working despite bubbles, and the flying droplet siphon, where gases do not exert significant pulling forces, and liquids not in contact cannot exert a cohesive tension force.Īll known published theories in modern times recognize Bernoulli’s equation as a decent approximation to idealized, friction-free siphon operation. The atmospheric pressure with gravity theory obviously cannot explain siphons in vacuum, where there is no significant atmospheric pressure. It need not be one theory or the other that is correct, but rather both theories may be correct in different circumstances of ambient pressure. Consequently, the cohesion tension theory of siphon operation has been advocated, where the liquid is pulled over the siphon in a way similar to the chain fountain. ![]() However, it has been demonstrated that siphons can operate in a vacuum and to heights exceeding the barometric height of the liquid. Then atmospheric pressure was able to push the liquid from the upper reservoir, up into the reduced pressure at the top of the siphon, like in a barometer or drinking straw, and then over. The traditional theory for centuries was that gravity pulling the liquid down on the exit side of the siphon resulted in reduced pressure at the top of the siphon. There are two leading theories about how siphons cause liquid to flow uphill, against gravity, without being pumped, and powered only by gravity. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, above the surface of a reservoir, with no pump, but powered by the fall of the liquid as it flows down the tube under the pull of gravity, then discharging at a level lower than the surface of the reservoir from which it came. It also demonstrates that the effect of atmospheric pressure at the entrance is not canceled by the equal atmospheric pressure at the exit.Ī siphon (from Ancient Greek: σίφων, romanized: síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. ![]() In the flying-droplet siphon, surface tension pulls the stream of liquid into separate droplets inside of a sealed air-filled chamber, preventing the liquid going down from having contact with the liquid going up, and thereby preventing liquid tensile strength from pulling the liquid up.
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