![]() However, the cohesion model predicts that if cavitation can be prevented, the barometric height limit can be broken. the water starts to boil thereby breaking the column. In the cohesion model, the limit is explained by the pressure at the top of the siphon falling below the vapour pressure of water, at the given temperature, so that cavitation occurs, i.e. ![]() In the case of the atmospheric model, the pressure of the atmosphere is required to hold the column of water together. Evidence in support of the gravity cohesion model is that siphons have been shown to operate under vacuum conditions 7, 8, 9 and the model can explain a curious waterfall-like feature when a siphon is operating close to the barometric limit 10.īoth siphon models–atmospheric and cohesion–predict that the maximum height of a siphon is dependent on the ambient barometric pressure. Another piece of evidence in support of the atmospheric model is the fact that siphon flow can occur with an air bubble inside the tube so that there is no physical connection between the water molecules. In this model, a siphon is considered to be two back-to-back barometers. Key evidence for the atmospheric model is that the maximum height of a siphon is approximately equal to the height of a column of liquid that can be supported by the ambient barometric pressure. Two competing models have been put forward, one in which siphons are considered to operate through gravity and atmospheric pressure and another in which gravity and liquid cohesion are invoked. ![]() Although the siphon has been used since ancient times, the means of operation has been a matter of controversy 1, 2, 3, 4, 5, 6.
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