Siphon

Siphon is a tube in an inverted 'U' shape, which causes a liquid to flow uphill, above the surface of the reservoir, without pumps, powered by the fall of the liquid as it flows down the tube under the pull of gravity, and discharged at a level lower than the surface of the reservoir it came from.

Principle

The siphon works because of the difference in pressure. At the upper reservoir's surface, the pressure is atmospheric pressure minus the liquid's weight above the entry point of the siphon. At the exit of the siphon, the liquid is at atmospheric pressure, because it is open to the air. The lower pressure at the top allows atmospheric pressure on the liquid at the lower reservoir to push the liquid up the tube into the lower pressure zone at the top, and then the greater weight of liquid in the longer leg pushes the liquid up and out the shorter leg to the lower reservoir.

Applications

Siphons are used in a wide variety of applications, from agriculture to the nuclear industry. They are used in irrigation and agriculture for transferring water over a hill. In the nuclear industry, they are used in fuel storage ponds to keep the fuel under water, but allow the water to be drained off in case of a leak.

History

The siphon has been used since ancient times. It was described by Hero of Alexandria in the 1st century AD, and was also used in the Hanging Gardens of Babylon and the Great Pyramid of Giza.

See also

• Hydrostatics
• Fluid dynamics
• Pascal's law

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