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An experiment with a glass funnel showing the action of vacuum on the ball caused by blowing the air downwards through the funnel's stem. It is a demonstration of a relation between dynamic and static pressure, i.e. Bernoulli's principle. The ball falls of the funnel. But, when blowing, the dynamic pressure increases. According to the Bernoulli's principle, in this case the static pressure between the ball and the walls of the funnel decreases, the ball is sucked by this low pressure and prevents it from falling.

Suction is the flow of a fluid into a partial vacuum, or region of low pressure.[1] The pressure gradient between this region and the ambient pressure will propel matter toward the low pressure area. Dust is sucked into a vacuum cleaner when it is pushed in by the higher pressure air on the outside of the cleaner.

This is similar to what happens when humans breathe or drink through a straw. Both breathing and using a straw involve contracting the diaphragm and muscles around the rib cage. The increased volume in the chest cavity or thoracic cavity decreases the pressure inside, creating an imbalance with the ambient air pressure, or atmospheric pressure. This imbalance results in air pushing into the lungs or liquid pushing up through a straw and into the mouth.


Pumps typically have an inlet where the fluid (or air) enters the pump and an outlet where the fluid/air comes out. The inlet location is said to be at the suction side of the pump. The outlet location is said to be at the discharge side of the pump. Operation of the pump creates suction (a lower pressure) at the suction side so that fluid/air can enter the pump through the inlet. Pump operation also causes higher pressure at the discharge side by forcing the fluid/air out at the outlet. There may be pressure sensing devices at the pump's suction and/or discharge sides which control the operation of the pump. For example, if the suction pressure of a centrifugal pump is too high, a device may trigger the fluid pump to shut off to keep it from running dry; i. e. with no fluid entering.

Under normal conditions of atmospheric pressure suction can draw pure water up to a maximum height of approximately 10.3 m (33.9 feet).[2]

In medicine, suction devices are used to clear airways of materials that would like to impede breathing or cause infections, to aid in surgery, and for other purposes.

See also[edit]


  1. ^ (LL.D.), Alexander JAMIESON (1827). A Dictionary of Mechanical Science, Arts, Manufactures and Miscellaneous Knowledge.
  2. ^ Calvert, James B. (11 May 2000), "Maximum height to which water can be raised by a suction pump", Hydrostatics