Venturi effect

The upstream static pressure (1) is higher than in the constriction (2), and the fluid speed at "1" is lower than at "2", because the cross-sectional area at "1" is greater than at "2". A flow of air through a Venturi meter, showing the columns connected in a manometer and partially filled with water. The meter is "read" as a differential pressure head in cm or inches of water. Video of a Venturi meter used in a lab experiment Idealized flow in a Venturi tube

The Venturi effect is the reduction in fluid pressure that results when a moving fluid speeds up as it is funneled from one section of a pipe to another, smaller section. As the fluid flows into a smaller area, the fluid's velocity increases, while the static pressure decreases. The Venturi effect is an example of Bernoulli's principle.