The Venturi effect is named after its discoverer, the 18th-century Italian physicist Giovanni Battista Venturi. The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. Video of a Venturi meter used in a lab experiment Idealized flow in a Venturi tube The meter is "read" as a differential pressure head in cm or inches of water.
A flow of air through a Pitot tube Venturi meter, showing the columns connected in a manometer and partially filled with water. Reduced pressure caused by a flow restriction in a tube or pipe The static pressure in the first measuring tube (1) is higher than at the second (2), and the fluid speed at "1" is lower than at "2", because the cross-sectional area at "1" is greater than at "2".