The classic venturi tube pioneered by Clemens Herschel in 1887 has been adapted in a variety
of forms broadly classified as flow tubes. All flow tubes work on the same principle: developing a
differential pressure by channeling fluid flow from a wide tube to a narrow tube. The differ from the
classic venturi only in construction details, the most significant detail being a significantly shorter
length than the classic venturi tube. Examples of flow tube designs include the Dall tube, Lo-Loss
flow tube, Gentile or Bethlehem flow tube, and the B.I.F. Universal Venturi.
Another variation on the venturi theme is called a flow nozzle, designed to be clamped between
the faces of two pipe flanges in a manner similar to an orifice plate. The goal here is to achieve
simplicity of installation approximating that of an orifice plate while improving performance (less
permanent pressure loss) over orifice plates: