The Venturi tube is a differential pressure flow meter which, in terms of its geometric dimensions, surface quality, and installation conditions, meets the requirements of the DIN EN ISO 5167-4 standard.
It consists of a narrowing inlet section, followed by a cylindrical section and a conical divergent section called a diffuser. See Fig. 1 Venturi tube
With the same nominal diameter and diameter ratio, the overall pressure losses of the Venturi tube are smaller than with a standard Venturi nozzle.
For a measurement accuracy that is comparable to other differential pressure flow meters, the lengths of the inlet sections are considerably shorter than with a standard Venturi nozzle.
The flow rate is calculated from the measured differential pressure level and the flow coefficient (C) using the formula for differential pressure measuring instruments.