With increasing flow through a constriction, turbulence occurs which can lead to inaccuracies. Venturi tubes with conical constrictions are used to reduce these disturbances as far as possible. The Venturi nozzle (flow nozzle) consists of a converging section with a rounded profile and cylindrical neck and, at higher temperature and flow rates, provides greater strength and dimensional stability than an orifice. This variant of flow meters is particularly suitable for steam, chemical substances, gases and other media, even with high process temperatures. The accuracy corresponds to ≤ ±0.1 % of the actual flow volume and the repeatability of the measurement is 0.1%. Process media with extremely low or very high Reynolds numbers of up to several million are no problem for these highly robust flow meters. The simple design allows for an enduring operation with low maintenance costs.