Long radius nozzle is a flow throttling device with elliptical inlet and cylindrical outlet. There are two nozzle designs with different shape of elliptical arc limiting their tapered inlet:

• Nozzle with large diameter ratio, applicable within 0.25 ≤ β ≤ 0.8
• Nozzle with small diameter ratio, applicable within 0.2 ≤ β ≤ 0.5

In most cases the nozzle body is welded into piping, it is so-called weld-in design or, it is embedded between the flanges. Weld-in design of the nozzle consists of straight lengths of piping downstream the nozzle. Weld-in embedding into piping has the advantages such as material savings on the flanges and subsequently minimized leakage in the flanged joint. Placement of the nozzle between the flanges is recommended up to PN 100.

Axis of differential pressure tapping (+) is in the distance of 1D from the inlet side of the nozzle. Axis of differential pressure tapping (-) is in the distance of 0.5D from the inlet side of the nozzle except for nozzle with small diameter ratios β ≤ 0.3188, for which the axis of back tapping has to be within the distance 1.6d from the inlet part of the nozzle, where d symbolizes diameter of throttling throat of the nozzle. Upon agreement with the customers outlets of differential pressure are always customized to various options of primary element attachment to the measuring circuit.

ISO 5167-3 standard defines possibility to use long radius nozzle for piping diameters from 50 mm up to 630 mm. For the production of long radius nozzles there are mostly used combinations of standard carbon steel and stainless steels for the measurement of fluid flow and refractory steels for measurement of steam flow, e.g. alloyed steels 14MoV6-3/15 128, 10CrMo9-10/11CrMo910, 13CrMo4-5, 16Mo3, X10CrMoVNb9-1 and 15NiCuMoNb5.

Long radius nozzle is manufactured as a working meter.

Long radius nozzle has a great advantage of high operational reliability and applicability in measurement of fluid, gas and steam flows, including fluids with high working pressure or highly superheated steam. There is another advantage: stability of coefficient of flow C in Re_D from 10⁴ to 10⁷.

Long radius nozzles are especially applicable for high pressure parts of boiler systems and distribution (high pressure steam, feed water).

Long radius nozzle can be incorporated both in vertical and horizontal piping.