Part 3 of ISO 5167 currently covers two types of standard nozzle, the 1932 ISA nozzle and the long radius nozzle as well as the Venturi nozzle which has the same upstream face as the 1932 nozzle but includes a divergent section similar to that of a conventional Venturi device.
The general shape, nozzle profile, surface finish and bore requirements of nozzles are described in detail. The differential pressure tapping locations are illustrated for each of the devices as well as the quality of tapping hole required to produce a reliable measurement.
The limitations of nozzles are listed along with corresponding uncertainty expectations for uncalibrated devices with equations to predict permanent pressure loss. The Venturi nozzle has a lower pressure loss than the standard equivalent nozzle. Flow through the measurement section is assumed to remain subsonic in all cases.
An extensive section is dedicated to the installation requirements of nozzles with detailed information on the upstream and downstream straight lengths required for differing inlet piping configurations all of which have been generated from empirical data.
ISO working group efforts are currently underway to include a throat tapped nozzle section to Part 3 of the standard. This work is nearing completion and is expected to be published in 2019. Solartron ISA have been active participants for over 15 years in the ISO/TC 30/SC2 technical committee assigned to ISO 5167. The standard is due for ISO systematic review in 2019.
