Part 2 of ISO 5167 covers the most widely used differential pressure device of all, the orifice plate. It specifies the geometry and methods of use as well as performance coefficients and uncertainty expectations in detail. The orifice plate is an extremely well understood differential pressure generator and has been documented for over hundreds of years.
The general shape, flatness, surface finish, bore and square edge requirements of an orifice plate are described in detail. Options for the differential pressure tapping locations are illustrated including D & D/2, corner taps and the more traditional flange taps in addition to the quality of tapping hole required to produce a reliable measurement.
The limitations of plates are listed along with corresponding uncertainty expectations for uncalibrated devices with equations to predict permanent pressure loss.
An extensive section is dedicated to the installation requirements of orifice plates with detailed information on the upstream and downstream straight lengths required for differing inlet piping configurations which have been generated from empirical data. Flow conditioners and flow straightener designs are considered and demonstrate, with worked examples, how straight lengths can be reduced when installed as part of the meter assembly.
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.
