This part of ISO 17769 specifies terms, letter symbols and units related to the flow of liquids through rotodynamic and positive displacement liquid pumps and associated installations. It serves as a means of clarifying communications between the installation designer, manufacturer, operator and plant constructor. This part of ISO 17769 identifies the units in common usage, but all additional legal units can be used.This part of ISO 17769 deals mainly with pumping systems.NOTE 1 For ease of use, some definitions already available in ISO 17769-1 are repeated.This part of ISO 17769 is not concerned with terms, letter symbols and units referring to the component parts of rotodynamic and positive displacement pumps and installations. Whenever possible, symbols and definitions conform to those used in ISO 80000-1, with further explanations where these are deemed appropriate. Some deviations have been incorporated for reasons of consistency. NOTE 2 In addition to terms used in the three official ISO languages (English, French and Russian), this document gives the equivalent terms in German; these are published under the responsibility of the member bodies for France (AFNOR), Russia (GOST R) and Germany (DIN), and are given for information only. Only the terms and definitions given in the official languages can be considered as ISO terms and definitions.