This European Standard deals with 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. The standard identifies the units in common usage but all further legal units may be used. A definition of a liquid pump is included. This standard deals solely with conditions described by positive values for the rate of flow and pump h head.