Definitions. Characteristic quantities
Volumetric pumps for fluids

Reference plane: plane from which the various heights are measured, whether geometric, manometric, practical, suction, load, discharge, etc., as well as the NPSH.

In the case of a horizontal axis pump (figure 1a ), the reference plane is the horizontal plane passing through the axis of rotation. In the case of a pump with a vertical axis (figure 1b ), the reference plane is the horizontal plane passing through the highest point of the active parts.

Geometric suction height h_a (figure 2): vertical distance separating the liquid level at suction from the reference plane.