1. Normative definition

Standard NF X 10 501 defines a positive-displacement pump as follows

Positive-displacement pumps also include gas-injection pumps, which are positive-displacement pumps in which a device enables the injection of an adjustable quantity of a non-condensable gas during the compression phase of the pumping cycle, in order to reduce condensation inside the pump. These pumps are commonly referred to as air ballast or gas ballast pumps.

Volumetric pumps are also classified according...