What characterizes positive displacement pumps?

Positive displacement pumps are characterized by their ability to deliver a constant flow rate regardless of the system pressure, as long as the pump speed remains constant. This means that the output flow of these pumps primarily depends on the geometry of the pump and the rotational speed of its components, rather than the characteristics of the fluid or external power inputs.

In different conditions, such as changes in pressure, positive displacement pumps still maintain their flow rate, making them consistent and reliable in various applications. This is in contrast to other types of pumps, where the output can fluctuate based on system demands and fluid properties.

The other options present different contexts or limitations not applicable to positive displacement pumps, which solidifies the choice of the option that emphasizes their constant flow rate feature.