Which characteristic of dynamic pumps distinguishes them from positive displacement pumps?

Dynamic pumps are characterized by how they move fluid. One key distinction between dynamic pumps and positive displacement pumps is that the pressure generated by dynamic pumps varies with system resistance. This means that the flow rate can change in response to varying conditions in the system. When resistance increases (for instance, due to a blockage or increase in flow demand), the pressure in a dynamic pump will drop, thus affecting the flow rate.

Dynamic pumps typically utilize kinetic energy imparted by the pump's impeller, which accelerates the fluid and converts this kinetic energy into flow. In contrast, positive displacement pumps move fluid by trapping a fixed volume and then forcing it into the discharge line, maintaining a constant flow rate regardless of the pressure in the system. This fundamental operational difference is crucial for understanding how each type of pump reacts under different conditions and influences system design and performance.

While constant flow rate and variable flow rate describe operational aspects of pumps, they don't distinctly illustrate the characteristics unique to dynamic pumps versus positive displacement pumps. The requirement for external lubrication might pertain to maintenance considerations but does not define the operational mechanics of either pump type.