What type of pump is a positive displacement pump?

A positive displacement pump operates by trapping a fixed amount of fluid and then forcing (or displacing) that volume into the discharge pipe. This characteristic distinguishes it from other types of pumps, as it maintains a constant flow rate regardless of the pressure conditions in the system.

The roller pump functions by using rollers to compress a flexible tubing, effectively creating a chamber that traps and displaces the fluid. This mechanism ensures a steady and precise flow of the fluid with minimal turbulence. This is why the roller pump is classified as a positive displacement pump.

In contrast, other types of pumps mentioned do not operate on the principle of displacing a fixed volume. For instance, centrifugal pumps rely on kinetic energy to move fluids, and their flow rate can vary with pressure changes. Similarly, blowers generally move air by creating a pressure difference but do not displace a fixed volume in the same manner. Screw pumps, while they do have some characteristics of positive displacement, operate by using rotating screws to move fluid and may not always offer the same precision as roller pumps.

Overall, the roller pump's mechanism of action aligns directly with the definition of positive displacement pumps, making it the correct answer.