Which type has an impeller?

• A. centrifugal
• B. positive displacement
• C. axial flow
• D. gear

Answer: (A)

The impeller is the rotating component that adds energy to the fluid. In a centrifugal pump, the impeller is the main energy-adding element. As it spins, fluid enters near the center and is hurled outward by the blades, increasing velocity and pressure so it can be discharged through the pump. Positive-displacement pumps move a fixed amount of fluid per cycle using pistons, diaphragms, or gears, and they don’t rely on an impeller to move the liquid. Gear pumps use meshing gears to trap and push fluid, also without an impeller. Axial-flow pumps do have an impeller (propeller-like) and move fluid along the axis, but for this question the example most directly associated with using an impeller to impart energy is centrifugal.