Which statement best describes a positive displacement pump?

• A. They typically have high capacities and are used for large volumes.
• B. They cannot handle abrasives and crystallizing liquids and must not run dry.
• C. They use centrifugal force to pump liquids.
• D. They are only used in industrial applications.

Answer: (B)

The statement that a positive displacement pump cannot handle abrasives and crystallizing liquids and must not run dry accurately characterizes the limitations and operational requirements of this type of pump. Positive displacement pumps work by trapping a fixed amount of liquid and forcing it through the discharge. This design makes them excellent for moving viscous liquids and providing a consistent flow at varying pressure levels.

However, running dry can lead to severe damage because the pump relies on the fluid for lubrication and cooling. Without the fluid, the moving parts may experience excessive friction, leading to wear and potential failure. Additionally, when pumping abrasives or materials that can crystallize, the wear on the pump components can be significant. These factors necessitate careful consideration and limitation when selecting a positive displacement pump for certain applications. This understanding is crucial for ensuring equipment longevity and proper system function.