Which of the following is a true statement about positive displacement pumps?

• A. They only pump water in one direction
• B. They are inefficient compared to centrifugal pumps
• C. Some can pump water on both forward and return strokes
• D. They consist exclusively of rotary gear types

Answer: (C)

Positive displacement pumps operate by trapping a fixed amount of fluid and forcing it into the discharge pipe. This principle allows for the capability to create a consistent flow, regardless of external conditions such as pressure variations.

The statement highlighting that some positive displacement pumps can pump water on both the forward and return strokes is accurate. This is especially common in types of displacement pumps such as diaphragm or piston pumps. These designs enable the pump to push fluid during both strokes, which can be beneficial in various applications, including those requiring precise volume control and continuous flow in either direction.

This specific characteristic emphasizes the versatility of positive displacement pumps, distinguishing them from centrifugal pumps that typically only move fluids in one direction and depend on the kinetic energy imparted by a rotating impeller. Understanding this functionality can be crucial for applications requiring reversible flow or specific operational requirements.