What is a common characteristic of positive displacement pumps?

• A. They are always electric powered
• B. They can only handle light fluids
• C. They can maintain constant flow against system pressure
• D. They have a single piston type

Answer: (C)

Positive displacement pumps are characterized by their ability to move a specific volume of fluid with each cycle of operation, regardless of the system pressure downstream. This allows them to maintain a constant flow rate even in the presence of varying pressure conditions, which is a fundamental aspect of how they function. As the pump mechanism operates—whether through gears, vanes, or pistons—it displaces a set volume of fluid on each stroke or rotation. This consistent volumetric flow is critical for applications requiring precise dosing or steady flow.

The other options provided do not accurately reflect the nature of positive displacement pumps. For instance, while some positive displacement pumps can indeed be electric powered, they can also operate using other forms of energy, such as hydraulic or pneumatic systems. Furthermore, these pumps are not limited to handling only light fluids; they can be designed to handle a wide range of viscosities and fluid types, making them versatile in various applications. Lastly, while some types of positive displacement pumps use a single piston, many types exist, including gear pumps and diaphragm pumps, each with different configurations and mechanisms, so it is not accurate to say they are all defined by a single-piston type.