Wastewater New York State Practice Exam

Which type of pump is classified as a positive displacement pump?

1. Centrifugal pump

2. Gear pump

3. Submersible pump

4. Diaphragm pump

The correct answer is: Gear pump

A positive displacement pump operates by trapping a fixed amount of fluid and forcing that volume into the discharge pipe. The gear pump exemplifies this mechanism, where two gears rotate within a casing to draw fluid in and push it out, effectively creating a constant flow regardless of downstream pressure. This characteristic is crucial in applications requiring a consistent flow rate and pressure, such as in wastewater systems. In contrast, centrifugal pumps (often used in wastewater treatment) work differently; they impart velocity to the fluid to create flow rather than displacing a fixed volume. Submersible pumps, while they can be positive displacement types, are typically centrifugal in design for most applications and are used in situations where pumps need to operate underwater. Diaphragm pumps also fall under the category of positive displacement pumps but are distinct from gear pumps in their mechanism of operation, which uses flexible diaphragms to move fluid. Thus, the gear pump is the most clear-cut example of a positive displacement pump among the options provided.