Which of the following is NOT a type of rotary positive displacement pump?

A diaphragm pump is not a type of rotary positive displacement pump because it operates differently from the rotary mechanisms. While rotary positive displacement pumps, such as screw, gear, and rotary vane pumps, utilize rotating elements to create a continuous flow by trapping a certain amount of fluid and forcing it through the discharge, a diaphragm pump utilizes a flexible diaphragm that reciprocates to create pressure and move fluid. This distinction in operation means that the diaphragm pump is categorized more accurately as a reciprocating pump rather than a rotary pump. Understanding the different types of pumps and their operating principles is crucial in wastewater management, as it helps to select the appropriate type of pump for specific applications.