What type of pump uses closely meshed gears, vanes, or lobes rotating within a close-fitting chamber?

The type of pump that uses closely meshed gears, vanes, or lobes rotating within a close-fitting chamber is a rotary pump. Rotary pumps operate by the movement of these components to create a vacuum that draws fluid into the chamber and then pushes it out, allowing for a continuous flow of liquid. The design ensures that the fluid is moved in a steady, controlled manner, making rotary pumps particularly effective for applications where high viscosity fluids or precise flow rates are required.

Positive displacement pumps also create flow through a fixed volume mechanism but they do so using different operational principles that can include reciprocating or rotary motions. Axial flow pumps, on the other hand, work by moving fluid in a direction parallel to the pump shaft, typically using an impeller but not through the mechanisms described in this question. Diaphragm pumps utilize a flexible diaphragm to create pressure, which is distinctly different from the rotary mechanism described.

Thus, the characteristics and function of a rotary pump align closely with the use of gears, vanes, or lobes in a close-fitting chamber, making it the correct answer in the context of the question.