What are the two main categories of positive displacement pumps and compressors?

The two main categories of positive displacement pumps and compressors are reciprocating and rotary.

Reciprocating pumps and compressors use a back-and-forth motion to displace fluids or gas, which allows for a high level of pressure to be generated. This type is commonly found in applications requiring precise flow measurements and high pressures. An example of this is a piston pump, which utilizes a piston that moves within a cylinder to create an increase in pressure and move the fluid.

On the other hand, rotary pumps and compressors operate using rotational motion. They displace fluids or gases by means of rotating elements, such as gears, vanes, or screws. This design typically allows for a continuous flow of the substance being moved, making rotary systems efficient for handling larger volumes at lower pressures. Gear pumps and screw compressors exemplify rotary devices and are often utilized in applications where smooth and continuous flow is crucial.

The other options present various types of pumps or categories that do not represent the fundamental classifications of positive displacement systems. Centrifugal pumps, for instance, are a separate category generally classified as dynamic or non-positive displacement pumps, while diaphragm and gear refer to specific types of pumps rather than overarching categories. Pneumatic and hydraulic refer to systems that use air and liquid