Which of the following compressors is classified as not being a positive displacement type?

The centrifugal compressor is classified as a non-positive displacement type because it operates by converting kinetic energy into pressure energy through the use of a rotating impeller. As air flows through the impeller, it gains velocity and subsequently, when directed into a diffuser or volute, this velocity is transformed into increased pressure. This process creates a continuous flow of gas, meaning that the compressor doesn’t store a finite volume of air or fluids in a chamber, which is a key characteristic of positive displacement compressors.

In contrast, positive displacement compressors, such as scroll, screw, and rotary compressors, function by trapping a fixed volume of gas and then compressing it into a smaller volume, effectively increasing the pressure. These compressors work on the principle of reducing the volume of a confined space, leading to the compression of the gas.

Understanding the distinction between these types of compressors is essential for applications where pressure, efficiency, and continuous flow of air or gas are critical, such as in respiratory equipment used by first responders.