engineering methods used to design a centrifugal fan are the same as those to design a centrifugal compressor, so they can look very similar. For purposes of generalization and definition, it can be said that centrifugal compressors often have density increases greater than 5 percent. Also, they often experience relative fluid velocities above Mach number 0.3 when the working fluid is air or nitrogen. In contrast, fans or blowers are often considered to have density increases of less than five percent and peak relative fluid velocities below Mach 0.3. Squirrel-Cage fan Squirrel-Cage fans are primarily used for ventilation. The flow field within this type of fan has internal recirculations. In comparison, a centrifugal fan is uniform circumferentially. Centrifugal pump Centrifugal compressors are also similar to centrifugal pumps of the style shown in the adjacent figures. The key difference between such compressors and pumps is that the compressor working fluid is a gas (compressible) and the pump working fluid is liquid (incompressible). Again, the engineering methods used to design a centrifugal pump are the same as those to design a centrifugal compressor. Yet, there is one important difference: the need to deal with cavitation in pumps. Radial turbine Centrifugal compressors also look very similar to their turbomachinery counterpart the radial turbine as shown in the figure. While a compressor transfers energy into a flow to raise its pressure, a turbine operates in reverse, by extracting energy from a flow, thus reducing its pressure. In other words, power is input to compressors and output from turbines. Turbomachinery using centrifugal compressors Standards As turbomachinery became more common, standards have been created to guide manufacturers to assure end-users that their products meet minimum safety and performance requirements. Associations formed to codify these standards rely on manufacturers, end-users, and related technical specialists. A partial list of these associations and their standards are listed below: American Society of Mechanical Engineers:BPVC,PTC. American Petroleum Institute: API STD 617 8TH ED (E1), API STD 672 5TH ED (2019). American Society of Heating, Refrigeration, and Airconditioning Engineers: Handbook Fundamentals. Society of Automotive Engineers Compressed Air and Gas Institute International Organization for StandardizationISO 10439, ISO 10442, ISO 18740, ISO 6368, ISO 5389 Applications Below, is a partial list of centrifugal compressor applications each with a brief description of some of the general characteristics possessed by those compressors. To start this list two of the most well-known centrifugal compressor applications are listed;