A centrifugal compressor is characterized by its radial discharge flow. Air is drawn into the center of a rotating impeller with radial blades. It is pushed out towards the perimeter of the impeller by centrifugal forces. The radial movement of the air results simultaneously in a pressure rise and a generation of kinetic energy. Before air is led to the center of the impeller of the next compressor stage, it passes through a diffuser and a volute. This is where kinetic energy is converted into pressure.
Each stage takes up a part of the overall pressure rise of the compressor unit. In industrial machinery, the maximum pressure ratio of a centrifugal compressor stage is often not more than 3. Higher pressure ratios reduce stage efficiency. Multi-stage applications allow the possibility of inter-cooling to reduce the power requirement. Multiple stages can be arranged in series on a single, low-speed shaft. This concept is often used in the oil and gas or process industry.
Since the pressure ratio per stage is low, a large number of stages and/or multiple compressor sets are used to achieve the desired pressure. For air compression applications, a high speed gearbox is integrated with the compressor stages to rotate the impellers on high speed pinions. The impeller can have either an open or closed design.
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