What happens when the inlet vanes of a centrifugal compressor are held in a closed position?

When the inlet vanes of a centrifugal compressor are held in a closed position, it reduces the amount of airflow entering the compressor. This limitation on airflow results in the compressor experiencing higher pressure ratios at the start-up phase, which can lead to a decrease in the starting torque required to initiate rotation. A higher pressure ratio means that more force is required to start moving the compressor. As a result, the starting torque becomes reduced because the compressor is working against a more considerable resistance when the vanes are closed.

In centrifugal compressors, the angle of the inlet vanes is crucial for regulating the flow. When the vanes are fully shut, the ability to efficiently draw in air is compromised, affecting overall performance and stability during startup but primarily influencing the torque required to overcome initial operational resistance.

This is a fundamental principle in compressor operation, emphasizing the importance of airflow in determining how effectively the compressor can start and operate under various conditions.