Adjustable inlet diffuser vanes on centrifugal air compressors are implemented to:

Adjustable inlet diffuser vanes on centrifugal air compressors are primarily used to change the operating characteristics of the compressor. These vanes play a critical role in optimizing performance across various operating conditions. By adjusting the angle of the vanes, operators can control the airflow entering the compressor, which directly affects both the pressure and volume of air being compressed.

This adjustability allows for improved efficiency, better matching of the compressor performance with system demands, and enhanced stability across a wider range of operating conditions. It can also lead to reduction in surge and increase the operational flexibility of the compressor, allowing it to operate effectively under variable load conditions.

In contrast, changing airflow direction to remove moisture or foreign particles does not relate to the function of inlet diffuser vanes. While moisture and foreign particles could impact compressor performance, the adjustment of diffuser vanes is not a mechanism used for their removal. Similarly, preventing back or reverse flow of air is typically achieved through other design features such as check valves or specific configurations of the compressor rather than through the operation of adjustable inlet diffuser vanes.