Inlet guide vanes valve. It is a valve assembly at the air inlet of a blower or compressor (generally, centrifugal) to provide ‘pre-swirl’ of airflow in the same rotational direction of impeller.
IGV has multiple triangular blades that allow the air to flow into the compressor in a swirl direction. This “pre-swirl” air reduces the amount of power required from the main motor to spin the air entering the impeller. The directional flow increases as the vanes close, putting less load on the impeller compared to a butterfly valve. This makes inlet guide vanes more efficient during turndown than inlet butterfly valves.
(See also, ‘Compressor capacity control’)