A damper or louvres is a multi-flow control device used to throttle the large flow of the air at lower pressure.
They are commonly used in HVAC, boiler application and in the furnaces to control the flow of the air.
Following is the image of the damper used to throttle flow by using a plate.
There are two types of design are used for the damper.
Parallel vane damper used to throttle the airflow using multiple rectangular vanes synchronously.
Radial damper use arrangement of vane like petal of the flower to throttle flow through a circular opening.
Following is the image of the radial damper contain set of vanes, the outside tube is used to synchronize the motion of the vanes to stop the flow.
An automated or motorised damper is also used which is controlled by the solenoid valve.