Balancing dampers are used in supply ducts and return ducts to adjust the airflow to the design values. In air-moving systems, dampers are used to:
- balance airflow,
- control airflow,
- resist the passage of fire, or
- resist the passage of smoke
These dampers can be of simple construction or of multi-blade construction. Multi-blade dampers operated by electric motors or pneumatic pistons to vary the flow rate are called control dampers. Dampers used to resist the passage of fire are called fire dampers, and these can be multi-blade dampers.
Dampers used to resist the passage of smoke are called smoke dampers and these can also be either multi-blade or curtain. Combination dampers can be used to balance airflow, control airflow, resist the passage of fire, and resist the passage of smoke.
The multi-blade fire dampers are kept open by a fusible link and are spring-loaded. In a fire situation, the hot gases cause the bond to separate, allowing a spring to close the blades. Instead of fusible links, some manufacturers use other heat-sensitive devices.
The smoke dampers have standards includes construction requirements and tests for cycling, temperature degradation, dust loading exposure, salt-spray exposure. air leakage, and operation under airflow. These dampers are classified as I, II, or III. Maximum leakage rates of dampers are listed below:
Thc particular class of damper specified should be selected based on the requirements of the application. Class 1 dampers are chosen for applications that require a very right damper, such as a return air damper.
Class II or Ill smoke dampers are chosen at which dampers in the supply and return ducts can have some leakage without adversely affecting smoke control system performance.