Dampers

One way of getting even air distribution is through the use of duct dampers. Dampers balance airflow or can shut off or open certain ducts for zone control. Some are located in the grille, and some are in the duct itself. There are three types of dampers used in air-conditioning ductwork - butterfly, multiple blade, and split damper (fig. 7-44). When installing a damper, always draw a line on temperature control.

Fire Dampers

Automatic fire dampers should be installed in all vertical ducts. Ducts, especially vertical ducts, will carry fumes and flames from fires. Fire dampers must be inspected and tested at least once a year to be sure they are in proper working order. There are two types of fire dampers, which are fail-safe units - spring-loaded to close and weight-loaded to close. Fire dampers are usually held open by a fusible link. Heat will melt the link and the damper will close by either gravity, weights, or springs (fig. 7-45).

Fans

Air movement is usually produced by some type of forced airflow. Fans are normally located in the inlet of the air conditioner. Air is moved by creating either a positive pressure or negative pressure in the ductwork. The two most popular types of fans are the axial flow (propeller) or radial flow (squirrel cage) (fig. 7-46).

Figure 7-45. - Fire damper in OPEN position.

Figure 7-44. - Three types of duct dampers.

Figure 7-46. - Principal types of fans: A. Radial flow; B. Axial flow.