Dampers & Airflow Control
Volume dampers, fire dampers, smoke dampers, splitter dampers, backdraft dampers, and opposed blade dampers.
- Identify volume, splitter, and backdraft damper types and applications
- Explain fire damper and smoke damper operation and code requirements
- Describe duct boots, offsets, and takeoff fitting construction
Lesson 1
Volume & Splitter Dampers
Volume Dampers
A volume damper controls the amount of airflow through a duct section. It consists of a blade (or multiple blades) that rotates on an axle inside the duct. An external handle or actuator controls the blade position from fully open to fully closed.
Single-Blade Damper
Construction: One blade on center pivot
Application: Branch ducts, small sections
Control: Manual handle or actuator
Characteristic: Non-linear flow control
Opposed-Blade Damper
Construction: Multiple blades rotating opposite
Application: Main ducts, mixing boxes
Control: Actuator (typically motorized)
Characteristic: Near-linear flow control
Parallel-Blade Damper
Construction: Multiple blades rotating same direction
Application: Face and bypass, two-position
Control: Actuator
Characteristic: Non-linear, good for on/off
Opposed vs Parallel Blade
The exam specifically tests the difference between opposed-blade and parallel-blade dampers. Opposed-blade dampers provide the most linear airflow control because adjacent blades rotate in opposite directions, creating uniform resistance across the duct. Parallel-blade dampers deflect air to one side and are better for two-position (open/closed) applications.
Splitter Damper
A splitter damper divides airflow at a branch takeoff. It is a single blade positioned at the junction of the main duct and branch. The blade angle determines how much air enters the branch versus continuing in the main duct. Splitter dampers provide rough balancing at branches but are less precise than volume dampers.
Damper Markings
Damper handles should be positioned so the handle is parallel to the duct when open and perpendicular when closed. This allows a technician to see damper position at a glance during balancing.
Opposed-blade dampers provide the most linear airflow control and are preferred for modulating applications. Parallel-blade dampers are best for on/off control. Splitter dampers divide airflow at branch takeoffs for rough balancing.