What is a damper?

A damper is a device consisting of one or more rotating blades contained in an open frame. Their primary purpose is to regulate flow at key points in a system. They can also be designed to modulate flow. There are several different types of dampers in HVAC, and each type serves a purpose in the overall system.

Control dampers are the most common dampers used in duct systems. The type of damper you use will depend on the needs of the application.

Control dampers, open and closed — This is a control damper with single thickness blades.

How do they work?

In HVAC, dampers control the flow of air. They work much like a valve that controls water flow. The damper’s blades will rotate along axles to either open or close the damper. In most dampers, these blades will be tied together with a linkage assembly so that all blades rotate at the same time. When open, air can flow through the free area between the damper’s blades. When closed, the blades will block incoming air.

Most dampers will use an actuator to control blade rotation. Actuators are attached to the driving blade axle of the damper. The damper's linkage will translate this rotation to the other blades, so that all blades rotate together. The linkage can be configured in one of two ways:

The linkage rotates all blades to the same angle. This is parallel blade action.
The linkage rotates each blade to an opposite angles to its neighbors, which is called opposed blade action.

Actuators can be powered by an electric motor, by a pneumatic piston, or by hand. Control dampers will often use electric actuators because of their automation capabilities. When tied to a central control system, electric actuators can be set to automatically open and close dampers.

The type of damper and its location in your system will help you determine if an actuator is required and what type to use. For example, pneumatic actuators will require a central air compressor to operate. For certain damper types, the damper may remain partially closed to modulate the amount of air flowing through the damper.

Damper Types

The following are various types of dampers and what they do in your HVAC system.

Control Dampers: Dampers that open and close to direct airflow through ductwork. These dampers will either be fully open to allow air through or fully closed to block airflow. Control dampers are installed throughout the system to keep air moving to the right spot in your building.

Balancing Dampers: Dampers that remain open at predetermined blade angles to balance air pressure between duct sections. Technicians will manually adjust the angle of the blades until pressure is balanced, then lock the blades in place. Balancing dampers eliminate the heating and cooling issues caused by pressure imbalances, such as drafts and cold spots.

Modulating Control Dampers: Control dampers that will hold blade positions between fully open and fully closed. Modulation allows control of the amount of air flowing through the duct when the damper is open. Modulating dampers require a modulating actuator to hold multiple blade positions.

Backdraft Dampers: Dampers with blades that have off-center axles, which rotate when pushed from one side. Backdraft dampers open when air flows through a duct in the intended direction but will not open when air flows in the opposite direction. The blades will close on their own when the air flow stops. These dampers are useful for applications where air will move in one direction.

Pressure Relief Dampers: Backdraft dampers designed to open as air pressure reaches a predetermined threshold. Pressure relief dampers are designed to relieve pressure, allowing the excess pressure to escape the system without damaging HVAC components.

Industrial Dampers: Dampers built from strong materials for heavy duty applications. As the name implies, industrial dampers are designed for industrial locations such as factories and power plants. These locations will typically require massive airflow at extreme pressures. Industrial dampers can serve a variety of roles based on their design.

Tunnel Dampers: Industrial dampers built for the major demands of airflow in tunnel structures. Generally, tunnel dampers are opened when trains passes into the station. This helps mitigate the piston effect, which can cause sudden bursts of air. These dampers are commonly used in transit tunnels to help provide a comfortable environment for tunnel occupants. They can also be used in an emergency to help control the spread of smoke and fire.

Fire Dampers: Dampers used at the penetrations in a fire barrier to complete barrier’s fire resistance. Fire dampers are designed to close at the first signs of a fire, to prevent flames from spreading through the HVAC penetrations in the fire barrier. These dampers will have a heat response device that triggers closure when temperatures exceed a given threshold. Read more about fire dampers with our blog article "Fire Damper Types".

Smoke Dampers: Dampers used throughout the HVAC system to prevent the spread of smoke through ductwork. Smoke dampers are connected to a smoke detector which monitors the air stream for noxious fumes. The damper will close at the first signs of smoke and prevent it from spreading through the duct.

Round Dampers: Dampers with round frames or with round transition collars. These dampers are designed for spiral or round-shaped ductwork. Control, balancing, and backdraft dampers can be round to fit the right duct.

Three dampers with various blades — The two dampers are on the left have single thickness blades. The damper on the right has airfoil blades.

Which Damper is Best?

The answer to this question will vary depending on the application. In this case, the “application” is a combination of the damper’s intended installation location and the airflow requirements at that location. You will use various damper types throughout the HVAC system to keep air moving. Start by focusing on a particular application in the system.

Gather the necessary data for that application, like the size of the install location and the required amount of airflow. With this data, you can choose the right damper for the task at hand.

AWV and Dampers

AWV can help you choose the right dampers for your next project. We build dampers for commercial and industrial projects. Each damper is built from the ground up, so that it meets the requirements of your application.

Meet your airflow requirements with dampers built for your project. Contact AWV and let’s get started!

Dampers 101: What is a Damper?