Damper selection and application considerations

In selecting dampers, the application considerations outlined on this page should be carefully examined to ensure job requirements are met. If special features such as blade reinforcements, heavy duty linkages, bearings, axles and frames, special seals and finishes and construction of corrosion materials are required, they can be incorporated at additional cost. If you doubt, please consult our factory for advice.

Air Leakage
Both internal and external leakages should be considered. Some applications may have very stringent air leakage requirements such as ventilation systems of civil defense shelters. It may be difficult for normal damper to achieve very low air leakage and special seals or construction may be necessary. Low leakage damper requires much higher torque to close the damper against the special seals. Hence, it is important to determine the maximum acceptable air leakage.

Static Pressure
Dampers are subject to maximum pressure differential when they are fully closed. As they open, airflow increases and static pressure is converted to velocity pressure and the forces on the damper become more dynamic than static. At higher operating pressure, the torque required to open and close the damper increases. It is important to determine the maximum possible static pressure in normal operation when selecting damper.

Velocity
As air velocity increases, dampers encounter higher forces, resulting in an increase in the deflection of the blades. At high air velocity, the blades are also subject to twisting as they move. As a result, it may be necessary to reinforce the blades. At higher air velocity, the torque required to open and close the damper increases. Hence, it is important to determine the maximum air velocity in normal operation when selecting the damper.

Turbulence
Excessive turbulence and pulsation of airflow may damage the seals, cause bending and twisting of damper blades, and stress on bearing and linkages, resulting in accelerated wears on these parts. This can happen when dampers are located near large fans, abrupt duct transition or near elbow without turning vane. Dampers located near to fan discharge must be reinforced, due to severe turbulence that can easily cause fatigue failure in the dampers. In addition, more or larger actuators may be needed, due to the additional torque which may have resulted from the turbulence. After installation, it is recommended that the dampers be inspected during actual operation over the full range of positions (from fully opened to fully closed positions) to ensure that the damper blades are not subject to severe vibrations. Such vibrations can be due to damper blades being in resonance in frequency generated by the fan blades. If severe vibrations occur, stiffening of the blades, additional linkages and actuators may be essential to prevent failure of the dampers. If possible, dampers should be located as far away from the fan discharge as possible. As a guide, dampers should be located …

Temperature
Typical operating temperature in HVAC systems is limited to 70°C. Some applications may require higher temperature which may necessitate the use of high parts such as seals and bearings, heat resistant material of construction and special actuator.

Corrosion
Damper in conventional HVAC systems typically use hot-dipped galvanized steel material that provides sufficient protection against corrosion. More protection may be required for some applications such as:
• dampers in exhaust duct carrying corrosives fumes;
• dampers used for outdoor air intake in building in the coastal area, marine and industrial environment;
• dampers near cooling coil, etc.

Alternative material of construction such as aluminum or stainless steel should be used.

Nuclear/Seismic
Dampers used in nuclear power plants and other similar facilities may be required to operate during and after and earthquake. Such dampers are required to meet stringent applicable regulations and testing to ensure that they can meet specified levels of vibration. Dampers for such application must be designed to withstand low frequency, high amplitude multi-axis vibration.