Butterfly Dampers

Our line of Butterfly dampers are available for a wide variety of applications in round ducting where low leakage, flow control, or a combination of the two are required. Flow characteristics are similar to that of a single blade Louver Damper design and can be supplied in varying degrees of shutoff (90 to 99.9%) depending on the specific applications and seal arrangement. Design components include rolled plate steel frame with plate steel or rolled angle flanges, plate steel blade (stiffened A/R), and round bar shafts (stub and full length).

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Flextech Industries offers three basic seal designs:

  • Swing-through: Swing-through seals are used in extremely dirty applications where tight shut-off is not required. The gap around the blade can be increased or decreased to suit the customer’s individual need.
  • Step Seat: The step seat is standard for butterfly dampers and is recommended for relatively clean flue gas applications with up to a 99% sealing efficiency. This design utilizes a rolled bar which is welded to housing the blade-closed position.
  • Tadpole: A tadpole seal is also recommended for relatively clean applications. The tadpole seal is constructed of a woven high-temperature silica cover with a silica rope bulb. This design provides up to 99.9% sealing efficiency.


All packing gland designs are compression-type with either a single wrap, for low to mid-temperature and clean to moderate particulate buildup, to a 3-wrap design for all other applications. The packing gland is located between the external frame and the bearing brackets for ease of maintenance.

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Butterfly Dampers5When modulation is necessary, Flextech can supply an opposed design to better control the airflow through the damper. Our typical linkage is non-adjustable but fully adjustable can be made available upon request.


Flextech can include most types of actuation requirements, i.e. electric, pneumatic, manual, etc…, as well as accommodate other requirements such as an extended shaft or mounting of a customer supplied device.