Movable blade damper

A flue gas damper comprising:

• first and second axially aligned, spaced apart tubular duct members;
• a pressure chamber surrounding the adjacent ends of the first and second duct members;
• a blade member located between the first and second duct members within the pressure chamber, said blade member being substantially planar and having an aperture defining a first section and an imperforate second section;
• first and second lifting members secured to opposed edges of the blade member, each lifting member having a first end secured to the blade member and a second end extending out of the pressure chamber in the plane of the blade member;
• means, situated outside the pressure chamber, for positioning the first and second lifting members and thereby the blade member between a first position, in which the blade aperture is aligned with the first and second duct members, and a second position, in which the imperforate second section is aligned with the first and second duct members;
• first and second substantially rigid sealing strips mounted adjacent the blade member and the first and second duct members, respectively, at a substantially fixed separation adequate to prevent binding between the blade member and the sealing strips, said sealing strips having a hardness and a rigidity adequate to substantially prevent buildup of hardened fly ash between the blade member and the sealing strips, said blade member cooperating with the sealing strips to maintain the sealing strips adjacent the blade member when the blade member is positioned in both the first and second positions;
• and
• means, mounted exterior to the pressure chamber, for pressurizing the chamber with air to promote passage of air out of the chamber between the sealing strips and the blade member into the duct members, thereby substantially preventing the leakage of flue gas from the first to the second duct member when the blade member is in the second position.