Rectangular damper blades generally open and close by rotating about their longitudinal center line. Such blades are usually positioned within an appropriate rectangular inlet opening, and blade seals are often situated between the inlet opening and the blade's longitudinal edges.
In designing the specific geometry and mounting configuration of the blade seals, several interrelated factors need to be taken into account. These factors include sealing ability, closing force, friction, blade twist, drive requirement, and tolerance of misalignment and overshoot. Sealing ability is generally a function of the closing force of the blade and/or the radial interference at the seal between the blade and the inlet opening. Increasing the closing force, however, often requires the use of relatively large drives and sturdy blades that resist twisting. Likewise, increasing radial interference increases friction which also requires larger drives and sturdier blades. Overshoot is the distance the blade attempts to travel after reaching its intended closed position. Some seal designs have an abrupt closing point that provide little or no tolerance to blade twist or overshoot, making them susceptible to both leakage and damage. And light weight blades driven by small drive motors are usually sensitive to overshoot or allow only the use of light weight seals that provide inadequate sealing.
Previous blade designs typically address some of the above problems while compromising on others. Consequently, a need exists for a single, well designed damper blade that addresses all of the above problems.
Therefore, an object of the invention is to provide a pair of damper blade seals whose sealing force increases in response to the pressure differential across the damper blade.
Another object is to provide a seal whose sealing force is generally aligned with the damper blade to minimize the bending moment on the blade.
Another object is to provide a seal that offers a sliding contact as the blade closes, thereby allowing for blade twist and overshoot.
Yet another object is to provide a pair of generally interchangeable seals, one of which is attached directly to an edge of the blade and the other being attached to a similar edge next to the blade.
A further object is to provide a pair of seals that augment the closing force of the blade in the presence of a pressure differential across the blade.
A still further object is to provide a direct drive damper blade having sliding contact blade seals for eliminating the need for accurate blade alignment and linkage adjustment.
These and other objects of the invention will be apparent from the description of the preferred embodiment which follows hereinbelow and the attached drawings.