The present invention relates generally to the construction of multi-blade air, smoke or fire dampers, and in particular, to mechanisms for rotating the damper blades to a desired orientation.
Generally, multi-blade dampers comprise a plurality of stamed blades pivoted for rotation within a damper frame. A common blade linkage is provided which causes simultaneous rotation of the damper blades between an open and a closed position in response to a particular condition. For example, maintaining the damper blades at a selected position intermediate the fully opened and closed positions provides an air control function. Maintaining the damper blades in either their fully closed or fully open position provides a fire or smoke control function. Examples of multi-blade dampers having such capabilities may be found in my U.S. Pat Nos. 4,113,230 and 4,113,232, both dated Sept. 12, 1978, the subject matter of each of which is incorporated by reference as if fully set forth herein.
A variety of mechanisms have been developed for operating the blade linkages which are used to cause articulation of the damper blades with respect to the damper frame. One such mechanism involves the use of a retractable cable in conjunction with an appropriate biasing means. The cable is generally attached to the blade brackets or blade linkages within the damper, and is then normally threaded through a ferrule disposed in the damper/duct wall for attachment to an actuator motor positioned outside of the duct in which the damper is located. A variety of means can be used to bias the blades toward a selected orientation, such as one or more springs extending between the damper frame and the blades. In this manner, a variety of functions may be developed. For example, selective retraction of the cable by the actuator motor will cause the damper blades to rotate to a desired orientation, against the force applied by the biasing device, providing an air control function. Providing a releasable means between the cable and the damper blades, such as a fusible link or the like, permits releasable engagement between the actuator motor and the damper blades which, depending upon the orientation of the biasing means, provides a fire or smoke control function. In fact, combinations of these functions may be developed, if desired.
Alternatively, it is known to operate such dampers using a shaft drive. Generally, rotation of the shaft drive through an arc of approximately 90.degree. is caused to substantially correspond to the rotation of the damper blades approximately 90.degree., between their fully opened and closed positions. Various motorized actuators are known for use in rotating such operator shafts through their desired arc. One advantage provided by shaft-type operators is that they are advantageously controlled from a remote source, to adjust the flow of air through the damper by rotating the damper blades a preselected degree intermediate the fully opened or closed position. The use of shaft-type operators is also generally indicated when relatively large dampers must be operated, since shaft-type operators are generally required to deliver the amounts of power and torque necessary to properly operate such dampers, as opposed to the cable-type operators which generally can not.
While the use of shaft operated dampers may be preferred in certain instances, such operators often tend to exhibit a variety of disadvantages. For example, such operators are typically relatively difficult and expensive to install, primarily due to the fact that they are normally installed only after the damper has been installed within the duct. Such a requirement makes accurate installation difficult and expensive, and often results in improperly aligned damper/operator combinations. This is particularly so since such damper operators are often specifically designed for use with a particular damper type, promoting the potential for mismatching between these components during installation. For this reason, careful alignment procedures must be followed, generally requiring the use of highly skilled labor to obtain a proper installation.
As a further consideration, irrespective of the means used to rotate the damper blades, it is generally expected that there is a direct correspondence between the rotation of the damper blades and the percentage of air flow permitted to pass through the damper. For example, a 10.degree. movement of the operator shaft, which substantially corresponds to 10.degree. opening of the damper blades, is generally assumed to establish a corresponding air flow through the damper of approximately 10%. In actuality, particularly in conjunction with parallel blade-type dampers, it bas been found that the relationship between damper blade opening and the air flow through the damper is not linear. Rather, during the initial stages of damper blade opening, a correspondingly greater percentage volume of air has been found to pass through the damper for a given degree of blade rotation than during the final stages of damper blade opening. As the damper blades approach the fully opened position, a correspondingly smaller increase in air flow is achieved for a given degree of blade rotation.
Since parallel blade-type dampers generally cannot provide a linear relationship between the percentage flow of air through the damper and the degree of damper blade rotation, the use of opposed, rotating blade dampers is generally recommended when such linear air flow relationships are necessary. However, oposed blade dampers tend to produce other disadvantages which seriously limit their utility, particularly increased resistance to air flow.
It, therefore, remains desirable to develop a damper operator which overcomes the foregoing disadvantages without sacrificing proper operation of the damper structure used. It is particularly desirable to develop a damper operator which can be used to provide parallel blade-type dampers with linear air handling characteristics, and which permits cable-type actuator motors, as well as shaft-type actuator assemblies, to be used in conjunction with dampers of various sizes.