US PATENT SUBCLASS 454 / 360
.~.~.~ Including counter balancing means

Current as of: June, 1999
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454 /   HD   VENTILATION

339  DF  HAVING OUTLET AIRWAY {7}
358  DF  .~ Having readliy movable air regulating louver, damper, or cover {3}
359  DF  .~.~ Including backdraft preventer {1}
360.~.~.~ Including counter balancing means

DEFINITION

Classification: 454/360

Including counter balancing means:

(under subclass 359) Subject matter including a means which mechanically biases the backdraft preventer toward a particular position.

(1) Note. The backdraft preventer is usually biased to an

open or closed position.

SEE OR SEARCH THIS CLASS, SUBCLASS:

359, for a backdraft preventer biased to a particular position by a naturally occurring force such as gravity.