US Patent 8936203 Barometric relief air zone damper

A control system for an HVAC system serving at least two zones, each zone receiving conditioned air by way of a zone duct, each zone duct including a zone damper having a first portion and second portion controlled by a actuator to move between an open and a closed position in response to a zone thermostat, a second portion responsive to the static pressure in a HVAC system to open and bleed an amount of conditioned air past the damper when the static pressure of the system increases above a selected level, and a weight adjustment for modifying the torque exerted by the second portion against the system static pressure to adjust the selected level.