6″ Vertical / Horizontal Barometric Bypass Damper (SPECIAL ORDER – NON – RETURNABLE). BH and BV Series barometric bypass dampers are used to automatically bypass excess air when increases in duct pressure occur due to closing of zone dampers. Various relief air control settings are accomplished by simple adjustment of the weight on the arm. Barometric bypass dampers are recommended for systems up to 0.75” WC of static pressure. These come as horizontal (BH) or vertical (BV) configuration in both round and rectangular.