A method or device is provided for connecting a centrifugal blower to a process requiring the flow of forced air such that the flow of air may be reversed. The method is applied to a process that benefits from the switching of the direction of air flow to either positive pressure or suction. The method was developed primarily use in the forced aeration composting process but may have other applications. The invention consists of a damper with a plurality of vanes rotating on parallel shafts, which is closely coupled to both the inlet and outlet of a centrifugal blower. When set to provide positive pressure, the vanes direct outside air to the blower intake and direct the blower discharge to the process requiring aeration. When set to provide suction, the vanes direct air from the process to the blower intake and direct the blower discharge to a port that may be connected to an air pollution control device. The shafts are connected by co-planar crank arms and linkages, such that the damper setting may be switched by a single actuator, thereby simplifying the automation of the reversal of air flow.