A valve is provided for use on a control moment gyroscope (CMG) having a housing separating an internal environment from an external environment. The valve includes a valve housing, a valve element, and bellows. The valve housing is configured to couple to the CMG housing and includes an inner surface defining a cavity, an outer surface, and an opening extending therebetween. The valve element is disposed within the valve housing cavity and is movable between a closed position, in which fluid is prevented from flowing through the valve housing opening, and an open position, in which fluid may flow through the valve housing opening. The bellows is disposed within the valve housing and coupled to the valve element and has an internal chamber. The bellows selectively moves the valve element closed and open in response to a differential pressure between the bellows internal chamber and the valve housing cavity.