Abstract: A pressure control system for a CA room including a bladder and an active displacement control that are operable to control the internal pressure of the CA room through variations in displacement. The system may include a controller configured to vary the displacement of the bladder based on the difference between barometric pressure and CA room internal pressure. The system may control bladder displacement based on the output of a differential pressure sensor that measures the pressure differential between the CA room and barometric pressure, or the output of separate internal and external sensors that separately measure CA room pressure and barometric pressure. The bladder may be an inflatable bladder and the active displacement control may inflate and deflate the bladder to vary its displacement within the CA room. The active displacement control may include an active air supply with a blower that can quickly inflate and deflate the bladder.