A variety of high frequency chest compression (“HFCC”) systems have been developed to aid in the clearance of mucus from the lung. Such systems typically involve the use of an air delivery device, in combination with a patient-worn vest. Such vests were developed for patients with cystic fibrosis, and are designed to provide airway clearance therapy. The inflatable vest is linked to an air pulse generator that provides air pulses to the vest during inspiration and/or expiration. The air pulses produce transient cephalad air flow bias spikes in the airways, which move mucous toward the larger airways where it can be cleared by coughing. The prior vest systems differ from each other, in at least one respect, by the valves they employ (if any), and in turn, by such features as their overall weight and the wave form of the air produced.