A pressure reducing valve for use in a system adapted to deliver a breathing gas to a patient. The pressure reducing valve is structured to communicate a flow of breathing gas to such a patient's airway during an inspiratory phase. The pressure reducing valve is structured to isolate the flow of breathing gas from the patient's airway and to dump the flow of breathing gas and a flow of exhalation gas to atmosphere during the expiratory phase. The flow of breathing gas is dumped to atmosphere through a first number of ports； whereas a flow of exhalation gas is dumped to atmosphere through a second number of ports. Because the flow of breathing gas remains isolated from the flow of exhalation gas, less effort is required by a patient during the expiratory phase.
