Double acting respirator pump apparatus including a pump member reciprocable with respect to two pump chambers to deliver air to a patient via a respirator exhalation system, which also facilitates exhalation of the patient. The exhalation system has a pump unit that is operatively connected to an exhalation valve member and configured for selectively generating an air pressure sufficient for pressurizing one side of the valve member for closing the same when said exhalation system is operating in inhalation mode, and may be operated for opening to allow the patient to exhale therethrough.
