Exhalation valve for respirator

An exhalation assembly which includes:

• a hollow flow-through body, having an air inlet port and an air outlet port, wherein said inlet port is arranged to receive air for supplying to a patient, and said air outlet port is arranged to provide air to a patient;
• and
• an exhalation valve connected to said flow-through body, for facilitating selectable exhalation by a patient to whom air is being supplied, wherein said exhalation valve includes:
• an air exhalation port arranged to permit therethrough an outflow of exhaled air;
• a valve member arranged to selectably cover said exhalation port in response to a closure pressure applied thereto, and to uncover said exhalation port in response to an exhalation pressure applied thereto from said flow-through body through said exhalation port;
• and
• a pressure source for selectably applying a closure pressure to said valve member;
• wherein said valve member is operative to cover said exhalation port in response to at least a minimum closure pressure which has a greater magnitude than an opposing a exhalation pressure;
• and
• means for changing the effective working area of the valve member from a first working area to a second working area which differs from said first working area.