Patient interface and a speech valve therefor

A patient interface configured to be connected to a respiratory therapy system to deliver a flow of breathable gases to a user, the patient interface comprising:

• a mask body;
• a mask seal secured to the mask body and configured to form a seal with the user's face, at least around the user's mouth, the mask body and mask seal being arranged to define an interior breathing chamber of the patient interface;
• an inlet port to the breathing chamber configured to receive the flow of breathable gases into the breathing chamber;
• and
• a user actuated speech valve operable to selectively open a speech flow path from the breathing chamber to atmosphere when the user wishes to speak, the speech valve comprising:
• at least one vent opening;
• a valve flap pivotally mounted in the breathing chamber so as to selectively occlude the vent opening in a first position and open the vent opening in a second position;
• and
• a spring configured to produce a biasing force that tends to move the valve flap towards the first position;
• wherein the valve flap is exposed to pressure within the breathing chamber, which exerts a pneumatic bias tending to move the valve flap towards the first position.