Abstract: A diver's demand valve has a diaphragm 15 with a centrally located rigid element 16 which pivots with a lever effect on an eccentric port 22 upon establishing an operative pressure difference across the diaphragm to open and close the valve. An abutment surface 30 prevents unwanted pivoting and a spring 27 keeps the rigid element 16 seated except during operative pressure differences.For a diver's exhalation demand valve an "anti-squeeze", safety, flap valve 34 may be provided in the rigid element 16.

Abstract: The present invention is directed to a closed circuit underwater breathing apparatus having a mouthpiece and an outward and return connection leading from the mouthpiece to an inflatable breathing bag and back respectively to form a breathing circuit. A carbon dioxide absorbent is arranged in the breathing circuit. In use, exhaled gases flow from the mouthpiece through the outward connection to expand the breathing bag and then, on inhalation, they return from the breathing bag through the return connection to the mouthpiece. The apparatus also includes a demand valve controlling a connection between the mouthpiece and an inlet for an attachment to a supply of breathable gas.