Valve means

826,280. Respiratory apparatus. BRITISH OXYGEN CO. Ltd. March 17, 1958 [April 24, 1957], No. 13075/57. Class 81 (2). A valve assembly for breathing apparatus comprises gas inlet and outlet chambers 14, 15 communicating through a valve port 18, a pressure-responsive member 20 exposed to pressure in the inlet chamber 14 and to atmosphere and carrying a valve 40 movable either manually or according to the patient's demand to open the port 18 and close a vent or by pressure in the inlet chamber 14 to close the port 18 and open the vent. The inlet and outlet chambers 14, 15 are separated by a partition 13 with the valve port 18 and have inlet and outlet ports 16, 17 respectively. The valve 40 is carried by a valve stem 24 which is connected to and passes through a diaphragm 20. A knob 27 by which the valve port 18 may be opened manually is secured on the free end of the valve stem 24. The vent is formed by a tube 33 extending into the outlet chamber 15 coaxial with the valve stem 24 and passing through the outlet chamber wall to communicate with atmosphere through a non-return valve 36 and holes 39. When gas is supplied to the inlet chamber 14 continuously at positive pressure, the valve port 18 may be opened by depressing the knob 27 manually and thus moving the valve 40 to seat on the top of the tube 33. This closes the vent and permits gas to flow to the patient to induce inspiration. On releasing pressure on the knob 27, the gas moves the diaphragm 20 outwardly of the inlet chamber 14 and thus moves the valve 40 to close the valve port 18 and open the vent, so that the patient can exhale naturally by way of the outlet chamber 15, tube 33 and non-return valve 36. If the patient begins to inhale naturally while the valve port is closed, the reduction in pressure created in the outlet chamber 15 permits the valve 40 to slide on the stem 24 against a spring 42 thus opening the valve port 18. When the inlet 16 is connected to a gas supply the pressure of which varies according to the patient's demand, inhalation reduces the pressure in the outlet and inlet chambers 15, 14, the valve port being initially slightly open. The diaphragm 20 moves inwardly of the inlet chamber 14 and holds valve 40 open. Expiration under demand conditions increases the pressure in the inlet and outlet chambers so that the diaphragm 20 moves to close the valve port 18 and open the vent. In a modification, a passage (not shown) in the valve stem connects the inlet to the vent during exha