Flow Valve

A lung demand regulator comprising:

• a flow valve comprising a valve member configured to be displaced between a closed position in which the valve member seals against a valve seat of the flow valve, and an open position in which a breathing gas flow path is provided between the valve member and the valve seat;
• wherein the valve member and/or the valve seat is shaped such that a cross-sectional area of the breathing gas flow path increases at a first rate during displacement of the valve member relative to the valve seat through a first displacement range, and the cross-sectional area of the breathing gas flow path increases at a second rate during displacement of the valve member relative to the valve seat through a second displacement range, the first rate being different to the second rate;
• the valve member comprises an outer surface, the outer surface comprising a first tapered portion and a second tapered portion, the first tapered portion and the second tapered portion being arranged coaxially;
• a diaphragm exposed to an ambient pressure on a first side and an internal chamber of the lung demand regulator on a second side, the diaphragm being configured to flex according to a pressure differential between the first side and the second side;
• and
• a flow regulation mechanism coupled to the diaphragm and configured actuate the flow valve by displacing the valve member relative to the valve seat in response to flexing of the diaphragm when a pressure in the internal chamber falls below an ambient pressure;
• wherein greater flexing of the diaphragm causes greater displacement of the valve member;
• and
• wherein the valve member is biased to return to the closed position when the pressure differential falls below a threshold.