Lung demand valve

A lung demand valve, comprising:

• a body within which is disposed a diaphragm and a valve assembly having a valve inlet, the valve assembly and diaphragm arranged to cooperate to control the delivery of breathable gas to a user, one side of the diaphragm being exposed to ambient pressure;
• a breathable gas inlet fluidically connected to the valve inlet inside the body and arranged to be fluidically connected to a supply of breathable gas;
• a whistle coupled to the body and extending from the inside to the outside of the body, the whistle having a whistle inlet disposed within the body and fluidically connected to the breathable gas inlet inside the body, and a whistle outlet disposed outside the body;
• and
• a manifold disposed within the body and having at least three ports, wherein each port is fluidically connected to one of the valve inlet, breathable gas inlet and whistle inlet,
• wherein in use, when the pressure of the breathable gas in the breathable gas inlet is less than a threshold, breathable gas flows from the breathable gas inlet through the whistle inlet and outlet, thereby causing the whistle to sound outside of the body.