Abstract: In a breathing apparatus of the closed circuit type wherein breathable air is recirculated with the removal of carbon dioxide and the replenishment of oxygen, the breathable air is cooled by causing it to flow through a conduit in heat exchange relationship with a reservoir containing a liquid refrigerant medium which has a boiling point below the maximum desired temperature of the breathable air supply. The reservoir is vented to allow escape of refrigerant gas through an adjustable pressure relief valve, whereby cooling of the breathable air supply is effected through a progressive boiling away of the refrigerant liquid from the reservoir, the boiling point of the liquid being controlled by means of a corresponding adjustment of the pressure relief valve.

Abstract: Head mounting apparatus which can accommodate different head sizes and shapes comprises a substantially rigid member for supporting equipment, such as night vision equipment, to be used by the wearer, and a flexible member which can flex to adapt to the head of the wearer. The rigid and flexible members are connected by pivotal means at pivot positions along spaced pivotal axes. The flexible member has buttons for attachment of straps by which it is in use secured to the wearer's head. The position of the rigid member relative to the flexible member may be adjustable by manual rotation of knobs.

Abstract: A single stage demand valve for passing air from a cylinder of compressed air to a face mask includes a main valve member and a by-pass valve. The by-pass valve is provided to deliver air to the face mask should the main valve member stick or seize in the closed position. The by-pass valve is a constant pressure reduction valve, having a valve member in the form of a piston, whereby variations in air pressure in the breathable gas from the cylinder are compensated ensuring that the desired flow rate or air through the by-pass valve is maintained without repeated adjustment of the by-pass valve, as in the prior art.