Abstract: A demand valve for use in breathing apparatus, and comprising a housing 1 in which is mounted a diaphragm 2 such as to divide the interior of the housing into two separate chambers 3,4. Chamber 4 is vented to atmosphere through a hole 14; chamber 3 is connected via a pipe 13 to a gas outlet whereby breathing gas may be supplied to a face piece or mask for a user. Breathing air is supplied from a main gas supply channel 8 via a main valve 9,10 to a gas supply channel 6. A gas inlet channel 5 connects the supply channel 6 to the chamber 3 under the control of a needle valve 11 which closes an orifice 7. The head 11B of the needle valve is urged by a spring (not shown) into contact with the diaphragm 2 and thus the movement of the diaphragm controls the opening and closing of the needle valve. The diaphragm 2 is pivoted about spaced pivot members 15, and leaf springs 16 are used to maintain the diaphragm in contact with the pivot members 15.

Abstract: In a combined gas flow control regulator and pressure relief valve, the pressure relief valve includes a pressure relief member comprising a flange and a sleeve which is sealingly engaged with the piston rod of the gas flow control regulator and is slidable relative to the piston rod. A spring urges the flange of the pressure relief member into contact with the piston head of the gas flow control regulator thereby closing a gas relief aperture in the piston head capable of connecting a first chamber, which is one chamber of the gas flow control regulator to a second chamber which is a gas relief chamber from which gas can escape to atmosphere.

Abstract: A positive pressure filter respirator includes a full face mask comprising an outer mask 1 and an inner orinasal mask 2. A filter canister 5 is screw mounted to an air inlet 4, and a centrifugal fan 6, which is driven by a battery operated motor 7, is so arranged as to draw air through the filter canister 5 into the outer mask 1. The filter life and the battery life are extended by the use of a pressure responsive means which responds to the difference in pressure between the pressure in the interior of the orinasal mask 2 and the pressure in the space 20 within the outer mask 1 and outside the orinasal mask 2. The pressure responsive means reacts immediately to the commencement of either exhalation or inhalation to disable the fan 6 or on commencement of exhalation and to accelerate the fan 6 on commencement of inhalation.

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: 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.