Valves and breathing apparatus incorporating such valves

Claim 1

A breathing gas demand valve comprising means defining an inlet chamber for receiving gas from a breathing gas supply; means defining an outlet chamber for delivering gas to breathing interface means; valve means provided in the gas flowpath between said inlet and outlet chambers and constructed and arranged to control the main gas flow through the valve from the inlet chamber to the outlet chamber; means defining a control chamber adapted to have a gas pressure therein; said valve means being responsive to the gas pressure in said control chamber whereby said main gas flow is controlled by said valve means responsive to the gas pressure in the control chamber; an inlet orifice connecting the control chamber with the inlet chamber and through which gas is substantially continuously bled from the inlet chamber to the control chamber; an outlet orifice connecting the control chamber with the outlet chamber and through which a jet of gas is substantially continuously vented from the control chamber into the outlet chamber; a pressure-responsive member bounding on one side thereof the outlet chamber and exposed on the other side to a reference pressure, said pressure-responsive member being constructed and arranged to deflect in response to pressure changes within the outlet chamber consequent to the respiration of a user of the valve; and a control member which is distinct from but coupled to said pressure-responsive member, and located within the outlet chamber; the control member comprising a two-armed, spring element a first arm of which is held firmly to a fixed part of the valve structure and the second arm of which is coupled to the pressure-responsive member with a portion of the second arm lying adjacent to the outlet orifice in the path of the jet of gas vented from the control chamber through the outlet orifice; the second arm of the control member being deflectable relative to the first arm about a flexural pivot established in said control member and arranged to deflect with deflection of the pressure-responsive member to move the said portion of said second arm towards or away from the outlet orifice in dependence upon pressure changes within said outlet chamber, thereby to control the rate of venting of gas from the control chamber and thereby the gas pressure within said control chamber; the control member being so constructed and arranged that the aforesaid movement of said portion of the second arm thereof controls the rate of venting of gas from the control chamber by variable interaction with said jet and is arranged to establish such gas pressure in the control chamber as to shut off the main gas flow through the valve without said portion of said second arm seating physically over said outlet orifice; the control member being self-biasing, resiliently, towards a position in which said portion of the second arm thereof is at a set spacing from said outlet orifice; and means associated with said first arm and said valve structure for applying a variable force to a portion of said first arm to vary said set spacing between said portion of said second arm and said outlet orifice.