This invention relates to a gas pressure regulating valve for use in conjunction with underwater breathing apparatus.
Where the breathable gases supplied to a diver include a reclaimable gas such as helium, then exhaled gases are piped to surface apparatus for extraction of the reclaimable gas in a line at a lower pressure than the divers gas exhalation pressure. A valve usually termed a "gas reclaim" or "gas recovery" valve is used to isolate the divers breating space from the lower pressure in the gas reclaim line. One previously proposed gas reclaim valve is a single stage device having the disadvantage that the divers exhalation effort to operate the valve varies according to the pressure differential with the reclaim line. This disadvantage gives rise to discomfort in breathing; and moreover such a single stage device offers relatively little safeguard against the diver being subjected to reclaim line pressure (suction) in the event of a malfunction. Another previously proposed gas reclaim valve is a two-stage valve, but having the disadvantages of, first, being of unduly large physical dimensions and, second, having a relatively large number of moving components whose total mass is such as to demand undue breathing effort to operate the valve. Moreover, this valve is prone to malfunction in the event of ingress of foreign matter, particles, hair etc.
An object of the present invention is to provide a gas pressure regulating valve for use in conjunction with underwater breathing apparatus in which the aforesaid disadvantages are obviated or mitigated.
According to the present invention, there is provided a gas pressure regulating valve for use in conjunction with underwater breathing apparatus, comprising a first chamber disposed between a first shiftable wall member and a first fixed wall member for receiving exhaled gases, a second chamber disposed between a second shiftable wall member and a second fixed wall member, the first and second fixed wall members defining a third chamber therebetween for connection with a gas reclaim line, and a tubular duct extending from the first chamber to the second chamber through both wall members, said first shiftable wall member cooperating with an adjacent end of said tubular duct to constitute a first stage valve, and said second shiftable wall member cooperating with ports in said second fixed wall member to constitute a second stage valve.