GB1530009A - Re-breathing apparatus - Google Patents

Abstract

1530009 Respiratory apparatus W B SHELBY 11 March 1976 09833/76 Heading A5T Respiratory apparatus particularly for use by divers comprises a facial breathing attachment 10 connected to a gas circuit supplied with a breathable gas mixture of oxygen and an inert gas, e.g. helium or nitrogen, from a cylinder 22 via a valve 41 which opens with increasing ambient pressure, the circuit also being connected to a cylinder 26 containing oxygen with little or no inert gas, via a solenoid valve 31 which is opened when the oxygen content of the breathable gas falls below a preset level to permit inflow of oxygen into the circuit whereby the oxygen content of the breathable gas remains constant. The valve 31 is controlled by means of transducers 34, 35 positioned in a chamber 32 of the gas circuit, the transducer 34 being responsive to total gas pressure and the transducer 35 to oxygen partial pressure. The outputs of the transducers are fed to respective amplifiers 52, 53 which are connected to a comparator 56 the output of which indicates percentage oxygen content of the breathing gas and operates the drive means 58 of the solenoid valve 31, the output being transmitted if the oxygen content falls below a pre-set value. The output of amplifier 52 reaches comparator 56 via a switch 70 having two positions corresponding to helium and nitrogen as inert gas. Switch 70 is also connected to a lamp alarm system 57 comprising lamp 76 which lights when oxygen content is too high, lamp 77 which lights when oxygen content is within permitted limits and lamp 78 which lights when oxygen content is too low. The oxygen partial pressure signal is also fed to a comparator (90 Fig. 4 not shown) coupled to a control setting maximum permitted oxygen partial pressure, the comparator (90) operating a solenoid valve (92) to shut-off oxygen supply from cylinder 26 if oxygen partial pressure is too high. A circuit providing a meter reading percentage oxygen content and total breathing gas pressure alternately, and a digital controller circuit therefor (Fig. 5) are described. The lamps 76, 77, 78 are conveniently arranged in a mask worn by the user. The gas circuit also includes a carbon dioxide scrubber 48 and a fan 49 or a diaphragm pump may be used to aid gas circulation. An additional oxygen partial pressure transducer 36 feeding an independent meter may be provided. "Logging" lines may be connected in the circuits to control a pen and paper recorder whereby operation of the apparatus is recorded. Manually operable valves 24, 28 may be provided in the gas circuit to permit the user to override the controls.