Abstract: The invention provides a breathable gas regulator of the demand type for use with a low supply pressure (10 p.s.i or less) gas source.The regulator requires no greater demand effort on the part of a user than is required with present-day regulators of the same type which operate with much higher pressure (70 p.s.i. and above) gas sources, and it requires ducts, diaphragms and valves of no greater size than are required by present-day regulators. This is achieved by inclusion of a servo valve that is actuated by a fluidic amplifier arrangement responsive to the user's breathing pressure.In an embodiment of the invention particularly suited for use by an aviator, the regulator includes a pneumatically operated mixing valve arrangement for automatically varying, according to altitude, the proportions of, say, oxygen and air supplied to the demand valve of the regulator, and the mixing valve arrangement includes a fluidic gas concentration sensor.

Abstract: An environmental control system comprises a working gas circuit including a compressor-expander arrangement and first heat exchange means by which the working gas is conditioned before being passed to second heat exchange means connected in the circuit in heat exchange relationship with an environment to be controlled. The working gas is provided with means for regulating the mass of working gas in the circuit in response to the conditioning demand on the system. One such regulating means comprises an inlet path for admitting working gas to the circuit and an outlet path for removing working gas from the circuit.