Abstract: The valve assembly employs a peak flow valve with a first adjustable orifice which restricts gas flow through a conduit to establish a peak flow, a peak flow control for adjusting the size of the orifice, a separate valve which progressively closes a second conduit orifice in response to increases in the conduit pressure so as to achieve a desired decay rate for periodic gas flow, and a decay rate control which adjusts the initial closure of the second orifice. The valves are interconnected by means of a coupling which, in response to the decay rate control being adjusted, automatically adjusts the size of the first orifice by an amount sufficient to substantially compensate for changes in the peak flow rate caused by the decay rate adjustment.

Abstract: A valve assembly for mixing air and oxygen in a medical respirator over a wide range of volumetric flow rates, without sacrificing relative mixing accuracy at the lower flow rates. The assembly is divided into a plurality of mixing valve modules characterized respectively by progressively increasing volumetric flow capacities and progressively decreasing absolute mixing accuracies. The higher flow capacity modules are sequentially brought into operation as the overall valve flow increases and then interrupted when the flow decreases below a threshold level associated with each module. The valve assembly accordingly has a large range of flow capacities without degrading absolute mixing accuracy during low flow rate conditions by the effect of the higher capacity modules.