US 4,072,148 AGranted

Multistage mixing valve for a medical respirator

AssigneeBourns, Inc.

InventorsRamon J. Munson, Claude C. Hurd, James Weigl

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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.

Claims9

Dependent claims

A valve for accurately mixing gases from a plurality of separate gas source means over a range of volumetric flow rates, said gas source means each being characterized by nominally equal but fluctuating pressure levels, comprising:

a plurality of serially arranged mixing valve modules, each respective module including means providing a greater volumetric flow capacities and a lesser absolute mixing accuracy than the preceding valve module, each of said modules including a plurality of inlet ports each adapted to receive a gas from one of said gas sources, an outlet port, and gas mixing means between each said inlet ports and said outlet port for controlling the ratio of said separate gases flowing through the module, each outlet port of each module being mutually coupled to provide a single valve outlet,
means for adjusting the mixing ratio of each of said modules by substantially equal amounts, and
for each of said modules other than the module having the lowest flow capacity and highest absolute mixing accuracy, means for permitting gas flow through said module until the total volumetric gas flow through said valve exceeds a predetermined threshold, the threshold level for each module varying in positive proportion to the volumetric flow capacity of said module.

In a medical respirator having nominally constant-pressure air and oxygen sources, conduit means for delivering gas from said sources to a patient, and control means controlling the supply of gas from said sources to said conduit means, wherein the improvement comprises a two-stage mixing valve for accurately setting the air/oxygen mixture of breathing gas delivered to the patient over a range of volumetric flow rates, despite fluctuations in the actual pressures of said sources, said two-stage valve comprising:

first and second mixing valves, each of said mixing valves including air and oxygen inlet ports adapted to receive gas from said sources, an outlet port adapted to be connected to said conduit means, and means for controlling the air/oxygen mixing ratio, said first mixing valve having a greater absolute mixing accuracy but lower volumetric flow capacity than said second mixing valve,
means for adjusting the mixing ratios of each of said mixing valves, and
means between said second mixing valve outlet port and said conduit adapted to sense the pressure in said conduit means and interrupt gas flow through said second mixing valve when the sensed pressure exceeds a predetermined threshold level indicative of a low gas flow condition,
whereby said first mixing valve acts alone during low flow rate conditions to achieve a high absolute mixing accuracy when the pressure differential across said mixing valves is relatively small, and said first and second mixing valves act together during high flow rate conditions to achieve a lower absolute but comparable relative mixing accuracy when said pressure differential is relatively high.

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Dependencies are inferred from the claim text.