Abstract: A gas flow rate control device for a medical ventilator includes a variable-orifice valve for adjustment of the peak flow rate, and a waveform regulator which supplies controlled gas pressure to the orifice. The regulator maintains a fixed pressure differential between the upstream side of the orifice and a reference pressure. The reference pressure is variable between atmospheric pressure and a pressure which is essentially patient airway proximal pressure. When the reference pressure is patient airway proximal pressure, a constant pressure differential is maintained across the orifice so that a uniform flow rate is maintained. When the reference pressure is atmospheric pressure, a constant pressure is supplied to the upstream side of the orifice, so that the flow rate from the orifice decreases as patient airway proximal pressure on the downstream side of the orifice increases.

Abstract: A servo-type gas pressure relief valve for regulating air pump pressure to pneumatic components of a medical ventilator or similar equipment utilizes a small diaphragm-type bleed or pilot valve to control the action of a main diaphragm valve. A small amount of inlet gas from the bottom side of the large diaphragm is passed through a restricted orifice to the top side of the large diaphragm. The bleed valve bleeds this gas to the atmosphere at a selected pressure, said bleeding action creating a pressure differential across the diaphragm of the main valve, which is thereby opened to exhaust gas to the atmosphere. A screw adjustment exerts tension on a spring which, in turn, exerts a force on the upper part of the bleed valve diaphragm. By adjusting the tension on the spring, the pressure at which air is bled to the atmosphere can be controlled, thereby accurately controlling the pressure at which the main valve opens.

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.