Abstract: An oxygen partial pressure controller regulates the oxygen partial pressure (PPO.sub.2) of the product gas of a pressure swing adsorption oxygen enriching system by means of a bleed valve which increases gas flow through the adsorptive system thereby decreasing the PPO.sub.2 of the product gas. The controller includes a solenoid valve which permits the bleed valve to function when the adsorption system pressure and PPO.sub.2 is high.

Abstract: An oxygen partial pressure controller regulates the oxygen partial pressure (PPO.sub.2) of the product gas of a pressure swing adsorption oxygen enriching system by means of a bleed valve which increases gas flow through the adsorptive system thereby decreasing the PPO.sub.2 of the product gas. The controller includes a solenoid valve which permits the bleed valve to function when the adsorption system pressure and PPO.sub.2 is high. An aneroid controls the product gas flow as a function of altitude when the bleed valve is permitted to function.

Abstract: A selector valve for an aircraft breathing system wherein oxygen enriched gas is provided by two sources, the primary source being fractionalized air and the secondary, backup, source being bottled oxygen is comprised of a control valve with three operating modes and a shuttle valve. In the first operating mode gas is provided from the primary source, in the second operating mode gas is provided from the primary source within certain operating parameters and outside these parameters gas from the secondary source is provided. In the third operating mode, gas from the secondary source is provided. The shuttle valve responds to the secondary source gas pressure and directs gas from either source to the pilot based on preset conditions.