Abstract: An oxygen delivery apparatus includes a pneumatic conserving device which uses a portion of gas exiting its main valve to interrupt delivery of the gas. Gas is dispensed upon inhalation and is interrupted by means of suitable pneumatic connections between the device's delivery system and its sensing system. In some versions, the apparatus comprises an oxygen concentrator and the conserving device operates to deliver oxygen generated by the concentrator upon inhalation, and interrupts such delivery substantially independently of exhalation.