A portable non-electronic device intended to mix ambient air with compressed oxygen (O2) to generate a flow of oxygen rich air to a patient with adjustable inspired oxygen concentration (FiO2) [e.g., 28-100%] and adjustable flow rate, for continuous positive airway pressure (CPAP) with oxygen, during noninvasive and invasive ventilation (i.e., capable of both). Also known as a CPAP flow generator, it includes an oxygen supply connection, ambient air inlet, patient outlet, and controls for adjustment of both flow rate and FiO2. CPAP pressure is defined by the PEEP valve used with this device. This is a reusable device.