Room air is drawn via a small electric compressor into the concentrator through a series of filters. This compressed air passes through 2 small molecular sieve beds which remove the unwanted nitrogen. Any waste gas is harmlessly returned to the air and the process repeated. The oxygen is then stored in a reservoir for the patient to breathe via either a nasal cannula or mask. The flow meter enables oxygen flows of 0-5 litres per minute to be delivered. An uninterrupted supply of oxygen, as when required is available at the touch of a button.