The Inogen One G3 Portable Oxygen Concentrator uses a pair of sieve beds to seperated gases from the oxygen being delivered to you. The sieve beds should be replace every year to a year and a half deppending upon use to maintain a high level of oxygen concentration being delivered to the user. Your G3 will display a message saying “Service Soon” when it is time to replace the sieve beds. Once this message is received you have up to 30 days to purchase and install the new beds. Replacement is quick and easy and can be done by the Inogen One G3 owner right in the comfort of their home. Sieve bed carry a one (1) year warranty.