Inogen G4 Columns:
The G4 Columns are basically filters. They help to remove the nitrogen and other element from the air, allowing the oxygen to be purified and delivered to you. These filters are technically known as "Sieve Beds". These filters are meant to be replaced regularly as needed. Your G4 Portable Oxygen concentrator will alert you when it is time to replace these filters with the "replace columns" notification. When this happens, you have a couple weeks to get your new Columns and replace them in your G4.
The G4 replacement columns come as a pair. Exchanging them when the time comes is very simple. So easy, that it can be done right at home in just minutes.