I purchased a RESPONICS EVER-GO portable air concentrator. I have very severe COPD. It advertised it's capacity as up to 5 LPM. I require this upon exertion, talking, walking, etc. The warranty stated that I had 10 days to return it if it did not suit my needs. An alarm went off all the time stating it was not able to put out the amount of oxygen I required. They said to give it a couple of days to self adjust . HA. All they were doing was running the clock. BBB stated customer remorse. I had to pay 600 restock fee.