I have a Phillips Respironics Everflo 5 liter oxygen concentrator for sale. This is in excellent condition and has no cosmetic flaws. It runs so quietly compared to the Invacare Perfecto 2 machine, and it is much lighter in weight than the competition. I have personally checked the oxygen purity level and it exceeds 90% pure oxygen which is fantastic. I will gladly perform the test with my oxygen analyzer for you in person. I have one other oxygen concentrator machine available as well. See my other listing for it. Pick up in Murfreesboro, Tennessee.