Ive said this in a few other posts. Everyone seems to get some use from it, so here it is again:
There are a wide range of concentrators out there. Heres is a quick shakedown of what you may be able to buy:
Assuming all concentrators are rebuilt properly:
-Airsep Newlife: Last about 12k hours, no real filters to keep contaminants out of the system. Sieve beds tend to get contaminated easily from lack of filters, and will harm purity in the higher flow rates. Should put out about 8-9psi which is good. Pretty noisy valves as they age.
-Invacare Mobilaire 5: Last between 20-25k hours. Many many HEPA filters to keep the system very clean. Sieve beds are very very resilient and hardly ever go bad. Put out mid 90% o2 at all flow rates for a very long time. Factory PSI is 5 or 6. Quiet machine.
-Healthdyne Alliance: Lasts about 20k hours also. Good filtration. Sieve beds are very resilient. WHISPER quiet! 96% purity at 5LPM is very common. Factory is 5 or 6 psi.
-Devilbiss MC-Series; Solairis 505/515- Last about 20k hours also. Great filtration, pretty quiet. Good purity. These machines chug along at 8-9PSI from the factory with no problems whatsoever.
Respironics Millenium: When you get one that works, they are good...for about only 8k hours. "Fewer moving parts" doesnt always mean reliability. There is a reason they are on ebay for $100 AS IS. They are pretty quiet. 6PSI output pressure.
Unless you buy a new concentrator, these are the " main contenders" for used oxygen concentrators now. Anything else you may find, ask the seller all the same questions you just asked and you *should* be able to get an intelligent response if they service the equipment.
Also, and if you want to take ANY guesswork out of the purity your concentrator is putting out, get one with an oxygen monitor (OCI/OPI). If the "Normal Oxygen" light is on, you know it is maintaining at least 87% oxygen! Unless it has the "OCI" feature, no series of beeps, clicks, wooshes or anything else from a standard concentrator will let you know the purity is good, unless there is a decent warranty and they stand behind their work.
Ive read a lot on here that a concentrator doesnt have as much "oomph" as tanked oxygen because they dont put out the same purity. This statement is true. Tanked oxygen is 97.8% pure. An oxygen concentrator that has been PROPERLY rebuilt, will put out around 95% oxygen at 5 Liters Per Minute. Not a huge loss at all!! If you have a concentrator that is running "ok" at 3 or 3.5 LPM, bump it up to 5LPM. If there is a noticeable loss in torch power, its probably because the concentrator isnt operating properly at high flow rates like it should. Once you get it running properly at 5LPM, you will never look back
If you are going to be using Boro a lot, then you will probably need two oxygen concentrators. I would recommend the Devilbiss Solairis 505 Model. It is a 5LPM Concentrator, and puts out 8-9 psi which is among the highest out of all the concentrators available.
There is also the option of an Oxygen Generator. They are a little bit bigger, but put out more LPM (amount of oxygen) and higher PSI (pressure of output oxygen). I have sold, and know of many more people that are using OGSI's OG-15 Oxygen Generator and love it!
I hope this helps you with your search!