Just jumped on the oxygen generator bandwagon.
Thanks for all the posts everyone, it solved my problem of international commercial travel.
Can’t fly with tanks anymore, so this should do the trick.
The numbers (above by zuutroy) are very interesting. I sort of knew the o2 purity is not that great, with ~80% being the theoretical limit, because they work purely by removing nitrogen, and nitrogen is about 80% of the air, and you will never (easily) remove all of it. So 70% is pretty good going for 1 litre per minute. From my old writeup
The FAA requires that all pilots flying their aircraft above 12,500 feet for 30 minutes or longer or at 14,000 feet or above during the entire flight must use supplemental oxygen – ref FAR 91.211. Passengers must have oxygen available (but don’t need to use it) above 15,000ft. The amount required (reference: FAR 23.1447) is 1 liter of oxygen per minute for every 10,000 feet. For example, at 18,000 feet there should be a flow of 1.8 liters per minute of oxygen available via a standard breathing device. The FAA requires there should be a device so attached to each breathing device that visually shows the flow of oxygen. The FAA also recommends that oxygen be used at night at altitudes over 5,000 feet.
So at FL180 you should be fed with 1.8 litres per minute. However that is based on
Demand regulators, which generate an oxygen pulse at the start of each inhalation cycle, are a lot more efficient than contact flow. Also Lionel’s links above show much lower numbers than 1.8 litres per 10k feet. So it’s a bit confusing… also a demand regulator like the MH O2D2 needs a fair bit of pressure to work; typically 20psi. I don’t know if these oxygen generators manage that.
Well SeQual claim 90% at 3l/min. An orange light comes on when purity drops to 70-90% and a red light when less than 70%, and that tallies with my measurements. The zeolite has shed about 3-5% of its weight after baking (there are two different mesh sizes). I have one more batch to do tomorrow and then I’ll see if it improves things.
Yes, I am wrong with my 80% being the theoretical limit. If you remove all nitrogen, you end up with highly pure ogygen. Only about 1% of the air is not oxygen.
The zeolite should get continually recycled during operation. Does it “wear out”?
Where does the high power consumption of these generators come from? Do they heat the zeolite?
The pressure swing adsorption cycle does indeed recycle continuously but only the nitrogen. My suspicion is that the one I bought is down on efficiency because of water adsorbing to the zeolite during storage. The seller said it was working fine when it was last used but when he got around to selling it the error lights were on. Power consumption would be mostly down to the 120 W compressor that forces the air through the sieve beds.
zuutroy wrote:
My suspicion is that the one I bought is down on efficiency because of water adsorbing to the zeolite during storage.
You can desorb water from the zeolite by heating it to approx. 250°C in vacuum for several hours.
Ultranomad wrote:
You can desorb water from the zeolite by heating it to approx. 250°C in vacuum for several hours.
Yea I did that. Sadly the story didn’t end well and my bargain Eclipse is for the scrap heap. Didn’t work at all when put back together. I think the sealed zeolite unit isn’t really made to be tampered with. New plan is just BOC medical oxygen cylinders with built in regulator through work and pay for the tea and coffee to make up the cost 
Peter wrote:
Demand regulators, which generate an oxygen pulse at the start of each inhalation cycle, are a lot more efficient than contact flow. Also Lionel’s links above show much lower numbers than 1.8 litres per 10k feet. So it’s a bit confusing… also a demand regulator like the MH O2D2 needs a fair bit of pressure to work; typically 20psi. I don’t know if these oxygen generators manage that.
So, the idea of the lightest of these machines is that they are in some way their own “regulators”. They issue a puff of oxygen during one’s inhalation cycle. However, I discover that some portable machines can also deliver a continuous flow, see https://www.oxygenconcentratorstore.com/continuous-flow-portable-oxygen-concentrators/ for a (partial?) list. According to https://www.oxygenconcentratorstore.com/sequal-eclipse-5/, the Sequal does continuous flow at 3l/min and has an outlet pressure of 5.0 psig. According to the Unix “units” program, 5.0 psig is 19.7psi… Here’s what they say about that:
Gauge pressure functions
Gauge pressure is measured relative to atmospheric pressure. In the English system, where pressure is often given in pounds per square inch, gauge pressure is often indicated by ‘psig’ to distinguish it from absolute pressure, often indicated by ‘psia’. At the standard atmospheric pressure of 14.696 psia, a gauge pressure of 0 psig is an absolute pressure of 14.696 psia; an automobile tire inflated to 31 psig has an absolute pressure of 45.696 psia.
One way of understanding this is that what the unit can do is deliver 5.0psi above ambient pressure. 20psi at sea level, but only 12.5 psi at FL150?
Yes; PSIG is the differential pressure above ambient.
Oxygen concentrators work by pumping air through zeolite crystals which absorb much of the nitrogen. So you have an air pump of some sort in there, and that has to be working differentially. It won’t be a gear pump with a spring loaded relief valve after it, like the electric backup fuel pumps in our engines.
So at say FL180, when the air is down from 15psi to 7.5psi (500 millibar) the machine will be delivering half the sea level oxygen mass flow. Whether that is enough, who knows? It might be. Certainly better than nothing.
Whereas the 1st stage reg on an oxygen cylinder delivers an absolute pressure. Well, I think it does. A very good Q.
