Sciencemadness Discussion Board - Inside an oxygen concentrator

Inside an oxygen concentrator

Sulaiman - 5-11-2016 at 09:54

here is a domestic non-medical oxygen concentrator that no longer concentrates oxygen

motor driven change over valve ................ zeolite filters on top .................. air filters .............................. 240 Vac Input. Earth & Neutral direct, Live via switch and fuse

Where does the Earth wire go ? .......................................... Air pump (two in series)

I was surprised/disappointed to see how small the zeolite cylinders are.

No diagnostics yet ... just looking, thought others may be interested

Maker - 5-11-2016 at 14:28

It's probably "Double insulated", which means it doesn't require earthing. Look for the rating sticker, it should have a symbol that looks like a square in a square.

Does it still pump air?

Sulaiman - 6-11-2016 at 00:50

I have not looked at the label for the symbol but from the construction, there is no electrical path from inside to the user,
so I am not concerned.

Why bother with 3-core all the way to the plug ?
i) non-technical people satisfied by the presence of an earth wire in the plug ... with zero leakage current !
ii) technical people satisfied by the enclosure insulation
= worth the extra core ?, or just age related cynicism ?

I opened it because it appeared to be working perfectly normally,
but the output stream showed no more sign of oxygen than air.

So either the zeolite is 'dead', or the valve is not cycling, or something else

I'll look at it later ...

Maker - 6-11-2016 at 11:42

It's probably cheaper for the factory to buy a few thousand meters of three core because some other product requires earthing and use it on all their products than to buy smaller rolls of each.

Sulaiman - 11-11-2016 at 02:56

As far as I can determine, everything is workingexcept for the zeolite,
the pump pumps, the valve switches airflow, no leaks ......

HELP !

CAN ANYONE TELL ME WHAT GRADE OF ZEOLITE ABSORBS NITROGEN BUT NOT OXYGEN ?

AND WHERE TO BUY IT CHEAPLY ?

Chemetix - 11-11-2016 at 03:22

Do you need oxygen? And how much? I just made a water electrolysis cell that works really well, a zeolite absorber to concentrate O2 sounds like hard work to (replicate). Edit: source a consumable.

[Edited on 11-11-2016 by Chemetix]

Heavy Walter - 11-11-2016 at 05:42

Hi Sulaiman

Those oxygen generators are tricky. The normal operation includes adsorption/release under some specific pressures.

Wikipedia is not too explicit: On-board oxygen generating systems (OBOGS) and Oxygen concentrators use zeolites in conjunction with pressure swing adsorption to remove nitrogen from compressed air in order to supply oxygen for aircrews at high altitudes, as well as home and portable oxygen supplies.[10] (This reference has a broken link).

I have no info about the zeolite type but make sure that:
They are reactivated (probably the system includes that step).
The pressure cycle is completing its schedule.
Good luck!

Sulaiman - 11-11-2016 at 06:17

As far as I can tell, this oxygen concentrator is about as simple as possible, fixed timing - no oxygen% sensor

A little more research yielded the zeolite grade required ... 5A or 13x

The zeolite filters are very servicable, from the air-in end :
. end cap with four screws
. spring
. filter disk
. honey coloured balls (dessicant)
. filter disk
. zeolite
. filter disk
. end cap secured by four screws

Chemetix
I do not want to recreate one, just resurrect it.
I think that electrolysis is an expensive method of obtaining oxygen,
and the byproduct, Hydrogen, is not as suited to the domestic environment as Nitrogen

[Edited on 11-11-2016 by Sulaiman]

metalresearcher - 12-11-2016 at 00:03

Any ideas how much O2/N2 ratio these devices produce normally ?

I am currently after a discarded medical one which should considerably enrich the O2 content in the output.

Sulaiman - 12-11-2016 at 01:01

This model produces 90% O₂
'Medical' grade machines 95%+
Some of the silver activated zeolite manufacturers claim up to 99% (I think argon is the impurity)
and lithium based zeolites are available for higher gas flow rates per volume of zeolite

arkoma - 12-11-2016 at 06:02

I always kinda wondered how they worked.

Morgan - 12-11-2016 at 07:12

It's interesting that it uses Mickey Mouse pneumatic tubing, a convenient design for various projects.
https://www.google.com/search?q=mickey+mouse+aluminum+tube&a...

wg48 - 12-11-2016 at 07:52

Quote: Originally posted by Morgan

It's interesting that it uses Mickey Mouse pneumatic tubing, a convenient design for various projects.
https://www.google.com/search?q=mickey+mouse+aluminum+tube&a...

I would try to fixe it. It would be super usfull to produce oxygen enriched air for use with a gas torch.

unionised - 12-11-2016 at 08:15

Does this help?
http://www.vurup.sk/sites/vurup.sk/files/downloads/pc_3_2013...

andy1988 - 2-3-2019 at 08:32

Quote: Originally posted by Sulaiman

Interesting choice of compressor. I wonder what peak pressure they operate it at in this system.

Quote: Originally posted by RogueRose

On a completely different side note, i've designed an O2 concentrator (VERY high output 30-90LPM at 93-96% concentration) but unless I get help from someone to put it together and do some testing this will be put on hold. This is another product for glass blowers & welders.

RougeRose did you see this paper? Interesting that they point out the impurity in the oxygen feed would lower the efficiency of the furnace. Very interesting figures, like the pressure swing from 2 Bar(a) to 0.5 Bar(a) through a 30 second cycle (Figure 4). For cost savings they use just one bed instead of two, and use a centrifugal compressor instead of a reciprocating compressor.

Personally I'm interested in designing maximal energy efficiency at 5L+/min output, for that reason I'm interested in the AgA and LiAgX zeolites mentioned here. More energy efficient due to the smaller chambers, and the procedure to produce LiAgX from 13X doesn't look difficult! I expect the same for AgA but I hadn't seen a paper detailing a preparation of that yet.

What electronic valves are you using? These ones I'm finding on aliexpress have a minimum pressure requirement and are unsuitable for air below ambient pressure? Seems cost effective to use 3-way valves in a 2 bed design, and I don't think the little ones would be healthy for a centrifugal compressor. I'd expect a centrifugal compressor suitably sized for the pressure/flow with a 3mm inlet/outlet diameter would result in a drastic efficiency loss (time consuming to design these things, this is my hunch). So far the most suitable I've found is only 2-way for $10, 3-way for ~$21. I suppose 3D printing a valve, perhaps ceramic sintering/machining one is a route I want to go down anyway for substantial cost savings.

Which 13X supplier & silica gel supplier were you looking at? I did see this supplier ($99.25 for 25lbs, shipping $31), however this supplier ($98 for 25lbs, shipping $17 and no tax). However the latter appears to be a re-branding through a manufacturer that allows such drop-shipping given the artwork, vague product descriptions (intentional obfuscation I expect), and vague company details... identification of the original manufacturer may yield cost savings (I hate these supply chain games). My hunch is it's a 40+ year old U.S./Canadian manufacturer given these patterns. EDIT: Oh just found your thread on this. Also couldn't find any on TheCaryCompany, I need to call them, seems like something they would carry, their prices are reasonable if you buy enough stuff.

This was a fascinating read on the gas supply industry by the way (read: price fixing, and more!).

Are you interested in solar refrigeration? 13X & silica gel may be useful there as well (in case you ordered extra). Though I am leaning towards the domestic charcoal and methanol design/approach. Worth considering anyway.

[Edited on 3-3-2019 by andy1988]

I want to buy molecular sieves for my oxygen concentrators

Sulaiman - 3-3-2019 at 08:06

My second oxygen concentrator is now performing poorly.
so I have decided to refill both machines with new molecular sieves.
I will need 2x2x 250cc = 1 litre of molecular sieves.
My best guess so far is that type 13x is required.
eBay: China 500g = £15.48 incl. p&p, USA 450g = £18.08 plus £16.40 p&p
are alternatives to 13x available and affordable ?

Can anyone suggest a supplier for onr litre of mollecular sieves suitable for use in oxygen concentrators please ?