O2 concentrator question

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good friend

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Mar 18, 2024, 1:23:30 PMMar 18
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Anything new about oxygen concentrators these days ?
  (now that covid came (and went?) )
I'm thinking on looking for one instead of a tank for O2 and would love
hearing any recommendations or suggestions or info. about modern
developments.
My most heat intensive use would be melting brass/braze out of lugs to
replace tubes  ...   so one sized to deliver a noticeable amount of
O2...    "portable" would be best.

noMadic  Thomas

Doug Fattic

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Mar 19, 2024, 12:43:55 PMMar 19
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I don't know anything about newer oxygen concentrators that are designed to allow a person with breathing difficulty to be mobile.  The ones we use for brazing were designed I suppose for someone bedridden.  For some the unit is placed in another room next so their noise isn't bothersome and a long hose can reach the patient.  I'm just guessing but I would think these older bigger units are preferable for brazing because they have more output.  They aren't that big that their footprint would not be much of an issue. 

I have several oxygen concentrators I've picked up over the years.  My 1st one that I still mainly use is a DeVilbiss model 515.  I bought it refurbished from M&M Medical in Beaverdale, PA.  It cost me $300 and came with a 3 year guarantee. I recommend others do this too because they eventually save money and the hassle of getting a refill.  They are just very convenient.  My backup is another DeVilbiss that is a later model 525.  It is black instead of beige.  I also have a couple of Invicare Platinum models.  They work just fine but - even though the DeVilbiss and Invicare are both rated as having the same 5 lpm output - the Devilbiss has greater output.  That comes in handy if I am using a rosebud.  M&M Medical says the Devilbiss and Invicare units have a better repair record than other brands.

Of course some of my students have found good concentrators for $50 to $100 they bought from someone that works in a nursing home and became available when someone died and their estate didn't want to be bothered with them.  While these good deals exist, it takes some luck to find them and $300 for a refurbished one seems like a reasonable cost.  Of course they are probably more expensive in 2024.  I check Craigslist for them from time to time and seldom do I see a price as low as $300.  It helps to live in a big metropolitan area for great deals.

Doug Fattic   
Niles, Michigan

good friend

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Mar 20, 2024, 1:50:48 AMMar 20
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thank you for this interesting/useful response!
   noMadic  Thomas

Jim Adney

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Mar 20, 2024, 9:22:46 AMMar 20
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I've never used an O2 concentrator, but the concept intrigues me.

What pressure will they compress to, or does it vary by model?

If it varies, then what range of pressures?

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Jim Adney, jad...@vwtype3.org
Madison, Wisconsin, USA
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Doug Fattic

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Mar 20, 2024, 1:20:07 PMMar 20
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Jim, a concentrator takes out of the air the nitrogen and carbon dioxide as it is flowing through the unit and just leaves mostly pure oxygen (92% or 93% if it is operating properly) coming out of the output.  You adjust the volume of O2 flow with a knob on the front of the unit.  There is a ball in tube (that can move up and down) showing the amount of flow that is regulated by that control knob.  You don't control the pressure just the amount of flow.  This is obviously related to the size of tip you are using.  This is a huge safety issue because, unlike a tank, it is not pressurized and won't become a uncontrolled missile if knocked over and the regulator comes off.  Welding supply stores often have pictures of the destruction caused by a flying tank when the valves on top gets broken and the tank gets lose. 

An advantage of a Devilbiss is that their outlet fitting is a brass size B the same as a welding hose.  It is possible to screw the end of your welding hose directly into the concentrator's output fitting.  Other units like the Invacare brand use a barb output fitting.  There are plastic convertors that have a barb on one end and a B fitting on the other that can make it possible to attach a welding hose to the concentrator.  Of course a small clear hose has to be placed between the 2 barbs.  While this is not really a problem, it can be an inconvenience so why not avoid it and just buy a Devilbiss?

Some apartments or home or shop insurance regulations do not want oxyacetylene units because of liability.  However using a BBQ propane tank and an oxygen concentrator avoids the problem.  BBQing is too popular to regulate against so this combination works well for those in bigger cities and not out on the farm where nobody cares.  

If one did not inherit or already have an oxyacetylene unit getting a concentrator and torch set up for propane is the sensible approach.  In fact even if one already has an oxyacetylene unit, it still makes sense to change both over because of cost, convenience (propane is MUCH cheaper than acetylene) and safety.  

Doug Fattic encouraging the use of a concentrator and propane for brazing in
Niles, Michigan   

jim g

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Mar 20, 2024, 6:58:58 PMMar 20
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I've got a couple of additional comments to add regarding oxygen concentrators:

1. Be wary of portable machines, and/or machines that state they operate in "pulse mode".  What this means is that they don't produce a steady stream of oxygen, but instead output it intermittently...you can imagine how this might affect a torch.

2. If you're going to run a rosebud or a bigger torch, get a machine that will output 10 liters of O2 per minute (LPM).  Most of the common models used for medical use output 5 LPM, which is certainly enough for a torch, but might not be enough for a rosebud.  YMMV.

3. Most machines have a small containment tank (~ 1 liter) that contains pressurized O2, with a cheap plastic regulator on top.  This means that, while the machine might be rated for a flow rate of 5LPM / 10LPM / etc, you can tweak the pressure somewhat.  Of course, there is no included pressure gauge, so you either have to guesstimate, or attach your own gauge.

4. These machines have inlet filters that need to be cleaned and/or replaced periodically.  Make sure that you can (still) get parts for a machine before you spend $$$ on one.

5. Often you can find the service manual for a machine if you poke around online.  This can be super-helpful for diagnostics/repair/maintenance.

Thanks!
-Jim G


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Doug Fattic

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Mar 29, 2024, 7:03:00 PMMar 29
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Just for reference, I am able to use both my Paige and Meco rosebuds with my DeVilbiss model 515 concentrator.  I'm able to take apart a standard steerer and crown assembly without any issues using one of those rosebuds with that concentrator.  I don't have any trouble using those rosebuds on any other joint either.  Having said that the DeVilbiss does not put out as much oomph as if I was using my oxygen tanks but it works just fine.  I think I read somewhere that the DeVilbiss model 515 or 525 really puts out 8 lpm instead of just 5.  I've tried several other 5 lpm oxygen concentrators and they have less output.  Those other models all work okay with standard propane tips but have trouble keeping up with a rosebud. 

M&M Medical told me over the phone that a 10 lpm unit is more prone to need repair and of course cost more to begin with.  I've never tried one myself so I don't have any personal opinions.  I did try to put two 5 lpm units together on one line.  They sort of cancelled themselves out if their output was joined on a T junction but worked okay (at least in my experiment) if the 2 tubes came together on a Y junction.  I probably needed to use a bigger tube after the junction. I never really bothered to work out any bugs of using 2 units together because all my brazing could be accomplished using just one DeVilbiss 5 lpm unit.  

I've never found any need to use my oxyacetylene unit for any reason other than to show framebuilding class students how it works.  This includes fillet brazing too.  I highly recommend using propane and an oxygen concentrator for both cost and convenience.  And I think it is easier for a beginner to use propane over acetylene.  I don't feel like I gave up on anything  when I made the switch.  It is possible that those raised and trained on oxyacetylene might find an adjustment to the learning curve and there is no need to switch when they have already mastered acetylene.  

Doug Fattic
Niles, Michigan   
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