oxygen concentrators

[Doug Fattic]

An oxygen concentrator might be one of the options to consider when buying a brazing outfit. For those not familiar with them, they are the units that supply patients (usually elderly ones) with nearly pure oxygen when their lungs are no longer working at full capacity. They are a small machine about the size of a suitcase that separates out the nitrogen and carbon dioxide in the air to supply nearly pure oxygen (pure enough for brazing anyway). They have a clear plastic hose that runs to a patient’s nose. They are heavily regulated in the medical industry and cost thousands of dollars if buying them outright or rent for hundreds a month. However there are used ones sold on the open market at modest prices for non-medical purposes like glass flame-working or brazing. They are popular with those that make jewelry.

Someone might consider this option is for reasons of safety, convenience and cost. Because it is not a highly pressurized tank, it isn’t going to turn into a missile or bomb if something goes wrong. There is no need to transport them to the store for refills (only possible during open hours) and the cost to run them is only the electricity they use and an occasional filter change. Because they have a built in flow meter, they don’t require a regulator saving that expense. Their biggest disadvantage is that they have to run for a minute or 2 before they produce enough pure oxygen or it will blow out the flame.

Probably the biggest market for concentrators is for people that live in big cities where the purchase and transport of oxyacetylene tanks are restricted or are a long way from a welding supply store. Furthermore some rental or home insurance policies are not friendly to potentially hazardous tanks. This unit solves those problems.

They are made with various amounts of oxygen output. The smallest ones at 5 liters per minute work fine with torches usually used for brazing. Their units of life is measured in hours used and designed to run for several years continuously.

There are many companies that sell refurbished ones. I bought mine from M&M Medical Repair in Beaverdale, Pennsylvania. They have all kinds of makes and models in stock. They are a supplier to other retailers as well. A 5 lpm unit costs $300 and comes with a 3 year warranty. I paid $30 for shipping to Michigan. The Rio Grand Jewelry company (they have online sales) sells a brazing version for $425. DotMed.com is an auction house for all kinds of medical equipment including concentrators with hundreds advertised at various prices. It is common to find them in the classifieds for $75 to $200.

Oxygen concentrators don’t typically need to be modified for brazing. On mine, the oxygen output has a brass size B fitting. All I need to do is plug it in, screw the end of my hose onto the fitting, turn it on and wait a minute or 2. After I light the flame, I adjust the flowmeter so its output matches the orifice size of the tip.

Concentrators differ a bit on what kind of fitting is at the end of the output. They have some kind of plastic barb to hold the clear hose that carries the oxygen to the patient. On my Devilbiss unit that plastic barb unscrews from a brass B fitting. The same fitting that is on the output of a oxygen regulator. On other models that only have a plastic non-removable barb, one would have to make a transition piece to convert the plastic ending into a brass A or B welding hose fitting. That could be done with a brass unit from Western Enterprises that has a barb on one end that fits into a short piece of clear hose and an A or B fitting on the other to connect to a hose going to your torch.

I want to be clear I’m not suggesting a concentrator is the best way to go for everyone. What I am saying is that it is a very good option to consider for safety, convenience and cost reasons. It combines nicely with propane that can be chosen for the same reasons. We are all different in what we like or don’t. And our choices can be influenced by where it is most convenient to buy what we want.

Doug Fattic
Niles, Michigan

[shirk]

Doug's info on using a concentrator with propane was the tipping point for me finally buying a brazing rig. I've been wanting to build a few frames for years but had not bought the needed supplies. I was watching craigslist for a used brazing set-up but they were all huge torches or more than I initially wanted to spend.

Thanks again Doug for sharing all your hard earned info.

[David Tollefson]

That's the same oxy concentrator unit that I have. Never a hiccup. Like you, it was what made it so much more accessible for me. I owe a great debt of gratitude to Doug for all the information he's shared.

Doug, if you're ever in the Seattle area, ring me up. I owe you a round or two.

[Jonny Cycles]

Doug,

Thanks for all the great info on oxygen concentrators. I just went through the process of getting a new torch and tanks and referenced this thread - http://www.velocipedesalon.com/forum...ane-30480.html extensively while doing so. I was interested in the idea of an oxygen concentrator, but the flow rate became the main sticking point for me.

My previous setup was oxygen propane. After starting out using a smaller tip I quickly gravitated to using a larger tip, in fact ultimately settling on the largest tip I could find which was a tip with a 0.125" opening, and sometimes a rose bud. I often ran them both at the max flow of propane and oxygen I could get w/out the torch blowing out. (ok ok....I turned it down a bit for bottle mounts and cable guides). Would I wish this tip size on a newbie? No. Is this size required to build a frame? No. Is a bigger flame better? It's debatable, but it worked better for me. Others may not have the same experience but I know many builders do prefer a large tip.

My point is: Consider having the ability to run large tips. If not now, maybe sometime in the future at least to try it. The book that comes with my Smith AW1A torch doesn't give the oxygen flow rates for a oxy-propane setup with a 0.125" tip or a rosebud, but it does list the oxygen consumption for a 0.106" tip used with propane: 38 scfh, or 17.9 LPM. While 20 LPM concentrators are available, they are a bit of an investment.

Acetylene makes it a bit easier. For acetylene I would want the ability to run at least a 0.06" tip. The oxygen flow rate listed for these is a bit more reasonable at 8 LPM. 10 LPM oxygen concentrators are easier to find and quite a bit less expensive.

[Doug Fattic]

Jon, you bring out important points on the output of an oxygen concentrator and tip size preferences. This morning I went out to the shop and tried using large tips with my concentrator to find their limits. I have a Smith AW1A torch handle. This is a small “aircraft” size torch handle. I attached the AT-61 mixer elbow designed for propane (the AT-60 is for acetylene) that has a threaded end that allows for different sizes of tips to be exchanged. I put on a NE154 tip that is marked 36. This 36 number represents the drill size 36 which has an orifice of .1065”. My oxygen concentrator is a DeVilbiss model 515s and has a stated output of 5 liters per minute. In actuality I bought a DeVilbiss because others have indicated its actual output is closer to 8 lpm. It worked okay but the concentrator was at its limit of supplying enough oxygen. In fact if I turned up the propane beyond what is intended for that tip size I ran out of oxygen. At that volume it sounded loud like a jet engine. I didn’t like the the shape of the cone of the flame. It was like a frayed bulb on the end.

I also tried the oxygen output with my Victor setup. In this case I used their acetylene W-J-6 welding nozzle with propane as the gas. The Victor size 6 tip is also .106” in diameter. Just for clarity this is an all-in-one unit that does not have interchangeable tip possibility. You change the whole unit from the torch handle if you want to change tip size. The mixer part of this unit is more like a propane one in that it has 6 supply holes just like their UN-J mixer elbow designed for propane. For comparison purposes a W-J-4 has 4 supply holes. Obviously there is more oxygen needed to match the larger amount of burnable gas with a bigger tip. Neither the Smith NE154 tip (which is designed for propane when using it with the AT-61) or the W-J-6 (which is designed for acetylene) has the recess on the end of the tip that helps keep a propane flame attached like what is on the Victor TEN tips (to be used with their UN-J mixer elbow) or the propane tips made by TM Technologies specifically for propane that fit the Meco Midget torch handle. However if you carefully adjust the flame they still work okay. This flame pattern on the W-J-6 was very nice and pointed. Again my concentrator supplied enough oxygen but it was at its limit.

As Jon has pointed out, some pros prefer a big tip/flame for brazing. They can get in and out with their huge flame very fast. The advantage is that the heat effected zone going up the tube is minimized because it takes less time to braze a joint. A big flame can also reduce alignment distortions. I have found that it is not possible for 99% of beginners to use a very large tip. Things happen too fast for them to recognize how to respond quickly enough. However too small a tip can be problematic too. That requires a more precise heating pattern and many have trouble heating something like a lug evenly if the flame is small. For several reasons I don’t like using a big flame and prefer something like a Victor #3 for lug brazing. This is just personal preference and isn’t related to better or worse.

In summary, my DeVilbiss 515s rated as 5 liters per minute (but actually has a higher output) can run a tip orifice size up to .106” (a Victor #6). The actual limit is a Victor #4 if the propane is tuned up to maximum. If an experienced brazer like Jon wants to use bigger tips, they would need to get a bigger concentrator or use acetylene with a smaller concentrator or use oxygen tanks.

Just for a reference point. I prefer a Victor #4 for bottom bracket shells and fork crowns when using propane. Students do better with a #3. I typically use a #3 when doing lugs and dropouts. For Braze-ons I use a #2. And I’ve found I have better control with a #1 tip then a #2 when fillet brazing with propane. In fact tip size doesn’t make too much difference with me because I can make adjustments with whatever.

Doug Fattic
Niles, Michigan

[bambuko]

...In summary, my DeVilbiss 515s rated as 5 liters per minute (but actually has a higher output) can run a tip orifice size up to .106” (a Victor #6)...

Doug, from when I was doing my reasearch on the subject I seem to remember that flows higher than nominal were less pure oxygen?
So you might be getting 90% oxygen at 5 lpm, but less than that at higher flow?

[jclay]

Are any of you using a Meco Midget with an oxygen concentrator? I've noticed that driving a #4 or 5 tip hard enough for crowns and such requires at least 12 psi (ox/acetylene). Use of LP required higher pressure. While industrial oxygen concentrators can be driven at adequate pressures I don't know if the typical home medical device has the capability. Maybe some one here has crossed that bridge.

Both of my Midgets require similarly high oxygen pressure where my AW1A drives similar flames at perhaps 4 psi, oxygen. It doesn't matter with compressed gas cylinders but it might be an issue with inexpensive oxygen concentrators.

If you think you'll ever use a cutting attachment, maybe to cobble together a vise pedistle from scrap as I did, even higher oxygen pressures and flow rates will be necessary.

Don't take this as anti-concentrator, just information that might be relevant to particular situations and goals.

[Mark Kelly]

I did some work investigating using oxygen concentrators for our yeast propagators. The application requires a reasonable flow rate and head pressure (about 10 litres / minute at 200 kPa IIRC) so I tracked down some units with that capability. You are right, 90% of the available units are low pressure only.

I notice that our nitrogen generator (which is just an oxygen concentrator run the other way around) runs all day at 500 kPa, so it should be possible to hack a home oxygen concentrator by increasing the feed pressure. On the other hand, I can't think of a better way of voiding your insurance.

[devlin]

The biggest hurdle, once again for us southern hemispherers, is cost. I googled around and spoke to a number of companies here and I couldn't find anything for less than $1k and it was iffy if it had actually been serviced. Any of the US companies lost interest when I aksed about shipping to Australia. So far I have an oxy bottle but want to get the concentrator. Where did you find a supply of them Mark and how much were they?

[nspace]

Doug's posts here (and elsewhere on the web) have been invaluable. Particularly for someone who wants to dabble in this stuff with a small setup for home use. So thank you for writing such thoughtful and detailed responses! Your success as a teacher definitely comes through in your words.

With the advice in the other thread I successfully put together a setup using a Healthdyne Alliance 505, it outputs 5 LPM which seems to be sufficient for the time being. Of course, aside from practice pieces I don't have much to show for it. Once kids arrived its been either use the limited time available to ride my bike and stay in shape or wake them up playing with tools in the basement :) Hopefully I get more opportunities soon so experiment more, but it has seemed to work really good for silver brazing lugs, and even a bit of brass work. I hope one day I can attend a class!

[waterlaz]

Doug, from when I was doing my reasearch on the subject I seem to remember that flows higher than nominal were less pure oxygen?
So you might be getting 90% oxygen at 5 lpm, but less than that at higher flow?

When I wanted to buy an oxygen concentrator, I had looked at one model that promised 5 lpm of oxygen output. However, at this flow rate the purity of oxygen dropped to 50-60% according to the manual.
The next better model was twice as expensive, so I gave up on the idea.

[David Tollefson]

I'll have to look at the bubble gage when I've got the flame set, but I don't think I'm anywhere NEAR the 5LPM flow rate max when I'm brazing, even with the #4 tip. Probably more like 2. Or else I'm doing something grossly wrong. But the fillets are doing just fine.

[Doug Fattic]

When I wanted to buy an oxygen concentrator, I had looked at one model that promised 5 lpm of oxygen output. However, at this flow rate the purity of oxygen dropped to 50-60% according to the manual.
The next better model was twice as expensive, so I gave up on the idea.

Evgenly, could you find out the price in grivna for a concentrator in Ukraine that might suit our needs? Your currency exchange has gotten even worse since we met at our shop in Bucha in October. For those listening in, the Grivna to dollar used to be about 5 to 1 until the economic crash in 2008 in which it became 8 to 1. The unrest last year in Ukraine reduced it further to 13 to 1 in October and now it is around 30 to 1. While this is really bad for Ukrainians, I might be able to get a decent concentrator for our Ukraine shop without it being too expensive since the dollar is so strong right now. The great big oxygen bottle we now use is too big for one person to move and having an unlimited supply from a concentrator would be nice. Of course it depends on price. I’m guessing that we have a much bigger supply of used concentrators in the States so our prices would be lower here.

Also Evgenly you might be interested to know I am having a hobby version of my fixture made in Cherkassy because of the strength of the dollar. They did the original design work in 2008 and I had some samples made. Since then I’ve had them laser cut and etched out of stainless steel at a place near where I live in the States. However now that your economy is bad I can get them at a decent price in Ukraine. I’ll keep you posted. The daughter of the owner of the laser company in Ukraine was our translator at one time. She is married to an American and living over here now. She is going back home for a visit next month and will bring a sample back.

[holy-mojo]

Hi Sean / Devlin,

This is my first post so hope it works. I've recently bought a brand new Oxygen Concentrator from a company in Melbourne called NIche Gas Products (NICHE GAS PRODUCTS PTY LTD). They were super helpful and made up unique parts to suit the US equipment I'm using (Smith AW1A). I decided on the 10L/min version just in case. It's not cheap but still much lower cost than anything second hand on ebay or gumtree. It works absolutely fine for me running round the 2-3l/min mark - currently lining up and practicing on my 30 (recently revised to 50 in another thread! - WILL IT EVER END :-) ) fillet brazed joints before touching a real tube set.
The unit came fully boxed and well protected so I would imagine they can ship it for you.

Nic Topping
Melbourne, Australia

[waterlaz]

Evgenly, could you find out the price in grivna for a concentrator in Ukraine that might suit our needs? Your currency exchange has gotten even worse since we met at our shop in Bucha in October.

Sure. Just one silly question, what is the minimum oxygen flow?

[devlin]

hey Nic. thanks for the heads up. they carry some good gear as well. I'm getting a great 3 month rental price on a cylinder so will wait till I'm building a lot more frames before spending money on a concentrator. Good to know where to get one though that's purpose built.

Hi Sean / Devlin,

This is my first post so hope it works. I've recently bought a brand new Oxygen Concentrator from a company in Melbourne called NIche Gas Products (NICHE GAS PRODUCTS PTY LTD). They were super helpful and made up unique parts to suit the US equipment I'm using (Smith AW1A). I decided on the 10L/min version just in case. It's not cheap but still much lower cost than anything second hand on ebay or gumtree. It works absolutely fine for me running round the 2-3l/min mark - currently lining up and practicing on my 30 (recently revised to 50 in another thread! - WILL IT EVER END :-) ) fillet brazed joints before touching a real tube set.
The unit came fully boxed and well protected so I would imagine they can ship it for you.

Nic Topping
Melbourne, Australia

[Doug Fattic]

Just a data point on the output capacity of my DeVilbiss 5 liter per minute oxygen concentrator. Today I hooked up 2 torches to it and ran them at the same time. They both had a Victor size #4 tips working at normal working pressures (meaning the flame wasn’t turned down so low it was quiet or up so much it sounded like a jet engine). It is where I would set it under normal circumstances. Their orifice size is .073” or 1.85mm. It could run both of them at the same time without any trouble with the flowmeter turned up. The biggest tip I use when I build a frame is a #4. Most students never use anything bigger than a #3. So my concentrator produces twice the oxygen I ever need when building a frame.

Obviously there can be situations where more power is needed but having twice what I ever use is more than enough for me. YMMV. For example using a super big flame like Jon pointed out or a cutting torch like the other John mentioned. However if I was doing those things I’d probably want a bigger torch handle too. The one time I use a bigger flame is taking something apart on a frame. My oxygen concentrator still has enough capacity for a bigger flame than a #4 if I need it for that purpose. I mention this because there might be someone that hesitates getting a concentrator worrying that sometime it might not have enough capacity. That is theoretically possible but not probably when building a bicycle frame.

[Doug Fattic]

Sure. Just one silly question, what is the minimum oxygen flow?

5 liters per minute should work fine. Of course it wouldn't hurt to check the price of a bigger one.

[Mark Kelly]

Hi Sean / Devlin,

This is my first post so hope it works. I've recently bought a brand new Oxygen Concentrator from a company in Melbourne called NIche Gas Products (NICHE GAS PRODUCTS PTY LTD). They were super helpful and made up unique parts to suit the US equipment I'm using (Smith AW1A). I decided on the 10L/min version just in case. It's not cheap but still much lower cost than anything second hand on ebay or gumtree.
<snip>

Nic

Thanks for that, I might have to ask them about ones suitable for our yeast props. The only ones I've found so far are > $3k each.

[holy-mojo]

Hi Mark,

I've just checked the user manual and the outlet pressure is quoted as being between 40 & 80 kPa - a bit low for you if you're needing 500kPa I'm afraid. It certainly didn't have enough puff to flow more than 1-2l/min through the Type A torch mounted flashback arrestor no matter how much I turned up the flow valve, so I had to remove this from the line. Quoted O2 is 93+/-3.
Cheers
Nic (Topping)